HA with HDFS question

[Steven Nelson]

First off, I am new to using HDFS to store things, so expect stupid questions.

I am working on hardening our Flink cluster for production usage. This includes setting up an HA flink cluster, saving checkpoint and savepoints to a central location etc. I have a functioning HDFS setup inside an HA Kubernetes cluster. We have successfully stored checkpoint data in the HDFS directory.

When we specify the location for the HDFS savepoints/checkpoints/HA save locations we specify the a single namenode in the url. My question is how do we implement failover in the event that namenode fails? We looked at putting the namenodes behind a load balancer, except the backup nodes attempt to respond to writes (and fail). I figure I am missing something simple.

-Steve

[Andrey Zagrebin]

Hi Steve,

I think your question is specific to HDFS HA setup.
Flink HA addresses failover issues only for job manager and job meta state.
The storage layer for savepoints/checkpoints and its failover are responsibility of HDFS deployment.
Flink uses HDFS as external system, available over location url.
I am not an expert on HDFS HA deployment. You could have a look into hadoop docs [1].

Best,
Andrey

[1] https://hadoop.apache.org/docs/r2.7.1/hadoop-project-dist/hadoop-hdfs/HDFSHighAvailabilityWithQJM.html

> On 21 Dec 2018, at 21:48, Steven Nelson <[hidden email]> wrote:
>
> First off, I am new to using HDFS to store things, so expect stupid questions.
>
> I am working on hardening our Flink cluster for production usage. This includes setting up an HA flink cluster, saving checkpoint and savepoints to a central location etc. I have a functioning HDFS setup inside an HA Kubernetes cluster. We have successfully stored checkpoint data in the HDFS directory.
>
> When we specify the location for the HDFS savepoints/checkpoints/HA save locations we specify the a single namenode in the url. My question is how do we implement failover in the event that namenode fails? We looked at putting the namenodes behind a load balancer, except the backup nodes attempt to respond to writes (and fail). I figure I am missing something simple.
>
> -Steve

[Steven Nelson]

Well, I have a fully functioning HDFS HA setup via a helm chart. My question is more about how to specify the hdfs nodename in such a way so that if a name node fails it communicates with the new active name node automatically. Swapnil mentioned configuring nameservice for hdfs namenode and I was looking for clarification on that.

-Steve

On Mon, Dec 24, 2018 at 8:20 AM Andrey Zagrebin <[hidden email]> wrote:

Hi Steve,

I think your question is specific to HDFS HA setup.
Flink HA addresses failover issues only for job manager and job meta state.
The storage layer for savepoints/checkpoints and its failover are responsibility of HDFS deployment.
Flink uses HDFS as external system, available over location url.
I am not an expert on HDFS HA deployment. You could have a look into hadoop docs [1].

Best,
Andrey

[1] https://hadoop.apache.org/docs/r2.7.1/hadoop-project-dist/hadoop-hdfs/HDFSHighAvailabilityWithQJM.html

> On 21 Dec 2018, at 21:48, Steven Nelson <[hidden email]> wrote:
>
> First off, I am new to using HDFS to store things, so expect stupid questions.
>
> I am working on hardening our Flink cluster for production usage. This includes setting up an HA flink cluster, saving checkpoint and savepoints to a central location etc. I have a functioning HDFS setup inside an HA Kubernetes cluster. We have successfully stored checkpoint data in the HDFS directory.
>
> When we specify the location for the HDFS savepoints/checkpoints/HA save locations we specify the a single namenode in the url. My question is how do we implement failover in the event that namenode fails? We looked at putting the namenodes behind a load balancer, except the backup nodes attempt to respond to writes (and fail). I figure I am missing something simple.
>
> -Steve