[jira] [Commented] (YARN-8080) YARN native service should support component restart policy

["Suma Shivaprasad (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/YARN-8080?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16463097#comment-16463097 ] 

Suma Shivaprasad commented on YARN-8080:
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Thanks [~gsaha] for reviews and offline discussions on the patch.  While testing the flex scenarios as suggested by [~gsaha] with the patch, ran into the following issues.


What does flexing  up/down a component with "restart_policy" : NEVER/ "restart_policy: ON_FAILURE mean?

Consider the following scenario where a component has 4 instances configured and restart_policy="NEVER". Assume that 2 of these containers have exited successfully after execution and 2 are still running.

1. Flex up
Now if the user , flexes the number of containers to 3, should we even support flexing up of containers in this case? For eg: It could be a Tensorflow DAG - YARN-8135 in which flexing up may or may not make sense unless the Tensorflow client needs more resources is able to make use of the newly allocated containers  (like the dynamic allocation usecase in SPARK ).  [~leftnoteasy] could comment on this. We could add support for a flag in the YARN service spec to disallow/allow flexing for services and user can choose to disallow this for specific apps.

2. Flex down
Also flex down for such services needs to consider the current number of running containers (instead of configured number of containers which is the behaviour currently) and scale them down accordingly. For eg: if component instance during flex is set to 1, bring down the number of running containers to 1.

[~billie.rinaldi] [~leftnoteasy] [~gsaha] [~eyang] Thoughts?









> YARN native service should support component restart policy
> -----------------------------------------------------------
>
>                 Key: YARN-8080
>                 URL: https://issues.apache.org/jira/browse/YARN-8080
>             Project: Hadoop YARN
>          Issue Type: Task
>            Reporter: Wangda Tan
>            Assignee: Suma Shivaprasad
>            Priority: Critical
>         Attachments: YARN-8080.001.patch, YARN-8080.002.patch, YARN-8080.003.patch, YARN-8080.005.patch, YARN-8080.006.patch
>
>
> Existing native service assumes the service is long running and never finishes. Containers will be restarted even if exit code == 0. 
> To support boarder use cases, we need to allow restart policy of component specified by users. Propose to have following policies:
> 1) Always: containers always restarted by framework regardless of container exit status. This is existing/default behavior.
> 2) Never: Do not restart containers in any cases after container finishes: To support job-like workload (for example Tensorflow training job). If a task exit with code == 0, we should not restart the task. This can be used by services which is not restart/recovery-able.
> 3) On-failure: Similar to above, only restart task with exitcode != 0. 
> Behaviors after component *instance* finalize (Succeeded or Failed when restart_policy != ALWAYS): 
> 1) For single component, single instance: complete service.
> 2) For single component, multiple instance: other running instances from the same component won't be affected by the finalized component instance. Service will be terminated once all instances finalized. 
> 3) For multiple components: Service will be terminated once all components finalized.



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