Challenges Deploying Flink With Savepoints On Kubernetes

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Hao Sun
Yep I know that option. That's where get me confused as well. In a HA setup, where do I supply this option (allowNonRestoredState)?
This option requires a savepoint path when I start a flink job I remember. And HA does not require the path

Hao Sun


On Thu, Oct 10, 2019 at 11:16 AM Yun Tang <[hidden email]> wrote:
Just a minor supplement [hidden email], if you decided to drop a operator, don't forget to add --allowNonRestoredState (short: -n) option [1]



Best
Yun Tang


From: Vijay Bhaskar <[hidden email]>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <[hidden email]>
Cc: Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yun Tang <[hidden email]>; Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Thanks Yang. We will try and let you know if any issues arise

Regards
Bhaskar

On Thu, Oct 10, 2019 at 1:53 PM Yang Wang <[hidden email]> wrote:
@ Hao Sun,
I have made a confirmation that even we change parallelism and/or modify operators, add new operators,
the flink cluster could also recover from latest checkpoint.

@ Vijay
a) Some individual jobmanager/taskmanager crashed exceptionally(someother jobmanagers 
and taskmanagers are alive), it could recover from the latest checkpoint.
b) All jobmanagers and taskmanagers fails, it could still recover from the latest checkpoint if the cluster-id
is not changed. 

When we enable the HA, The meta of jobgraph and checkpoint is saved on zookeeper and the real files are save
on high-availability storage(HDFS). So when the flink application is submitted again with same cluster-id, it could
recover jobs and checkpoint from zookeeper. I think it has been supported for a long time. Maybe you could have a
try with flink-1.8 or 1.9.

Best,
Yang


Vijay Bhaskar <[hidden email]> 于2019年10月10日周四 下午2:26写道:
Thanks Yang and Sean. I have couple of questions:

1) Suppose the scenario of , bringing back entire cluster,
     a) In that case, at least one job manager out of HA group should be up and running right? or
     b) All the job managers fails, then also this works? In that case please let me know the procedure/share the documentation? 
         How to start from previous check point?
         What Flink version onwards this feature is stable?

Regards
Bhaskar


On Wed, Oct 9, 2019 at 8:51 AM Yang Wang <[hidden email]> wrote:
Hi Vijay,

If you are using HA solution, i think you do not need to specify the savepoint. Instead the checkpoint is used.
The checkpoint is done automatically and periodically based on your configuration.When the 
jobmanager/taskmanager fails or the whole cluster crashes, it could always recover from the latest
checkpoint. Does this meed your requirement?

Best,
Yang

Sean Hester <[hidden email]> 于2019年10月1日周二 上午1:47写道:
Vijay,

That is my understanding as well: the HA solution only solves the problem up to the point all job managers fail/restart at the same time. That's where my original concern was. 

But to Aleksandar and Yun's point, running in HA with 2 or 3 Job Managers per cluster--as long as they are all deployed to separate GKE nodes--would provide a very high uptime/low failure rate, at least on paper. It's a promising enough option that we're going to run in HA for a month or two and monitor results before we put in any extra work to customize the savepoint start-up behavior.

On Fri, Sep 27, 2019 at 2:24 AM Vijay Bhaskar <[hidden email]> wrote:
I don't think HA will help to recover from cluster crash, for that we should take periodic savepoint right? Please correct me in case i am wrong

Regards
Bhaskar

On Fri, Sep 27, 2019 at 11:48 AM Vijay Bhaskar <[hidden email]> wrote:
Suppose my cluster got crashed and need to bring up the entire cluster back? Does HA still helps to run the cluster from latest save point? 

Regards
Bhaskar

On Thu, Sep 26, 2019 at 7:44 PM Sean Hester <[hidden email]> wrote:
thanks to everyone for all the replies.

i think the original concern here with "just" relying on the HA option is that there are some disaster recovery and data center migration use cases where the continuity of the job managers is difficult to preserve. but those are admittedly very edgy use cases. i think it's definitely worth reviewing the SLAs with our site reliability engineers to see how likely it would be to completely lose all job managers under an HA configuration. that small a risk might be acceptable/preferable to a one-off solution.

@Aleksander, would love to learn more about Zookeeper-less HA. i think i spotted a thread somewhere between Till and someone (perhaps you) about that. feel free to DM me.

thanks again to everyone!

On Thu, Sep 26, 2019 at 7:32 AM Yang Wang <[hidden email]> wrote:
Hi, Aleksandar

Savepoint option in standalone job cluster is optional. If you want to always recover 
from the latest checkpoint, just as Aleksandar and Yun Tang said you could use the 
high-availability configuration. Make sure the cluster-id is not changed, i think the job 
could recover both at exceptionally crash and restart by expectation.

[hidden email], we are also have an zookeeper-less high-availability implementation[1].
Maybe we could have some discussion and contribute this useful feature to the community.


Best,
Yang

Aleksandar Mastilovic <[hidden email]> 于2019年9月26日周四 上午4:11写道:
Would you guys (Flink devs) be interested in our solution for zookeeper-less HA? I could ask the managers how they feel about open-sourcing the improvement.

On Sep 25, 2019, at 11:49 AM, Yun Tang <[hidden email]> wrote:

As Aleksandar said, k8s with HA configuration could solve your problem. There already have some discussion about how to implement such HA in k8s if we don't have a zookeeper service: FLINK-11105 [1] and FLINK-12884 [2]. Currently, you might only have to choose zookeeper as high-availability service.


Best
Yun Tang

From: Aleksandar Mastilovic <[hidden email]>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <[hidden email]>
Cc: Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Can’t you simply use JobManager in HA mode? It would pick up where it left off if you don’t provide a Savepoint.

On Sep 25, 2019, at 6:07 AM, Sean Hester <[hidden email]> wrote:

thanks for all replies! i'll definitely take a look at the Flink k8s Operator project.

i'll try to restate the issue to clarify. this issue is specific to starting a job from a savepoint in job-cluster mode. in these cases the Job Manager container is configured to run a single Flink job at start-up. the savepoint needs to be provided as an argument to the entrypoint. the Flink documentation for this approach is here:


the issue is that taking this approach means that the job will always start from the savepoint provided as the start argument in the Kubernetes YAML. this includes unplanned restarts of the job manager, but we'd really prefer any unplanned restarts resume for the most recent checkpoint instead of restarting from the configured savepoint. so in a sense we want the savepoint argument to be transient, only being used during the initial deployment, but this runs counter to the design of Kubernetes which always wants to restore a deployment to the "goal state" as defined in the YAML.

i hope this helps. if you want more details please let me know, and thanks again for your time.


On Tue, Sep 24, 2019 at 1:09 PM Hao Sun <[hidden email]> wrote:
I think I overlooked it. Good point. I am using Redis to save the path to my savepoint, I might be able to set a TTL to avoid such issue.

Hao Sun


On Tue, Sep 24, 2019 at 9:54 AM Yuval Itzchakov <[hidden email]> wrote:
Hi Hao,

I think he's exactly talking about the usecase where the JM/TM restart and they come back up from the latest savepoint which might be stale by that time.

On Tue, 24 Sep 2019, 19:24 Hao Sun, <[hidden email]> wrote:
We always make a savepoint before we shutdown the job-cluster. So the savepoint is always the latest. When we fix a bug or change the job graph, it can resume well.
We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM, uncaught exception, etc.

Maybe I do not understand your use case well, I do not see a need to start from checkpoint after a bug fix.
From what I know, currently you can use checkpoint as a savepoint as well

Hao Sun


On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
AFAIK there's currently nothing implemented to solve this problem, but working on a possible fix can be implemented on top of https://github.com/lyft/flinkk8soperator which already has a pretty fancy state machine for rolling upgrades. I'd love to be involved as this is an issue I've been thinking about as well.

Yuval

On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]> wrote:
hi all--we've run into a gap (knowledge? design? tbd?) for our use cases when deploying Flink jobs to start from savepoints using the job-cluster mode in Kubernetes.

we're running a ~15 different jobs, all in job-cluster mode, using a mix of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are all long-running streaming jobs, all essentially acting as microservices. we're using Helm charts to configure all of our deployments.

we have a number of use cases where we want to restart jobs from a savepoint to replay recent events, i.e. when we've enhanced the job logic or fixed a bug. but after the deployment we want to have the job resume it's "long-running" behavior, where any unplanned restarts resume from the latest checkpoint.

the issue we run into is that any obvious/standard/idiomatic Kubernetes deployment includes the savepoint argument in the configuration. if the Job Manager container(s) have an unplanned restart, when they come back up they will start from the savepoint instead of resuming from the latest checkpoint. everything is working as configured, but that's not exactly what we want. we want the savepoint argument to be transient somehow (only used during the initial deployment), but Kubernetes doesn't really support the concept of transient configuration.

i can see a couple of potential solutions that either involve custom code in the jobs or custom logic in the container (i.e. a custom entrypoint script that records that the configured savepoint has already been used in a file on a persistent volume or GCS, and potentially when/why/by which deployment). but these seem like unexpected and hacky solutions. before we head down that road i wanted to ask:
  • is this is already a solved problem that i've missed?
  • is this issue already on the community's radar?
thanks in advance!

