Re: Task manager not able to rejoin job manager after network hicup

Posted by Till Rohrmann on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Task-manager-not-able-to-rejoin-job-manager-after-network-hicup-tp18525p18567.html

Actually, I remembered why we didn't enable it by default. The problem with this feature is the following: In case of a JM failover it could happen that all TMs think they got quarantined because the JM ActorSystem is no longer reachable. Therefore, you could see a lot of TM restarts in this case where it is not really necessary. There is actually a PR which removes the Akka based heartbeats on the TM side [1] which would mitigate the problem. But this PR never got merged.

Given that the user can activate this feature and that it should no longer be present with Flink 1.5, I think we should keep it as it is. What do you think?

[1] https://github.com/apache/flink/pull/2742

Cheers,

Till

On Mon, Feb 26, 2018 at 4:33 PM, Till Rohrmann <[hidden email]> wrote:

Hi,

it is correct that once a Flink component gets quarantined, e.g. lost ActorSystem message or heartbeat timeout, it will never be able to talk to the quarantined or quarantining system. The only solution is to restart the respective component. In order to do this automatically, we introduced the `taskmanager.exit-on-fatal-akka-error` configuration option. Since not all systems are able to restart components, e.g. the standalone mode, it is disabled by default.

However, given that the component won't be reachable if it is kept alive, I guess you're right that we should turn this feature on by default. I'll apply the fix.

With Flink 1.5 this should no longer be a problem, since we no longer rely on Akka's heartbeating. Instead we use our own heartbeats which won't quarantine an ActorSystem.

Cheers,

Till

On Sat, Feb 24, 2018 at 9:34 PM, jelmer <[hidden email]> wrote:

I don't think its entirely the same thing. It seems to be that by design once a worker misses a heartbeat for whatever reason , be it a network hicup or a long stop the world garbage collect etc etc, it gets quarantined and it will not recover from that until it is restarted.

Which is what the post by till in the thread you linked seems to indicate.

I assumed that a system like flink would be able to recover from this and that if it does not that its a bug

Your problem seems to be that for some reason flink misses the heartbeats under heavy load

I just simulated missing a heartbeat by blocking traffic to the job manager

On 24 February 2018 at 15:57, ashish pok <[hidden email]> wrote:

We see the same in 1.4. I dont think we could see this in 1.3. I had started a thread a while back on this. Till asked for more details. I havent had a chance to get back to him on this. If you can repro this easily perhaps you can get to it faster. I will find the thread and resend.

Thanks,

-- Ashish

On Fri, Feb 23, 2018 at 9:56 AM, jelmer

<[hidden email]> wrote:

We found out there's a taskmanager.exit-on-fatal-akka-error property that will restart flink in this situation but it is not enabled by default and that feels like a rather blunt tool. I expect systems like this to be more resilient to this

On 23 February 2018 at 14:42, Aljoscha Krettek <[hidden email]> wrote:

@Till Is this the expected behaviour or do you suspect something could be going wrong?

On 23. Feb 2018, at 08:59, jelmer <[hidden email]> wrote:

We've observed on our flink 1.4.0 setup that if for some reason the networking between the task manager and the job manager gets disrupted then the task manager is never able to reconnect.

You'll end up with messages like this getting printed to the log repeatedly

Trying to register at JobManager akka.tcp://flink@jobmanager: 6123/user/jobmanager (attempt 17, timeout: 30000 milliseconds)
Quarantined address [akka.tcp://flink@jobmanager: 6123] is still unreachable or has not been restarted. Keeping it quarantined.

Or alternatively

Tried to associate with unreachable remote address [akka.tcp://flink@jobmanager: 6123]. Address is now gated for 5000 ms, all messages to this address will be delivered to dead letters. Reason: [The remote system has quarantined this system. No further associations to the remote system are possible until this system is restarted.

But it never recovers until you either restart the job manager or the task manager

I was able to successfully reproduce this behaviour in two docker containers here :

https://github.com/jelmerk/ flink-worker-not-rejoining 

Has anyone else seen this problem ?