Support pod template for Spark 3.x applications

[ChenYi015]

Purpose of this PR

Close #2101
Close #1690

Proposed changes:

• Add fields spec.driver.template and spec.executor.template to SparkApplication CRD
• Webhook will only mutate Spark pods with label sparkoperator.k8s.io/mutated-by-spark-operator="true", and this label will be added by controller as needed.
• For Spark 2.x applications, the webhook will be used to mutate Spark pods.
• For Spark 3.x applications, the webhook will be used to mutate Spark driver/executor pods only if driver/executor pod template is not defined.
• For all spark applications, the webhook will still be used to mutate Spark pods no matter whether pod template is defined or not.
• Add example spark-pi-pod-template.yaml

Change Category

Indicate the type of change by marking the applicable boxes:

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

Before submitting your PR, please review the following:

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

• The resources section for cpu/memory requests and limits defined in the pod template will not work. Ref: https://spark.apache.org/docs/latest/running-on-kubernetes.html#pod-template.

[ChenYi015]

/hold
/assign @yuchaoran2011 @vara-bonthu @jacobsalway

[yuchaoran2011]

As discussed during the community call, we can think about a future release (maybe 2.1) where we announce the deprecation of web hook and support for Spark 2.x

[jacobsalway]

Would we take the approach of moving to users only being able to specify a pod template, or map the existing struct fields and construct a pod template on the fly during submission?

[ImpSy]

I feel like mapping existing field to a pod template on the fly + new parameter templateFile go be the easiest migration path for existing user

[Tom-Newton]

For now I would personally find it useful to support webhook mutations and template on the same SparkApplication.

[yuchaoran2011]

/lgtm

[vara-bonthu]

@ChenYi015 Thanks for adding this much needed feature! PR looks good to me. You may need to resolve the conflicts to move forward.

[ChenYi015]

@vara-bonthu Thanks for the review. I have resolved the merge conflicts.

[ChenYi015]

/unhold

[vara-bonthu]

/approve

[ImpSy]

I know that the PR has been approved but I feel like introducing a new key is not the right implementation here

We should either build the template with the current CR if spark version >= 3 or have the possibility to specify a template file name to use

This implementation force a migration for our user if they want to get rid of webhook but it should be free for them (which is not the case here)

[ChenYi015]

I know that the PR has been approved but I feel like introducing a new key is not the right implementation here

We should either build the template with the current CR if spark version >= 3 or have the possibility to specify a template file name to use

This implementation force a migration for our user if they want to get rid of webhook but it should be free for them (which is not the case here)

@ImpSy

1. It is somewhat difficult to build a template file form current CRD, it would be more easy and straight to use the template defined in spec.[driver|executor].template
2. If one want to specify a pod template file, he can use the spark conf spark.kubernetes.[driver|executor].podTemplateFile.
3. Maybe we should make webhook and pod template both work in this PR so that users can have time to migrate their applications to use pod templates.

[Tom-Newton]

My user perspective is that I like introducing the new template fields now to enable new functionality but I'm not ready yet, to fully migrate away from the webhook, so I currently would like to use both.

Before the webhook is deprecated though I think the template should be built from the current CR as ImpSy suggests.

[ChenYi015]

I have updated this PR, the webhook will still be used to mutate Spark pods no matter pod template is defined or not. I will try to build the pod template file from the current CRD when we try to deprecate the webhook.

[Tom-Newton]

LGTM, though my review probably doesn't mean much 🙂

[vara-bonthu]

/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Tom-Newton, vara-bonthu, yuchaoran2011

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