-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



-- 
Best Regards,
Yuval Itzchakov.


-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Yun Tang
Hi Hao

It seems that I misunderstood the background of usage for your cases. High availability configuration targets for fault tolerance not for general development evolution. If you want to change your job topology, just follow the general rule to restore from savepoint/checkpoint, do not rely on HA to do job migration things. 

Best
Yun Tang

From: Hao Sun <[hidden email]>
Sent: Friday, October 11, 2019 8:33
To: Yun Tang <[hidden email]>
Cc: Vijay Bhaskar <[hidden email]>; Yang Wang <[hidden email]>; Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Yep I know that option. That's where get me confused as well. In a HA setup, where do I supply this option (allowNonRestoredState)?
This option requires a savepoint path when I start a flink job I remember. And HA does not require the path

Hao Sun


On Thu, Oct 10, 2019 at 11:16 AM Yun Tang <[hidden email]> wrote:
Just a minor supplement [hidden email], if you decided to drop a operator, don't forget to add --allowNonRestoredState (short: -n) option [1]



Best
Yun Tang


From: Vijay Bhaskar <[hidden email]>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <[hidden email]>
Cc: Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yun Tang <[hidden email]>; Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Thanks Yang. We will try and let you know if any issues arise

Regards
Bhaskar

On Thu, Oct 10, 2019 at 1:53 PM Yang Wang <[hidden email]> wrote:
@ Hao Sun,
I have made a confirmation that even we change parallelism and/or modify operators, add new operators,
the flink cluster could also recover from latest checkpoint.

@ Vijay
a) Some individual jobmanager/taskmanager crashed exceptionally(someother jobmanagers 
and taskmanagers are alive), it could recover from the latest checkpoint.
b) All jobmanagers and taskmanagers fails, it could still recover from the latest checkpoint if the cluster-id
is not changed. 

When we enable the HA, The meta of jobgraph and checkpoint is saved on zookeeper and the real files are save
on high-availability storage(HDFS). So when the flink application is submitted again with same cluster-id, it could
recover jobs and checkpoint from zookeeper. I think it has been supported for a long time. Maybe you could have a
try with flink-1.8 or 1.9.

Best,
Yang


Vijay Bhaskar <[hidden email]> 于2019年10月10日周四 下午2:26写道:
Thanks Yang and Sean. I have couple of questions:

1) Suppose the scenario of , bringing back entire cluster,
     a) In that case, at least one job manager out of HA group should be up and running right? or
     b) All the job managers fails, then also this works? In that case please let me know the procedure/share the documentation? 
         How to start from previous check point?
         What Flink version onwards this feature is stable?

Regards
Bhaskar


On Wed, Oct 9, 2019 at 8:51 AM Yang Wang <[hidden email]> wrote:
Hi Vijay,

If you are using HA solution, i think you do not need to specify the savepoint. Instead the checkpoint is used.
The checkpoint is done automatically and periodically based on your configuration.When the 
jobmanager/taskmanager fails or the whole cluster crashes, it could always recover from the latest
checkpoint. Does this meed your requirement?

Best,
Yang

Sean Hester <[hidden email]> 于2019年10月1日周二 上午1:47写道:
Vijay,

That is my understanding as well: the HA solution only solves the problem up to the point all job managers fail/restart at the same time. That's where my original concern was. 

But to Aleksandar and Yun's point, running in HA with 2 or 3 Job Managers per cluster--as long as they are all deployed to separate GKE nodes--would provide a very high uptime/low failure rate, at least on paper. It's a promising enough option that we're going to run in HA for a month or two and monitor results before we put in any extra work to customize the savepoint start-up behavior.

On Fri, Sep 27, 2019 at 2:24 AM Vijay Bhaskar <[hidden email]> wrote:
I don't think HA will help to recover from cluster crash, for that we should take periodic savepoint right? Please correct me in case i am wrong

Regards
Bhaskar

On Fri, Sep 27, 2019 at 11:48 AM Vijay Bhaskar <[hidden email]> wrote:
Suppose my cluster got crashed and need to bring up the entire cluster back? Does HA still helps to run the cluster from latest save point? 

Regards
Bhaskar

On Thu, Sep 26, 2019 at 7:44 PM Sean Hester <[hidden email]> wrote:
thanks to everyone for all the replies.

i think the original concern here with "just" relying on the HA option is that there are some disaster recovery and data center migration use cases where the continuity of the job managers is difficult to preserve. but those are admittedly very edgy use cases. i think it's definitely worth reviewing the SLAs with our site reliability engineers to see how likely it would be to completely lose all job managers under an HA configuration. that small a risk might be acceptable/preferable to a one-off solution.

@Aleksander, would love to learn more about Zookeeper-less HA. i think i spotted a thread somewhere between Till and someone (perhaps you) about that. feel free to DM me.

thanks again to everyone!

On Thu, Sep 26, 2019 at 7:32 AM Yang Wang <[hidden email]> wrote:
Hi, Aleksandar

Savepoint option in standalone job cluster is optional. If you want to always recover 
from the latest checkpoint, just as Aleksandar and Yun Tang said you could use the 
high-availability configuration. Make sure the cluster-id is not changed, i think the job 
could recover both at exceptionally crash and restart by expectation.

[hidden email], we are also have an zookeeper-less high-availability implementation[1].
Maybe we could have some discussion and contribute this useful feature to the community.


Best,
Yang

Aleksandar Mastilovic <[hidden email]> 于2019年9月26日周四 上午4:11写道:
Would you guys (Flink devs) be interested in our solution for zookeeper-less HA? I could ask the managers how they feel about open-sourcing the improvement.

On Sep 25, 2019, at 11:49 AM, Yun Tang <[hidden email]> wrote:

As Aleksandar said, k8s with HA configuration could solve your problem. There already have some discussion about how to implement such HA in k8s if we don't have a zookeeper service: FLINK-11105 [1] and FLINK-12884 [2]. Currently, you might only have to choose zookeeper as high-availability service.


Best
Yun Tang

From: Aleksandar Mastilovic <[hidden email]>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <[hidden email]>
Cc: Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Can’t you simply use JobManager in HA mode? It would pick up where it left off if you don’t provide a Savepoint.

On Sep 25, 2019, at 6:07 AM, Sean Hester <[hidden email]> wrote:

thanks for all replies! i'll definitely take a look at the Flink k8s Operator project.

i'll try to restate the issue to clarify. this issue is specific to starting a job from a savepoint in job-cluster mode. in these cases the Job Manager container is configured to run a single Flink job at start-up. the savepoint needs to be provided as an argument to the entrypoint. the Flink documentation for this approach is here:


the issue is that taking this approach means that the job will always start from the savepoint provided as the start argument in the Kubernetes YAML. this includes unplanned restarts of the job manager, but we'd really prefer any unplanned restarts resume for the most recent checkpoint instead of restarting from the configured savepoint. so in a sense we want the savepoint argument to be transient, only being used during the initial deployment, but this runs counter to the design of Kubernetes which always wants to restore a deployment to the "goal state" as defined in the YAML.

i hope this helps. if you want more details please let me know, and thanks again for your time.


On Tue, Sep 24, 2019 at 1:09 PM Hao Sun <[hidden email]> wrote:
I think I overlooked it. Good point. I am using Redis to save the path to my savepoint, I might be able to set a TTL to avoid such issue.

Hao Sun


On Tue, Sep 24, 2019 at 9:54 AM Yuval Itzchakov <[hidden email]> wrote:
Hi Hao,

I think he's exactly talking about the usecase where the JM/TM restart and they come back up from the latest savepoint which might be stale by that time.

On Tue, 24 Sep 2019, 19:24 Hao Sun, <[hidden email]> wrote:
We always make a savepoint before we shutdown the job-cluster. So the savepoint is always the latest. When we fix a bug or change the job graph, it can resume well.
We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM, uncaught exception, etc.

Maybe I do not understand your use case well, I do not see a need to start from checkpoint after a bug fix.
From what I know, currently you can use checkpoint as a savepoint as well

Hao Sun


On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
AFAIK there's currently nothing implemented to solve this problem, but working on a possible fix can be implemented on top of https://github.com/lyft/flinkk8soperator which already has a pretty fancy state machine for rolling upgrades. I'd love to be involved as this is an issue I've been thinking about as well.

