KEP-5307 Initial KEP for container restart policy #5308

yuanwang04 · 2025-05-16T22:17:33Z

One-line PR description: Initial KEP for container restart policy

Issue link: Container restart rules to customize the pod restart policy #5307

Other comments: Discussion link https://docs.google.com/document/d/13fQu343OBEM2ICHLXfWHrApmzskd4nY3xWI27EbMJyI/edit?tab=t.0

k8s-ci-robot · 2025-05-16T22:17:42Z

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k8s-ci-robot · 2025-05-16T22:17:44Z

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SergeyKanzhelev · 2025-05-16T22:25:48Z

keps/sig-node/5307-container-restart-policy/README.md

+we may need to implement as described here: https://github.com/kubernetes/enhancements/issues/3329#issuecomment-1571643421
+
+```
+restartPolicy: Never


@dchen1107 I remember you had a concern with having Never pod with the container inside it that has restart count increasing. How strong is this concern? Strong enough to iontroduce the restartPolicy: Custom?

k8s-ci-robot · 2025-05-16T22:26:05Z

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kannon92 · 2025-05-18T14:13:40Z

/ok-to-test

kannon92 · 2025-05-20T18:54:22Z

keps/sig-node/5307-container-restart-policy/README.md

+- name: myapp1
+  # the default behavior is inherited from the Pod’s restartPolicy
+  restartPolicy: Custom 
+  # pod-level API for specifying container restart rules


This API is at the container level it seems.

Yes, just mentioning it here since there are some discussion around whether we need to introduce another pod-level restart policy #5308 (comment)

A big concern is once we introduced pod-level restart policy, how to interact with job failure policy? Maybe not today.

kannon92 · 2025-05-20T18:55:37Z

keps/sig-node/5307-container-restart-policy/README.md

+The container restart will still follow the exponential backoff to avoid
+excessive resource consumption due to restarts.
+
+## Design Details


How does this interact with PodFailurePolicy?

Added discussion around Job's PodFailurePolicy. Basically, this shouldn't affect how Job handles pod failures. Job only checks container exit codes (for PodFailurePolicy) when the Pod finished (and restartPolicy=Never). However, if the container is restarted by the proposed container restart policy, the pod will still be Running, and Job controller will not kick in.

keps/sig-node/5307-container-restart-policy/README.md

mimowo · 2025-05-28T17:01:46Z

keps/sig-node/5307-container-restart-policy/README.md

+containers:
+- name: myapp1
+  # the default behavior is inherited from the Pod’s restartPolicy
+  restartPolicy: Custom 


I would suggest to consider alternative names, maybe:

"RuleBased"

"Conditional"

I'm leaning to "RuleBased" to match the "restartRules" name.

mimowo · 2025-05-28T17:03:55Z

keps/sig-node/5307-container-restart-policy/README.md

+  # the default behavior is inherited from the Pod’s restartPolicy
+  restartPolicy: Custom 
+  # pod-level API for specifying container restart rules
+  restartRules: 


I would suggest to propose the full API, similarly as here, and provide this yaml as an example.

mimowo · 2025-05-28T17:06:42Z

keps/sig-node/5307-container-restart-policy/README.md

+know that this has succeeded?
+-->
+
+- Allow the Pod with the restartPolicy=Custom to keep restarting a container


Suggested change

- Allow the Pod with the restartPolicy=Custom to keep restarting a container

- Introduce API which allows to keep restarting a container

I guess at this point we don't need to provide the shape of the API

mimowo · 2025-05-28T17:11:12Z

keps/sig-node/5307-container-restart-policy/README.md

+
+#### Story 1
+
+The Pod with two containers - one is the main container and one is the sidecar


I would suggest to orient the "Story" from the perspective of the Kubernetes users. For example, as an ML researcher I'm creating long-running AI/ML workloads. Pods in such workloads are unavoidable due to various reasons, but in many cases they are recoverable. I would like to be able to avoid re-scheduling the workload as this consumes signifficant amount of time, and only restart the failed container "in-place".

Feel free to rephrase as you see fit.

mimowo · 2025-05-28T17:13:51Z

keps/sig-node/5307-container-restart-policy/README.md

+may have containers restarted and have the restart count higher than 0. This may
+also affect how Job `podFailurePolicy` interacts with pod failures.


