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From Yun Tang <myas...@live.com>
Subject Re: Challenges Deploying Flink With Savepoints On Kubernetes
Date Thu, 10 Oct 2019 18:16:20 GMT
Just a minor supplement @Hao Sun<mailto:hasun@zendesk.com>, if you decided to drop a
operator, don't forget to add --allowNonRestoredState (short: -n) option [1]


[1] https://ci.apache.org/projects/flink/flink-docs-stable/ops/state/savepoints.html#allowing-non-restored-state

Best
Yun Tang

________________________________
From: Vijay Bhaskar <bhaskar.ebay77@gmail.com>
Sent: Thursday, October 10, 2019 19:24
To: Yang Wang <danrtsey.wy@gmail.com>
Cc: Sean Hester <sean.hester@bettercloud.com>; Aleksandar Mastilovic <amastilovic@sightmachine.com>;
Yun Tang <myasuka@live.com>; Hao Sun <hasun@zendesk.com>; Yuval Itzchakov <yuvalos@gmail.com>;
user <user@flink.apache.org>
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 <danrtsey.wy@gmail.com<mailto:danrtsey.wy@gmail.com>>
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 <bhaskar.ebay77@gmail.com<mailto:bhaskar.ebay77@gmail.com>> 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 <danrtsey.wy@gmail.com<mailto:danrtsey.wy@gmail.com>>
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 <sean.hester@bettercloud.com<mailto:sean.hester@bettercloud.com>>
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 <bhaskar.ebay77@gmail.com<mailto:bhaskar.ebay77@gmail.com>>
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 <bhaskar.ebay77@gmail.com<mailto:bhaskar.ebay77@gmail.com>>
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 <sean.hester@bettercloud.com<mailto:sean.hester@bettercloud.com>>
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 <danrtsey.wy@gmail.com<mailto:danrtsey.wy@gmail.com>>
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.

@Aleksandar Mastilovic<mailto:amastilovic@sightmachine.com>, 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.

[1]. https://docs.google.com/document/d/1Z-VdJlPPEQoWT1WLm5woM4y0bFep4FrgdJ9ipQuRv8g/edit

Best,
Yang

Aleksandar Mastilovic <amastilovic@sightmachine.com<mailto:amastilovic@sightmachine.com>>
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 <myasuka@live.com<mailto:myasuka@live.com>>
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.

[1] https://issues.apache.org/jira/browse/FLINK-11105
[2] https://issues.apache.org/jira/browse/FLINK-12884

Best
Yun Tang
________________________________
From: Aleksandar Mastilovic <amastilovic@sightmachine.com<mailto:amastilovic@sightmachine.com>>
Sent: Thursday, September 26, 2019 1:57
To: Sean Hester <sean.hester@bettercloud.com<mailto:sean.hester@bettercloud.com>>
Cc: Hao Sun <hasun@zendesk.com<mailto:hasun@zendesk.com>>; Yuval Itzchakov <yuvalos@gmail.com<mailto:yuvalos@gmail.com>>;
user <user@flink.apache.org<mailto:user@flink.apache.org>>
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 <sean.hester@bettercloud.com<mailto:sean.hester@bettercloud.com>>
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:

https://github.com/apache/flink/tree/master/flink-container/kubernetes#resuming-from-a-savepoint

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 <hasun@zendesk.com<mailto:hasun@zendesk.com>>
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 <yuvalos@gmail.com<mailto:yuvalos@gmail.com>>
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, <hasun@zendesk.com<mailto:hasun@zendesk.com>>
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 <yuvalos@gmail.com<mailto:yuvalos@gmail.com>>
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 <sean.hester@bettercloud.com<mailto:sean.hester@bettercloud.com>>
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/>[https://www.bettercloud.com/monitor/wp-content/uploads/sites/3/2016/12/bettercloud-emaillogo.png]<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.


--
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/>[https://www.bettercloud.com/monitor/wp-content/uploads/sites/3/2016/12/bettercloud-emaillogo.png]<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>



--
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>[https://www.bettercloud.com/monitor/wp-content/uploads/sites/3/2016/12/bettercloud-emaillogo.png]<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>



--
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>[https://www.bettercloud.com/monitor/wp-content/uploads/sites/3/2016/12/bettercloud-emaillogo.png]<http://www.bettercloud.com>
Introducing the BetterCloud Integration Center
Automate actions across every app and own SaaSOps<https://www.bettercloud.com/integrations-webinar/?utm_source=gmail&utm_medium=signature&utm_campaign=2019-integration-center>


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