Yuval

On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]> wrote:
hi all--we've run into a gap (knowledge? design? tbd?) for our use cases when deploying Flink jobs to start from savepoints using the job-cluster mode in Kubernetes.

we're running a ~15 different jobs, all in job-cluster mode, using a mix of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are all long-running streaming jobs, all essentially acting as microservices. we're using Helm charts to configure all of our deployments.

we have a number of use cases where we want to restart jobs from a savepoint to replay recent events, i.e. when we've enhanced the job logic or fixed a bug. but after the deployment we want to have the job resume it's "long-running" behavior, where any unplanned restarts resume from the latest checkpoint.

the issue we run into is that any obvious/standard/idiomatic Kubernetes deployment includes the savepoint argument in the configuration. if the Job Manager container(s) have an unplanned restart, when they come back up they will start from the savepoint instead of resuming from the latest checkpoint. everything is working as configured, but that's not exactly what we want. we want the savepoint argument to be transient somehow (only used during the initial deployment), but Kubernetes doesn't really support the concept of transient configuration.

i can see a couple of potential solutions that either involve custom code in the jobs or custom logic in the container (i.e. a custom entrypoint script that records that the configured savepoint has already been used in a file on a persistent volume or GCS, and potentially when/why/by which deployment). but these seem like unexpected and hacky solutions. before we head down that road i wanted to ask:
  • is this is already a solved problem that i've missed?
  • is this issue already on the community's radar?
thanks in advance!

-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



-- 
Best Regards,
Yuval Itzchakov.


-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Vijay Bhaskar
We are seeing below logs in production sometime ago, after that we stopped HA. Do you people think HA is enabled properly from the below logs?

Regards
Bhaskar

2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderelection.ZooKeeperLeaderElectionService  - Starting ZooKeeperLeaderElectionService ZooKeeperLeaderElectionService{leaderPath='/leader/dispatcher_lock'}.
2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderretrieval.ZooKeeperLeaderRetrievalService  - Starting ZooKeeperLeaderRetrievalService /leader/dispatcher_lock.
2019-09-24 17:40:20,975 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:20,976 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:23,976 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:23,977 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:26,982 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:26,983 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:29,988 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:29,988 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:32,994 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:32,995 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:36,000 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:36,001 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:39,006 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host

On Fri, Oct 11, 2019 at 9:39 AM Yun Tang <[hidden email]> wrote:
Hi Hao

It seems that I misunderstood the background of usage for your cases. High availability configuration targets for fault tolerance not for general development evolution. If you want to change your job topology, just follow the general rule to restore from savepoint/checkpoint, do not rely on HA to do job migration things. 

Best
Yun Tang

From: Hao Sun <[hidden email]>
Sent: Friday, October 11, 2019 8:33
To: Yun Tang <[hidden email]>
Cc: Vijay Bhaskar <[hidden email]>; Yang Wang <[hidden email]>; Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Yep I know that option. That's where get me confused as well. In a HA setup, where do I supply this option (allowNonRestoredState)?
This option requires a savepoint path when I start a flink job I remember. And HA does not require the path

Hao Sun


On Thu, Oct 10, 2019 at 11:16 AM Yun Tang <[hidden email]> wrote:
Just a minor supplement [hidden email], if you decided to drop a operator, don't forget to add --allowNonRestoredState (short: -n) option [1]



Best
Yun Tang


From: Vijay Bhaskar <[hidden email]>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <[hidden email]>
Cc: Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yun Tang <[hidden email]>; Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Thanks Yang. We will try and let you know if any issues arise

Regards
Bhaskar

On Thu, Oct 10, 2019 at 1:53 PM Yang Wang <[hidden email]> wrote:
@ Hao Sun,
I have made a confirmation that even we change parallelism and/or modify operators, add new operators,
the flink cluster could also recover from latest checkpoint.

@ Vijay
a) Some individual jobmanager/taskmanager crashed exceptionally(someother jobmanagers 
and taskmanagers are alive), it could recover from the latest checkpoint.
b) All jobmanagers and taskmanagers fails, it could still recover from the latest checkpoint if the cluster-id
is not changed. 

When we enable the HA, The meta of jobgraph and checkpoint is saved on zookeeper and the real files are save
on high-availability storage(HDFS). So when the flink application is submitted again with same cluster-id, it could
recover jobs and checkpoint from zookeeper. I think it has been supported for a long time. Maybe you could have a
try with flink-1.8 or 1.9.

Best,
Yang


Vijay Bhaskar <[hidden email]> 于2019年10月10日周四 下午2:26写道:
Thanks Yang and Sean. I have couple of questions:

1) Suppose the scenario of , bringing back entire cluster,
     a) In that case, at least one job manager out of HA group should be up and running right? or
     b) All the job managers fails, then also this works? In that case please let me know the procedure/share the documentation? 
         How to start from previous check point?
         What Flink version onwards this feature is stable?

Regards
Bhaskar


On Wed, Oct 9, 2019 at 8:51 AM Yang Wang <[hidden email]> wrote:
Hi Vijay,

If you are using HA solution, i think you do not need to specify the savepoint. Instead the checkpoint is used.
The checkpoint is done automatically and periodically based on your configuration.When the 
jobmanager/taskmanager fails or the whole cluster crashes, it could always recover from the latest
checkpoint. Does this meed your requirement?

Best,
Yang

Sean Hester <[hidden email]> 于2019年10月1日周二 上午1:47写道:
Vijay,

That is my understanding as well: the HA solution only solves the problem up to the point all job managers fail/restart at the same time. That's where my original concern was. 

But to Aleksandar and Yun's point, running in HA with 2 or 3 Job Managers per cluster--as long as they are all deployed to separate GKE nodes--would provide a very high uptime/low failure rate, at least on paper. It's a promising enough option that we're going to run in HA for a month or two and monitor results before we put in any extra work to customize the savepoint start-up behavior.

On Fri, Sep 27, 2019 at 2:24 AM Vijay Bhaskar <[hidden email]> wrote:
I don't think HA will help to recover from cluster crash, for that we should take periodic savepoint right? Please correct me in case i am wrong

Regards
Bhaskar

On Fri, Sep 27, 2019 at 11:48 AM Vijay Bhaskar <[hidden email]> wrote:
Suppose my cluster got crashed and need to bring up the entire cluster back? Does HA still helps to run the cluster from latest save point? 

Regards
Bhaskar

On Thu, Sep 26, 2019 at 7:44 PM Sean Hester <[hidden email]> wrote:
thanks to everyone for all the replies.

i think the original concern here with "just" relying on the HA option is that there are some disaster recovery and data center migration use cases where the continuity of the job managers is difficult to preserve. but those are admittedly very edgy use cases. i think it's definitely worth reviewing the SLAs with our site reliability engineers to see how likely it would be to completely lose all job managers under an HA configuration. that small a risk might be acceptable/preferable to a one-off solution.

@Aleksander, would love to learn more about Zookeeper-less HA. i think i spotted a thread somewhere between Till and someone (perhaps you) about that. feel free to DM me.

thanks again to everyone!

On Thu, Sep 26, 2019 at 7:32 AM Yang Wang <[hidden email]> wrote:
Hi, Aleksandar

Savepoint option in standalone job cluster is optional. If you want to always recover 
from the latest checkpoint, just as Aleksandar and Yun Tang said you could use the 
high-availability configuration. Make sure the cluster-id is not changed, i think the job 
could recover both at exceptionally crash and restart by expectation.

[hidden email], we are also have an zookeeper-less high-availability implementation[1].
Maybe we could have some discussion and contribute this useful feature to the community.


Best,
Yang

Aleksandar Mastilovic <[hidden email]> 于2019年9月26日周四 上午4:11写道:
Would you guys (Flink devs) be interested in our solution for zookeeper-less HA? I could ask the managers how they feel about open-sourcing the improvement.

On Sep 25, 2019, at 11:49 AM, Yun Tang <[hidden email]> wrote:

As Aleksandar said, k8s with HA configuration could solve your problem. There already have some discussion about how to implement such HA in k8s if we don't have a zookeeper service: FLINK-11105 [1] and FLINK-12884 [2]. Currently, you might only have to choose zookeeper as high-availability service.


Best
Yun Tang

From: Aleksandar Mastilovic <[hidden email]>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <[hidden email]>
Cc: Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Can’t you simply use JobManager in HA mode? It would pick up where it left off if you don’t provide a Savepoint.

On Sep 25, 2019, at 6:07 AM, Sean Hester <[hidden email]> wrote:

thanks for all replies! i'll definitely take a look at the Flink k8s Operator project.

i'll try to restate the issue to clarify. this issue is specific to starting a job from a savepoint in job-cluster mode. in these cases the Job Manager container is configured to run a single Flink job at start-up. the savepoint needs to be provided as an argument to the entrypoint. the Flink documentation for this approach is here:


the issue is that taking this approach means that the job will always start from the savepoint provided as the start argument in the Kubernetes YAML. this includes unplanned restarts of the job manager, but we'd really prefer any unplanned restarts resume for the most recent checkpoint instead of restarting from the configured savepoint. so in a sense we want the savepoint argument to be transient, only being used during the initial deployment, but this runs counter to the design of Kubernetes which always wants to restore a deployment to the "goal state" as defined in the YAML.

i hope this helps. if you want more details please let me know, and thanks again for your time.


