[jira] [Commented] (SPARK-25262) Make Spark local dir volumes configurable with Spark on Kubernetes

["Junjie Chen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-25262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16817499#comment-16817499 ] 

Junjie Chen commented on SPARK-25262:
-------------------------------------

Hi 

Do we have plan to for second change mentioned above for checking existing volume logic?   

> Make Spark local dir volumes configurable with Spark on Kubernetes
> ------------------------------------------------------------------
>
>                 Key: SPARK-25262
>                 URL: https://issues.apache.org/jira/browse/SPARK-25262
>             Project: Spark
>          Issue Type: Improvement
>          Components: Kubernetes
>    Affects Versions: 2.3.0, 2.3.1
>            Reporter: Rob Vesse
>            Priority: Major
>
> As discussed during review of the design document for SPARK-24434 while providing pod templates will provide more in-depth customisation for Spark on Kubernetes there are some things that cannot be modified because Spark code generates pod specs in very specific ways.
> The particular issue identified relates to handling on {{spark.local.dirs}} which is done by {{LocalDirsFeatureStep.scala}}.  For each directory specified, or a single default if no explicit specification, it creates a Kubernetes {{emptyDir}} volume.  As noted in the Kubernetes documentation this will be backed by the node storage (https://kubernetes.io/docs/concepts/storage/volumes/#emptydir).  In some compute environments this may be extremely undesirable.  For example with diskless compute resources the node storage will likely be a non-performant remote mounted disk, often with limited capacity.  For such environments it would likely be better to set {{medium: Memory}} on the volume per the K8S documentation to use a {{tmpfs}} volume instead.
> Another closely related issue is that users might want to use a different volume type to back the local directories and there is no possibility to do that.
> Pod templates will not really solve either of these issues because Spark is always going to attempt to generate a new volume for each local directory and always going to set these as {{emptyDir}}.
> Therefore the proposal is to make two changes to {{LocalDirsFeatureStep}}:
> * Provide a new config setting to enable using {{tmpfs}} backed {{emptyDir}} volumes
> * Modify the logic to check if there is a volume already defined with the name and if so skip generating a volume definition for it



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