On Tue, Sep 24, 2019 at 1:09 PM Hao Sun <[hidden email]> wrote:
I think I overlooked it. Good point. I am using Redis to save the path to my savepoint, I might be able to set a TTL to avoid such issue.

Hao Sun


On Tue, Sep 24, 2019 at 9:54 AM Yuval Itzchakov <[hidden email]> wrote:
Hi Hao,

I think he's exactly talking about the usecase where the JM/TM restart and they come back up from the latest savepoint which might be stale by that time.

On Tue, 24 Sep 2019, 19:24 Hao Sun, <[hidden email]> wrote:
We always make a savepoint before we shutdown the job-cluster. So the savepoint is always the latest. When we fix a bug or change the job graph, it can resume well.
We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM, uncaught exception, etc.

Maybe I do not understand your use case well, I do not see a need to start from checkpoint after a bug fix.
From what I know, currently you can use checkpoint as a savepoint as well

Hao Sun


On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
AFAIK there's currently nothing implemented to solve this problem, but working on a possible fix can be implemented on top of https://github.com/lyft/flinkk8soperator which already has a pretty fancy state machine for rolling upgrades. I'd love to be involved as this is an issue I've been thinking about as well.

Yuval

On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]> wrote:
hi all--we've run into a gap (knowledge? design? tbd?) for our use cases when deploying Flink jobs to start from savepoints using the job-cluster mode in Kubernetes.

we're running a ~15 different jobs, all in job-cluster mode, using a mix of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are all long-running streaming jobs, all essentially acting as microservices. we're using Helm charts to configure all of our deployments.

we have a number of use cases where we want to restart jobs from a savepoint to replay recent events, i.e. when we've enhanced the job logic or fixed a bug. but after the deployment we want to have the job resume it's "long-running" behavior, where any unplanned restarts resume from the latest checkpoint.

the issue we run into is that any obvious/standard/idiomatic Kubernetes deployment includes the savepoint argument in the configuration. if the Job Manager container(s) have an unplanned restart, when they come back up they will start from the savepoint instead of resuming from the latest checkpoint. everything is working as configured, but that's not exactly what we want. we want the savepoint argument to be transient somehow (only used during the initial deployment), but Kubernetes doesn't really support the concept of transient configuration.

i can see a couple of potential solutions that either involve custom code in the jobs or custom logic in the container (i.e. a custom entrypoint script that records that the configured savepoint has already been used in a file on a persistent volume or GCS, and potentially when/why/by which deployment). but these seem like unexpected and hacky solutions. before we head down that road i wanted to ask:
  • is this is already a solved problem that i've missed?
  • is this issue already on the community's radar?
thanks in advance!

-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



-- 
Best Regards,
Yuval Itzchakov.


-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Vijay Bhaskar
Apart from these we have other environment and there check point worked fine in HA mode with complete cluster restart. But one of the job we are seeing an issue, in zookeeper the check point path is retrieved and its unable to find the check point path in persistent storage. I am wondering why this would happen first of all?  
Is there any sync issue between file writing over persistent path and file registration with HA service? For example check point has been registered in zookeeper but has not been written yet while restarting the cluster?  I suspect this kind of problem can happen. We are using flink 1.6.2 in production. Is this an issue already known before and fixed recently

Regards
Bhaskar

On Fri, Oct 11, 2019 at 2:08 PM Vijay Bhaskar <[hidden email]> wrote:
We are seeing below logs in production sometime ago, after that we stopped HA. Do you people think HA is enabled properly from the below logs?

Regards
Bhaskar

2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderelection.ZooKeeperLeaderElectionService  - Starting ZooKeeperLeaderElectionService ZooKeeperLeaderElectionService{leaderPath='/leader/dispatcher_lock'}.
2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderretrieval.ZooKeeperLeaderRetrievalService  - Starting ZooKeeperLeaderRetrievalService /leader/dispatcher_lock.
2019-09-24 17:40:20,975 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:20,976 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:23,976 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:23,977 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:26,982 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:26,983 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:29,988 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:29,988 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:32,994 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:32,995 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:36,000 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:36,001 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:39,006 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host

On Fri, Oct 11, 2019 at 9:39 AM Yun Tang <[hidden email]> wrote:
Hi Hao

It seems that I misunderstood the background of usage for your cases. High availability configuration targets for fault tolerance not for general development evolution. If you want to change your job topology, just follow the general rule to restore from savepoint/checkpoint, do not rely on HA to do job migration things. 

Best
Yun Tang

From: Hao Sun <[hidden email]>
Sent: Friday, October 11, 2019 8:33
To: Yun Tang <[hidden email]>
Cc: Vijay Bhaskar <[hidden email]>; Yang Wang <[hidden email]>; Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Yep I know that option. That's where get me confused as well. In a HA setup, where do I supply this option (allowNonRestoredState)?
This option requires a savepoint path when I start a flink job I remember. And HA does not require the path

Hao Sun


On Thu, Oct 10, 2019 at 11:16 AM Yun Tang <[hidden email]> wrote:
Just a minor supplement [hidden email], if you decided to drop a operator, don't forget to add --allowNonRestoredState (short: -n) option [1]



Best
Yun Tang


From: Vijay Bhaskar <[hidden email]>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <[hidden email]>
Cc: Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yun Tang <[hidden email]>; Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Thanks Yang. We will try and let you know if any issues arise

Regards
Bhaskar

On Thu, Oct 10, 2019 at 1:53 PM Yang Wang <[hidden email]> wrote:
@ Hao Sun,
I have made a confirmation that even we change parallelism and/or modify operators, add new operators,
the flink cluster could also recover from latest checkpoint.

@ Vijay
a) Some individual jobmanager/taskmanager crashed exceptionally(someother jobmanagers 
and taskmanagers are alive), it could recover from the latest checkpoint.
b) All jobmanagers and taskmanagers fails, it could still recover from the latest checkpoint if the cluster-id
is not changed. 

When we enable the HA, The meta of jobgraph and checkpoint is saved on zookeeper and the real files are save
on high-availability storage(HDFS). So when the flink application is submitted again with same cluster-id, it could
recover jobs and checkpoint from zookeeper. I think it has been supported for a long time. Maybe you could have a
try with flink-1.8 or 1.9.

Best,
Yang


Vijay Bhaskar <[hidden email]> 于2019年10月10日周四 下午2:26写道:
Thanks Yang and Sean. I have couple of questions:

1) Suppose the scenario of , bringing back entire cluster,
     a) In that case, at least one job manager out of HA group should be up and running right? or
     b) All the job managers fails, then also this works? In that case please let me know the procedure/share the documentation? 
         How to start from previous check point?
         What Flink version onwards this feature is stable?

Regards
Bhaskar


On Wed, Oct 9, 2019 at 8:51 AM Yang Wang <[hidden email]> wrote:
Hi Vijay,

If you are using HA solution, i think you do not need to specify the savepoint. Instead the checkpoint is used.
The checkpoint is done automatically and periodically based on your configuration.When the 
jobmanager/taskmanager fails or the whole cluster crashes, it could always recover from the latest
checkpoint. Does this meed your requirement?

Best,
Yang

Sean Hester <[hidden email]> 于2019年10月1日周二 上午1:47写道:
Vijay,

That is my understanding as well: the HA solution only solves the problem up to the point all job managers fail/restart at the same time. That's where my original concern was. 

But to Aleksandar and Yun's point, running in HA with 2 or 3 Job Managers per cluster--as long as they are all deployed to separate GKE nodes--would provide a very high uptime/low failure rate, at least on paper. It's a promising enough option that we're going to run in HA for a month or two and monitor results before we put in any extra work to customize the savepoint start-up behavior.

On Fri, Sep 27, 2019 at 2:24 AM Vijay Bhaskar <[hidden email]> wrote:
I don't think HA will help to recover from cluster crash, for that we should take periodic savepoint right? Please correct me in case i am wrong

Regards
Bhaskar

On Fri, Sep 27, 2019 at 11:48 AM Vijay Bhaskar <[hidden email]> wrote:
Suppose my cluster got crashed and need to bring up the entire cluster back? Does HA still helps to run the cluster from latest save point? 

Regards
Bhaskar

On Thu, Sep 26, 2019 at 7:44 PM Sean Hester <[hidden email]> wrote:
thanks to everyone for all the replies.

i think the original concern here with "just" relying on the HA option is that there are some disaster recovery and data center migration use cases where the continuity of the job managers is difficult to preserve. but those are admittedly very edgy use cases. i think it's definitely worth reviewing the SLAs with our site reliability engineers to see how likely it would be to completely lose all job managers under an HA configuration. that small a risk might be acceptable/preferable to a one-off solution.

@Aleksander, would love to learn more about Zookeeper-less HA. i think i spotted a thread somewhere between Till and someone (perhaps you) about that. feel free to DM me.

thanks again to everyone!

On Thu, Sep 26, 2019 at 7:32 AM Yang Wang <[hidden email]> wrote:
Hi, Aleksandar

Savepoint option in standalone job cluster is optional. If you want to always recover 
from the latest checkpoint, just as Aleksandar and Yun Tang said you could use the 
high-availability configuration. Make sure the cluster-id is not changed, i think the job 
could recover both at exceptionally crash and restart by expectation.

[hidden email], we are also have an zookeeper-less high-availability implementation[1].
Maybe we could have some discussion and contribute this useful feature to the community.


Best,
Yang

Aleksandar Mastilovic <[hidden email]> 于2019年9月26日周四 上午4:11写道:
Would you guys (Flink devs) be interested in our solution for zookeeper-less HA? I could ask the managers how they feel about open-sourcing the improvement.

On Sep 25, 2019, at 11:49 AM, Yun Tang <[hidden email]> wrote:

As Aleksandar said, k8s with HA configuration could solve your problem. There already have some discussion about how to implement such HA in k8s if we don't have a zookeeper service: FLINK-11105 [1] and FLINK-12884 [2]. Currently, you might only have to choose zookeeper as high-availability service.


Best
Yun Tang

From: Aleksandar Mastilovic <[hidden email]>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <[hidden email]>
Cc: Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Can’t you simply use JobManager in HA mode? It would pick up where it left off if you don’t provide a Savepoint.

On Sep 25, 2019, at 6:07 AM, Sean Hester <[hidden email]> wrote:

thanks for all replies! i'll definitely take a look at the Flink k8s Operator project.

i'll try to restate the issue to clarify. this issue is specific to starting a job from a savepoint in job-cluster mode. in these cases the Job Manager container is configured to run a single Flink job at start-up. the savepoint needs to be provided as an argument to the entrypoint. the Flink documentation for this approach is here:


the issue is that taking this approach means that the job will always start from the savepoint provided as the start argument in the Kubernetes YAML. this includes unplanned restarts of the job manager, but we'd really prefer any unplanned restarts resume for the most recent checkpoint instead of restarting from the configured savepoint. so in a sense we want the savepoint argument to be transient, only being used during the initial deployment, but this runs counter to the design of Kubernetes which always wants to restore a deployment to the "goal state" as defined in the YAML.

i hope this helps. if you want more details please let me know, and thanks again for your time.


On Tue, Sep 24, 2019 at 1:09 PM Hao Sun <[hidden email]> wrote:
I think I overlooked it. Good point. I am using Redis to save the path to my savepoint, I might be able to set a TTL to avoid such issue.

Hao Sun


On Tue, Sep 24, 2019 at 9:54 AM Yuval Itzchakov <[hidden email]> wrote:
Hi Hao,

I think he's exactly talking about the usecase where the JM/TM restart and they come back up from the latest savepoint which might be stale by that time.

On Tue, 24 Sep 2019, 19:24 Hao Sun, <[hidden email]> wrote:
We always make a savepoint before we shutdown the job-cluster. So the savepoint is always the latest. When we fix a bug or change the job graph, it can resume well.
We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM, uncaught exception, etc.

Maybe I do not understand your use case well, I do not see a need to start from checkpoint after a bug fix.
From what I know, currently you can use checkpoint as a savepoint as well

Hao Sun


On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
AFAIK there's currently nothing implemented to solve this problem, but working on a possible fix can be implemented on top of https://github.com/lyft/flinkk8soperator which already has a pretty fancy state machine for rolling upgrades. I'd love to be involved as this is an issue I've been thinking about as well.

Yuval

On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]> wrote:
hi all--we've run into a gap (knowledge? design? tbd?) for our use cases when deploying Flink jobs to start from savepoints using the job-cluster mode in Kubernetes.

we're running a ~15 different jobs, all in job-cluster mode, using a mix of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are all long-running streaming jobs, all essentially acting as microservices. we're using Helm charts to configure all of our deployments.

we have a number of use cases where we want to restart jobs from a savepoint to replay recent events, i.e. when we've enhanced the job logic or fixed a bug. but after the deployment we want to have the job resume it's "long-running" behavior, where any unplanned restarts resume from the latest checkpoint.

the issue we run into is that any obvious/standard/idiomatic Kubernetes deployment includes the savepoint argument in the configuration. if the Job Manager container(s) have an unplanned restart, when they come back up they will start from the savepoint instead of resuming from the latest checkpoint. everything is working as configured, but that's not exactly what we want. we want the savepoint argument to be transient somehow (only used during the initial deployment), but Kubernetes doesn't really support the concept of transient configuration.

i can see a couple of potential solutions that either involve custom code in the jobs or custom logic in the container (i.e. a custom entrypoint script that records that the configured savepoint has already been used in a file on a persistent volume or GCS, and potentially when/why/by which deployment). but these seem like unexpected and hacky solutions. before we head down that road i wanted to ask:
  • is this is already a solved problem that i've missed?
  • is this issue already on the community's radar?
thanks in advance!

-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



-- 
Best Regards,
Yuval Itzchakov.


-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Till Rohrmann
Hi Vijay,

Flink usually writes first the checkpoint data to disk and then writes the pointer to the files to ZooKeeper. Hence, if you see a ZooKeeper entry, then the files should be there. I assume that there is no other process accessing and potentially removing files from the checkpoint directories, right?

Have you tried to run one of the latest Flink versions? Flink 1.6.2 is no longer actively supported by the community.

Cheers,
Till

On Fri, Oct 11, 2019 at 11:39 AM Vijay Bhaskar <[hidden email]> wrote:
Apart from these we have other environment and there check point worked fine in HA mode with complete cluster restart. But one of the job we are seeing an issue, in zookeeper the check point path is retrieved and its unable to find the check point path in persistent storage. I am wondering why this would happen first of all?  
Is there any sync issue between file writing over persistent path and file registration with HA service? For example check point has been registered in zookeeper but has not been written yet while restarting the cluster?  I suspect this kind of problem can happen. We are using flink 1.6.2 in production. Is this an issue already known before and fixed recently

Regards
Bhaskar

On Fri, Oct 11, 2019 at 2:08 PM Vijay Bhaskar <[hidden email]> wrote:
We are seeing below logs in production sometime ago, after that we stopped HA. Do you people think HA is enabled properly from the below logs?

Regards
Bhaskar

2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderelection.ZooKeeperLeaderElectionService  - Starting ZooKeeperLeaderElectionService ZooKeeperLeaderElectionService{leaderPath='/leader/dispatcher_lock'}.
2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderretrieval.ZooKeeperLeaderRetrievalService  - Starting ZooKeeperLeaderRetrievalService /leader/dispatcher_lock.
2019-09-24 17:40:20,975 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:20,976 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:23,976 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:23,977 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:26,982 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:26,983 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:29,988 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:29,988 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:32,994 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:32,995 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:36,000 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:36,001 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:39,006 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host

On Fri, Oct 11, 2019 at 9:39 AM Yun Tang <[hidden email]> wrote:
Hi Hao

It seems that I misunderstood the background of usage for your cases. High availability configuration targets for fault tolerance not for general development evolution. If you want to change your job topology, just follow the general rule to restore from savepoint/checkpoint, do not rely on HA to do job migration things. 

Best
Yun Tang

From: Hao Sun <[hidden email]>
Sent: Friday, October 11, 2019 8:33
To: Yun Tang <[hidden email]>
Cc: Vijay Bhaskar <[hidden email]>; Yang Wang <[hidden email]>; Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Yep I know that option. That's where get me confused as well. In a HA setup, where do I supply this option (allowNonRestoredState)?
This option requires a savepoint path when I start a flink job I remember. And HA does not require the path

Hao Sun


On Thu, Oct 10, 2019 at 11:16 AM Yun Tang <[hidden email]> wrote:
Just a minor supplement [hidden email], if you decided to drop a operator, don't forget to add --allowNonRestoredState (short: -n) option [1]



Best
Yun Tang


From: Vijay Bhaskar <[hidden email]>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <[hidden email]>
Cc: Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yun Tang <[hidden email]>; Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Thanks Yang. We will try and let you know if any issues arise

Regards
Bhaskar

On Thu, Oct 10, 2019 at 1:53 PM Yang Wang <[hidden email]> wrote:
@ Hao Sun,
I have made a confirmation that even we change parallelism and/or modify operators, add new operators,
the flink cluster could also recover from latest checkpoint.

@ Vijay
a) Some individual jobmanager/taskmanager crashed exceptionally(someother jobmanagers 
and taskmanagers are alive), it could recover from the latest checkpoint.
b) All jobmanagers and taskmanagers fails, it could still recover from the latest checkpoint if the cluster-id
is not changed. 

When we enable the HA, The meta of jobgraph and checkpoint is saved on zookeeper and the real files are save
on high-availability storage(HDFS). So when the flink application is submitted again with same cluster-id, it could
recover jobs and checkpoint from zookeeper. I think it has been supported for a long time. Maybe you could have a
try with flink-1.8 or 1.9.

Best,
Yang


Vijay Bhaskar <[hidden email]> 于2019年10月10日周四 下午2:26写道:
Thanks Yang and Sean. I have couple of questions:

1) Suppose the scenario of , bringing back entire cluster,
     a) In that case, at least one job manager out of HA group should be up and running right? or
     b) All the job managers fails, then also this works? In that case please let me know the procedure/share the documentation? 
         How to start from previous check point?
         What Flink version onwards this feature is stable?

Regards
Bhaskar


On Wed, Oct 9, 2019 at 8:51 AM Yang Wang <[hidden email]> wrote:
Hi Vijay,

If you are using HA solution, i think you do not need to specify the savepoint. Instead the checkpoint is used.
The checkpoint is done automatically and periodically based on your configuration.When the 
jobmanager/taskmanager fails or the whole cluster crashes, it could always recover from the latest
checkpoint. Does this meed your requirement?

Best,
Yang

Sean Hester <[hidden email]> 于2019年10月1日周二 上午1:47写道:
Vijay,

That is my understanding as well: the HA solution only solves the problem up to the point all job managers fail/restart at the same time. That's where my original concern was. 

But to Aleksandar and Yun's point, running in HA with 2 or 3 Job Managers per cluster--as long as they are all deployed to separate GKE nodes--would provide a very high uptime/low failure rate, at least on paper. It's a promising enough option that we're going to run in HA for a month or two and monitor results before we put in any extra work to customize the savepoint start-up behavior.

On Fri, Sep 27, 2019 at 2:24 AM Vijay Bhaskar <[hidden email]> wrote:
I don't think HA will help to recover from cluster crash, for that we should take periodic savepoint right? Please correct me in case i am wrong

Regards
Bhaskar

On Fri, Sep 27, 2019 at 11:48 AM Vijay Bhaskar <[hidden email]> wrote:
Suppose my cluster got crashed and need to bring up the entire cluster back? Does HA still helps to run the cluster from latest save point? 

Regards
Bhaskar

On Thu, Sep 26, 2019 at 7:44 PM Sean Hester <[hidden email]> wrote:
thanks to everyone for all the replies.

i think the original concern here with "just" relying on the HA option is that there are some disaster recovery and data center migration use cases where the continuity of the job managers is difficult to preserve. but those are admittedly very edgy use cases. i think it's definitely worth reviewing the SLAs with our site reliability engineers to see how likely it would be to completely lose all job managers under an HA configuration. that small a risk might be acceptable/preferable to a one-off solution.

@Aleksander, would love to learn more about Zookeeper-less HA. i think i spotted a thread somewhere between Till and someone (perhaps you) about that. feel free to DM me.

thanks again to everyone!

On Thu, Sep 26, 2019 at 7:32 AM Yang Wang <[hidden email]> wrote:
Hi, Aleksandar

Savepoint option in standalone job cluster is optional. If you want to always recover 
from the latest checkpoint, just as Aleksandar and Yun Tang said you could use the 
high-availability configuration. Make sure the cluster-id is not changed, i think the job 
could recover both at exceptionally crash and restart by expectation.

[hidden email], we are also have an zookeeper-less high-availability implementation[1].
Maybe we could have some discussion and contribute this useful feature to the community.


Best,
Yang

Aleksandar Mastilovic <[hidden email]> 于2019年9月26日周四 上午4:11写道:
Would you guys (Flink devs) be interested in our solution for zookeeper-less HA? I could ask the managers how they feel about open-sourcing the improvement.

On Sep 25, 2019, at 11:49 AM, Yun Tang <[hidden email]> wrote:

As Aleksandar said, k8s with HA configuration could solve your problem. There already have some discussion about how to implement such HA in k8s if we don't have a zookeeper service: FLINK-11105 [1] and FLINK-12884 [2]. Currently, you might only have to choose zookeeper as high-availability service.


Best
Yun Tang

From: Aleksandar Mastilovic <[hidden email]>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <[hidden email]>
Cc: Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Can’t you simply use JobManager in HA mode? It would pick up where it left off if you don’t provide a Savepoint.

On Sep 25, 2019, at 6:07 AM, Sean Hester <[hidden email]> wrote:

thanks for all replies! i'll definitely take a look at the Flink k8s Operator project.

i'll try to restate the issue to clarify. this issue is specific to starting a job from a savepoint in job-cluster mode. in these cases the Job Manager container is configured to run a single Flink job at start-up. the savepoint needs to be provided as an argument to the entrypoint. the Flink documentation for this approach is here:


the issue is that taking this approach means that the job will always start from the savepoint provided as the start argument in the Kubernetes YAML. this includes unplanned restarts of the job manager, but we'd really prefer any unplanned restarts resume for the most recent checkpoint instead of restarting from the configured savepoint. so in a sense we want the savepoint argument to be transient, only being used during the initial deployment, but this runs counter to the design of Kubernetes which always wants to restore a deployment to the "goal state" as defined in the YAML.

i hope this helps. if you want more details please let me know, and thanks again for your time.


On Tue, Sep 24, 2019 at 1:09 PM Hao Sun <[hidden email]> wrote:
I think I overlooked it. Good point. I am using Redis to save the path to my savepoint, I might be able to set a TTL to avoid such issue.

Hao Sun


On Tue, Sep 24, 2019 at 9:54 AM Yuval Itzchakov <[hidden email]> wrote:
Hi Hao,

I think he's exactly talking about the usecase where the JM/TM restart and they come back up from the latest savepoint which might be stale by that time.

On Tue, 24 Sep 2019, 19:24 Hao Sun, <[hidden email]> wrote:
We always make a savepoint before we shutdown the job-cluster. So the savepoint is always the latest. When we fix a bug or change the job graph, it can resume well.
We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM, uncaught exception, etc.

Maybe I do not understand your use case well, I do not see a need to start from checkpoint after a bug fix.
From what I know, currently you can use checkpoint as a savepoint as well

Hao Sun


On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
AFAIK there's currently nothing implemented to solve this problem, but working on a possible fix can be implemented on top of https://github.com/lyft/flinkk8soperator which already has a pretty fancy state machine for rolling upgrades. I'd love to be involved as this is an issue I've been thinking about as well.

Yuval

On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]> wrote:
hi all--we've run into a gap (knowledge? design? tbd?) for our use cases when deploying Flink jobs to start from savepoints using the job-cluster mode in Kubernetes.

we're running a ~15 different jobs, all in job-cluster mode, using a mix of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are all long-running streaming jobs, all essentially acting as microservices. we're using Helm charts to configure all of our deployments.

we have a number of use cases where we want to restart jobs from a savepoint to replay recent events, i.e. when we've enhanced the job logic or fixed a bug. but after the deployment we want to have the job resume it's "long-running" behavior, where any unplanned restarts resume from the latest checkpoint.

the issue we run into is that any obvious/standard/idiomatic Kubernetes deployment includes the savepoint argument in the configuration. if the Job Manager container(s) have an unplanned restart, when they come back up they will start from the savepoint instead of resuming from the latest checkpoint. everything is working as configured, but that's not exactly what we want. we want the savepoint argument to be transient somehow (only used during the initial deployment), but Kubernetes doesn't really support the concept of transient configuration.

i can see a couple of potential solutions that either involve custom code in the jobs or custom logic in the container (i.e. a custom entrypoint script that records that the configured savepoint has already been used in a file on a persistent volume or GCS, and potentially when/why/by which deployment). but these seem like unexpected and hacky solutions. before we head down that road i wanted to ask:
  • is this is already a solved problem that i've missed?
  • is this issue already on the community's radar?
thanks in advance!

-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



-- 
Best Regards,
Yuval Itzchakov.


-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Vijay Bhaskar
Thanks you till. We will try to shift to latest flink version.

Regards
Bhaskar

On Mon, Oct 14, 2019 at 7:43 PM Till Rohrmann <[hidden email]> wrote:
Hi Vijay,

Flink usually writes first the checkpoint data to disk and then writes the pointer to the files to ZooKeeper. Hence, if you see a ZooKeeper entry, then the files should be there. I assume that there is no other process accessing and potentially removing files from the checkpoint directories, right?

Have you tried to run one of the latest Flink versions? Flink 1.6.2 is no longer actively supported by the community.

Cheers,
Till

On Fri, Oct 11, 2019 at 11:39 AM Vijay Bhaskar <[hidden email]> wrote:
Apart from these we have other environment and there check point worked fine in HA mode with complete cluster restart. But one of the job we are seeing an issue, in zookeeper the check point path is retrieved and its unable to find the check point path in persistent storage. I am wondering why this would happen first of all?  
Is there any sync issue between file writing over persistent path and file registration with HA service? For example check point has been registered in zookeeper but has not been written yet while restarting the cluster?  I suspect this kind of problem can happen. We are using flink 1.6.2 in production. Is this an issue already known before and fixed recently

Regards
Bhaskar

On Fri, Oct 11, 2019 at 2:08 PM Vijay Bhaskar <[hidden email]> wrote:
We are seeing below logs in production sometime ago, after that we stopped HA. Do you people think HA is enabled properly from the below logs?

Regards
Bhaskar

2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderelection.ZooKeeperLeaderElectionService  - Starting ZooKeeperLeaderElectionService ZooKeeperLeaderElectionService{leaderPath='/leader/dispatcher_lock'}.
2019-09-24 17:40:17,675 INFO  org.apache.flink.runtime.leaderretrieval.ZooKeeperLeaderRetrievalService  - Starting ZooKeeperLeaderRetrievalService /leader/dispatcher_lock.
2019-09-24 17:40:20,975 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:20,976 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:23,976 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:23,977 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:26,982 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:26,983 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:29,988 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:29,988 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:32,994 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:32,995 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:36,000 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host
2019-09-24 17:40:36,001 WARN  akka.remote.ReliableDeliverySupervisor                        - Association with remote system [akka.tcp:[hidden email]:6123] has failed, address is now gated for [50] ms. Reason: [Association failed with [akka.tcp:[hidden email]:6123]] Caused by: [No route to host]
2019-09-24 17:40:39,006 WARN  akka.remote.transport.netty.NettyTransport                    - Remote connection to [null] failed with java.net.NoRouteToHostException: No route to host

On Fri, Oct 11, 2019 at 9:39 AM Yun Tang <[hidden email]> wrote:
Hi Hao

It seems that I misunderstood the background of usage for your cases. High availability configuration targets for fault tolerance not for general development evolution. If you want to change your job topology, just follow the general rule to restore from savepoint/checkpoint, do not rely on HA to do job migration things. 

Best
Yun Tang

From: Hao Sun <[hidden email]>
Sent: Friday, October 11, 2019 8:33
To: Yun Tang <[hidden email]>
Cc: Vijay Bhaskar <[hidden email]>; Yang Wang <[hidden email]>; Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Yep I know that option. That's where get me confused as well. In a HA setup, where do I supply this option (allowNonRestoredState)?
This option requires a savepoint path when I start a flink job I remember. And HA does not require the path

Hao Sun


On Thu, Oct 10, 2019 at 11:16 AM Yun Tang <[hidden email]> wrote:
Just a minor supplement [hidden email], if you decided to drop a operator, don't forget to add --allowNonRestoredState (short: -n) option [1]



Best
Yun Tang


From: Vijay Bhaskar <[hidden email]>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <[hidden email]>
Cc: Sean Hester <[hidden email]>; Aleksandar Mastilovic <[hidden email]>; Yun Tang <[hidden email]>; Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Thanks Yang. We will try and let you know if any issues arise

Regards
Bhaskar

On Thu, Oct 10, 2019 at 1:53 PM Yang Wang <[hidden email]> wrote:
@ Hao Sun,
I have made a confirmation that even we change parallelism and/or modify operators, add new operators,
the flink cluster could also recover from latest checkpoint.

@ Vijay
a) Some individual jobmanager/taskmanager crashed exceptionally(someother jobmanagers 
and taskmanagers are alive), it could recover from the latest checkpoint.
b) All jobmanagers and taskmanagers fails, it could still recover from the latest checkpoint if the cluster-id
is not changed. 

When we enable the HA, The meta of jobgraph and checkpoint is saved on zookeeper and the real files are save
on high-availability storage(HDFS). So when the flink application is submitted again with same cluster-id, it could
recover jobs and checkpoint from zookeeper. I think it has been supported for a long time. Maybe you could have a
try with flink-1.8 or 1.9.

Best,
Yang


Vijay Bhaskar <[hidden email]> 于2019年10月10日周四 下午2:26写道:
Thanks Yang and Sean. I have couple of questions:

1) Suppose the scenario of , bringing back entire cluster,
     a) In that case, at least one job manager out of HA group should be up and running right? or
     b) All the job managers fails, then also this works? In that case please let me know the procedure/share the documentation? 
         How to start from previous check point?
         What Flink version onwards this feature is stable?

Regards
Bhaskar


On Wed, Oct 9, 2019 at 8:51 AM Yang Wang <[hidden email]> wrote:
Hi Vijay,

If you are using HA solution, i think you do not need to specify the savepoint. Instead the checkpoint is used.
The checkpoint is done automatically and periodically based on your configuration.When the 
jobmanager/taskmanager fails or the whole cluster crashes, it could always recover from the latest
checkpoint. Does this meed your requirement?

Best,
Yang

Sean Hester <[hidden email]> 于2019年10月1日周二 上午1:47写道:
Vijay,

That is my understanding as well: the HA solution only solves the problem up to the point all job managers fail/restart at the same time. That's where my original concern was. 

But to Aleksandar and Yun's point, running in HA with 2 or 3 Job Managers per cluster--as long as they are all deployed to separate GKE nodes--would provide a very high uptime/low failure rate, at least on paper. It's a promising enough option that we're going to run in HA for a month or two and monitor results before we put in any extra work to customize the savepoint start-up behavior.

On Fri, Sep 27, 2019 at 2:24 AM Vijay Bhaskar <[hidden email]> wrote:
I don't think HA will help to recover from cluster crash, for that we should take periodic savepoint right? Please correct me in case i am wrong

Regards
Bhaskar

On Fri, Sep 27, 2019 at 11:48 AM Vijay Bhaskar <[hidden email]> wrote:
Suppose my cluster got crashed and need to bring up the entire cluster back? Does HA still helps to run the cluster from latest save point? 

Regards
Bhaskar

On Thu, Sep 26, 2019 at 7:44 PM Sean Hester <[hidden email]> wrote:
thanks to everyone for all the replies.

i think the original concern here with "just" relying on the HA option is that there are some disaster recovery and data center migration use cases where the continuity of the job managers is difficult to preserve. but those are admittedly very edgy use cases. i think it's definitely worth reviewing the SLAs with our site reliability engineers to see how likely it would be to completely lose all job managers under an HA configuration. that small a risk might be acceptable/preferable to a one-off solution.

@Aleksander, would love to learn more about Zookeeper-less HA. i think i spotted a thread somewhere between Till and someone (perhaps you) about that. feel free to DM me.

thanks again to everyone!

On Thu, Sep 26, 2019 at 7:32 AM Yang Wang <[hidden email]> wrote:
Hi, Aleksandar

Savepoint option in standalone job cluster is optional. If you want to always recover 
from the latest checkpoint, just as Aleksandar and Yun Tang said you could use the 
high-availability configuration. Make sure the cluster-id is not changed, i think the job 
could recover both at exceptionally crash and restart by expectation.

[hidden email], we are also have an zookeeper-less high-availability implementation[1].
Maybe we could have some discussion and contribute this useful feature to the community.


Best,
Yang

Aleksandar Mastilovic <[hidden email]> 于2019年9月26日周四 上午4:11写道:
Would you guys (Flink devs) be interested in our solution for zookeeper-less HA? I could ask the managers how they feel about open-sourcing the improvement.

On Sep 25, 2019, at 11:49 AM, Yun Tang <[hidden email]> wrote:

As Aleksandar said, k8s with HA configuration could solve your problem. There already have some discussion about how to implement such HA in k8s if we don't have a zookeeper service: FLINK-11105 [1] and FLINK-12884 [2]. Currently, you might only have to choose zookeeper as high-availability service.


Best
Yun Tang

From: Aleksandar Mastilovic <[hidden email]>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <[hidden email]>
Cc: Hao Sun <[hidden email]>; Yuval Itzchakov <[hidden email]>; user <[hidden email]>
Subject: Re: Challenges Deploying Flink With Savepoints On Kubernetes
 
Can’t you simply use JobManager in HA mode? It would pick up where it left off if you don’t provide a Savepoint.

On Sep 25, 2019, at 6:07 AM, Sean Hester <[hidden email]> wrote:

thanks for all replies! i'll definitely take a look at the Flink k8s Operator project.

i'll try to restate the issue to clarify. this issue is specific to starting a job from a savepoint in job-cluster mode. in these cases the Job Manager container is configured to run a single Flink job at start-up. the savepoint needs to be provided as an argument to the entrypoint. the Flink documentation for this approach is here:


the issue is that taking this approach means that the job will always start from the savepoint provided as the start argument in the Kubernetes YAML. this includes unplanned restarts of the job manager, but we'd really prefer any unplanned restarts resume for the most recent checkpoint instead of restarting from the configured savepoint. so in a sense we want the savepoint argument to be transient, only being used during the initial deployment, but this runs counter to the design of Kubernetes which always wants to restore a deployment to the "goal state" as defined in the YAML.

i hope this helps. if you want more details please let me know, and thanks again for your time.


On Tue, Sep 24, 2019 at 1:09 PM Hao Sun <[hidden email]> wrote:
I think I overlooked it. Good point. I am using Redis to save the path to my savepoint, I might be able to set a TTL to avoid such issue.

Hao Sun


On Tue, Sep 24, 2019 at 9:54 AM Yuval Itzchakov <[hidden email]> wrote:
Hi Hao,

I think he's exactly talking about the usecase where the JM/TM restart and they come back up from the latest savepoint which might be stale by that time.

On Tue, 24 Sep 2019, 19:24 Hao Sun, <[hidden email]> wrote:
We always make a savepoint before we shutdown the job-cluster. So the savepoint is always the latest. When we fix a bug or change the job graph, it can resume well.
We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM, uncaught exception, etc.

Maybe I do not understand your use case well, I do not see a need to start from checkpoint after a bug fix.
From what I know, currently you can use checkpoint as a savepoint as well

Hao Sun


On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
AFAIK there's currently nothing implemented to solve this problem, but working on a possible fix can be implemented on top of https://github.com/lyft/flinkk8soperator which already has a pretty fancy state machine for rolling upgrades. I'd love to be involved as this is an issue I've been thinking about as well.

Yuval

On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]> wrote:
hi all--we've run into a gap (knowledge? design? tbd?) for our use cases when deploying Flink jobs to start from savepoints using the job-cluster mode in Kubernetes.

we're running a ~15 different jobs, all in job-cluster mode, using a mix of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are all long-running streaming jobs, all essentially acting as microservices. we're using Helm charts to configure all of our deployments.

we have a number of use cases where we want to restart jobs from a savepoint to replay recent events, i.e. when we've enhanced the job logic or fixed a bug. but after the deployment we want to have the job resume it's "long-running" behavior, where any unplanned restarts resume from the latest checkpoint.

the issue we run into is that any obvious/standard/idiomatic Kubernetes deployment includes the savepoint argument in the configuration. if the Job Manager container(s) have an unplanned restart, when they come back up they will start from the savepoint instead of resuming from the latest checkpoint. everything is working as configured, but that's not exactly what we want. we want the savepoint argument to be transient somehow (only used during the initial deployment), but Kubernetes doesn't really support the concept of transient configuration.

i can see a couple of potential solutions that either involve custom code in the jobs or custom logic in the container (i.e. a custom entrypoint script that records that the configured savepoint has already been used in a file on a persistent volume or GCS, and potentially when/why/by which deployment). but these seem like unexpected and hacky solutions. before we head down that road i wanted to ask:
  • is this is already a solved problem that i've missed?
  • is this issue already on the community's radar?
thanks in advance!

-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



-- 
Best Regards,
Yuval Itzchakov.


-- 
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 



--
Sean Hester | Senior Staff Software Engineer | m. 404-828-0865
3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305 

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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Matt Magsombol
In reply to this post by Hao Sun
I'm not the original poster, but I'm running into this same issue. What you just described is exactly what I want. I presume you guys are using some variant of this helm https://github.com/docker-flink/examples/tree/master/helm/flink to configure your k8s cluster? I'm also assuming that this cluster is running as a job cluster and not a session cluster right?
If so, how did you guys set up the deployments.yaml file such that it picks up the latest savepoint from a savepoint directory ( and what happens if that savepoint directory is empty? This is for cases when we're starting a new cluster, new job from scratch and there's no need to recover from previous savepoint ).

On 2019/09/24 16:23:52, Hao Sun <[hidden email]> wrote:

> We always make a savepoint before we shutdown the job-cluster. So the
> savepoint is always the latest. When we fix a bug or change the job graph,
> it can resume well.
> We only use checkpoints for unplanned downtime, e.g. K8S killed JM/TM,
> uncaught exception, etc.
>
> Maybe I do not understand your use case well, I do not see a need to start
> from checkpoint after a bug fix.
> From what I know, currently you can use checkpoint as a savepoint as well
>
> Hao Sun
>
>
> On Tue, Sep 24, 2019 at 7:48 AM Yuval Itzchakov <[hidden email]> wrote:
>
> > AFAIK there's currently nothing implemented to solve this problem, but
> > working on a possible fix can be implemented on top of
> > https://github.com/lyft/flinkk8soperator
> > <https://github.com/lyft/flinkk8soperator> which already
> > has a pretty fancy state machine for rolling upgrades. I'd love to be
> > involved as this is an issue I've been thinking about as well.
> >
> > Yuval
> >
> > On Tue, Sep 24, 2019 at 5:02 PM Sean Hester <[hidden email]>
> > wrote:
> >
> >> hi all--we've run into a gap (knowledge? design? tbd?) for our use cases
> >> when deploying Flink jobs to start from savepoints using the job-cluster
> >> mode in Kubernetes.
> >>
> >> we're running a ~15 different jobs, all in job-cluster mode, using a mix
> >> of Flink 1.8.1 and 1.9.0, under GKE (Google Kubernetes Engine). these are
> >> all long-running streaming jobs, all essentially acting as microservices.
> >> we're using Helm charts to configure all of our deployments.
> >>
> >> we have a number of use cases where we want to restart jobs from a
> >> savepoint to replay recent events, i.e. when we've enhanced the job logic
> >> or fixed a bug. but after the deployment we want to have the job resume
> >> it's "long-running" behavior, where any unplanned restarts resume from the
> >> latest checkpoint.
> >>
> >> the issue we run into is that any obvious/standard/idiomatic Kubernetes
> >> deployment includes the savepoint argument in the configuration. if the Job
> >> Manager container(s) have an unplanned restart, when they come back up they
> >> will start from the savepoint instead of resuming from the latest
> >> checkpoint. everything is working as configured, but that's not exactly
> >> what we want. we want the savepoint argument to be transient somehow (only
> >> used during the initial deployment), but Kubernetes doesn't really support
> >> the concept of transient configuration.
> >>
> >> i can see a couple of potential solutions that either involve custom code
> >> in the jobs or custom logic in the container (i.e. a custom entrypoint
> >> script that records that the configured savepoint has already been used in
> >> a file on a persistent volume or GCS, and potentially when/why/by which
> >> deployment). but these seem like unexpected and hacky solutions. before we
> >> head down that road i wanted to ask:
> >>
> >>    - is this is already a solved problem that i've missed?
> >>    - is this issue already on the community's radar?
> >>
> >> thanks in advance!
> >>
> >> --
> >> *Sean Hester* | Senior Staff Software Engineer | m. 404-828-0865
> >> 3525 Piedmont Rd. NE, Building 6, Suite 500, Atlanta, GA 30305
> >> <http://www.bettercloud.com>
> >> <http://www.bettercloud.com>
> >> *Altitude 2019 in San Francisco | Sept. 23 - 25*
> >> It’s not just an IT conference, it’s “a complete learning and networking
> >> experience” <https://altitude.bettercloud.com/?utm_source=gmail&utm_medium=signature&utm_campaign=2019-altitude>
> >>
> >>
> >
> > --
> > Best Regards,
> > Yuval Itzchakov.
> >
>
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Re: Challenges Deploying Flink With Savepoints On Kubernetes

vishalovercome
In reply to this post by Yun Tang
I'm not sure if this addresses the original concern. For instance consider
this sequence:

1. Job starts from savepoint
2. Job creates a few checkpoints
3. Job manager (just one in kubernetes) crashes and restarts with the
commands specified in the kubernetes manifest which has the savepoint path

Will Zookeeper based HA ensure that this savepoint path will be ignored?

I've asked this and various other questions here -
http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Will-job-manager-restarts-lead-to-repeated-savepoint-restoration-tp40188.html



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Re: Challenges Deploying Flink With Savepoints On Kubernetes

Till Rohrmann
Flink should try to pick the latest checkpoint and will only use the savepoint if no newer checkpoint could be found.

Cheers,
Till

On Wed, Dec 16, 2020 at 10:13 PM vishalovercome <[hidden email]> wrote:
I'm not sure if this addresses the original concern. For instance consider
this sequence:

1. Job starts from savepoint
2. Job creates a few checkpoints
3. Job manager (just one in kubernetes) crashes and restarts with the
commands specified in the kubernetes manifest which has the savepoint path

Will Zookeeper based HA ensure that this savepoint path will be ignored?

I've asked this and various other questions here -
http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Will-job-manager-restarts-lead-to-repeated-savepoint-restoration-tp40188.html



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Re: Challenges Deploying Flink With Savepoints On Kubernetes

vishalovercome
Thanks for your reply!

What I have seen is that the job terminates when there's intermittent loss
of connectivity with zookeeper. This is in-fact the most common reason why
our jobs are terminating at this point. Worse, it's unable to restore from
checkpoint during some (not all) of these terminations. Under these
scenarios, won't the job try to recover from a savepoint?

I've gone through various tickets reporting stability issues due to
zookeeper that you've mentioned you intend to resolve soon. But until the
zookeeper based HA is stable, should we assume that it will repeatedly
restore from savepoints? I would rather rely on kafka offsets to resume
where it left off rather than savepoints.




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