Actually, I think this approach is fully transparent to the Job controller, because the Job controller only matches Pods in terminal phase. It is mentioned here:

enhancements/keps/sig-apps/3329-retriable-and-non-retriable-failures/README.md

Lines 902 to 903 in fc234c1

When matching a failed pod against Job pod failure policy, it is important that

the pod is actually in the terminal phase (`Failed`), to ensure their state is

mimowo · 2025-05-28T17:29:21Z

keps/sig-node/5307-container-restart-policy/README.md

+This works with Job `podFailurePolicy` without any changes on Job API. Currently,
+Job only checks for `podFailurePolicy` after the Pod has finished running.
+Kubelet restarting the container of the Pod will not change the Pod's status.
+This is the ideal improvement where the Job configured `podFailurePolicy`


I suggest to avoid phrases like " ideal improvement", let's leave it to reviewers :)

mimowo · 2025-05-28T17:34:43Z

keps/sig-node/5307-container-restart-policy/README.md

+The proposal is to implement a simple API with the very limited set of
+allowed values to [Container](https://github.com/kubernetes/kubernetes/blob/master/pkg/apis/core/types.go#L2528)
+under k8s.io/apis/core. The shape of API is informed by some future improvements


Suggested change

The proposal is to implement a simple API with the very limited set of

allowed values to [Container](https://github.com/kubernetes/kubernetes/blob/master/pkg/apis/core/types.go#L2528)

under k8s.io/apis/core. The shape of API is informed by some future improvements

The proposal is to extend the Pod's [container API](https://github.com/kubernetes/kubernetes/blob/master/pkg/apis/core/types.go#L2528) to allow to restarting containers based on

the container's end state, e.g. exit code.

I would suggest to avoid using adjective like "simple API", or "very limited set". Let's leave it to the readers / reviewers to assess.

mimowo · 2025-05-28T17:37:48Z

keps/sig-node/5307-container-restart-policy/README.md

+we may need to implement as described here:
+https://github.com/kubernetes/enhancements/issues/3329#issuecomment-1571643421


Actually, this reference is slightly different that the current proposal. One difference is that the reference assumes "OnFailure". Instead of design details I would propose to move it to the Notes and Caveats section.

mimowo · 2025-05-28T17:38:20Z

keps/sig-node/5307-container-restart-policy/kep.yaml

+# The following PRR answers are required at alpha release
+# List the feature gate name and the components for which it must be enabled
+feature-gates:
+  - name: MyFeature


ContainerRestartPolicy ?

mimowo · 2025-05-28T17:38:50Z

keps/sig-node/5307-container-restart-policy/kep.yaml

+
+# The following PRR answers are required at beta release
+metrics:
+  - my_feature_metric


Cleanup. This is alpha, so IIUC no need for metric yet.

mimowo · 2025-05-28T17:39:32Z

@yuanwang04 thank you for the work, I like this proposal, AFAIK this approach is fully compatible with the Job's podFailurePolicy (at least if I'm not missing something), because when Pod's restartPolicy: Never, then Job's podFailurePolicy only analyzes pods which reach the "Failed" phase. Here, the pods avoid reaching the failed phase. Once they reach, they will be matched against podFailurePolicy which may decide to recreate the entire pod.

k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label May 16, 2025

k8s-ci-robot requested review from dchen1107 and derekwaynecarr May 16, 2025 22:17

k8s-ci-robot added kind/kep Categorizes KEP tracking issues and PRs modifying the KEP directory sig/node Categorizes an issue or PR as relevant to SIG Node. labels May 16, 2025

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SergeyKanzhelev reviewed May 16, 2025

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yuanwang04 force-pushed the container-restart-policy branch from 6cb2b80 to 0cbfc18 Compare May 16, 2025 22:25

k8s-ci-robot added ok-to-test Indicates a non-member PR verified by an org member that is safe to test. and removed needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels May 18, 2025

yuanwang04 force-pushed the container-restart-policy branch from 0cbfc18 to 040ffef Compare May 19, 2025 21:45

kannon92 reviewed May 20, 2025

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yuanwang04 force-pushed the container-restart-policy branch 4 times, most recently from dd2b1f7 to bee6cce Compare May 23, 2025 01:26

KEP-5307 Initial KEP for container restart policy

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yuanwang04 force-pushed the container-restart-policy branch from bee6cce to 67df630 Compare May 23, 2025 01:36

mimowo reviewed May 28, 2025

View reviewed changes

	- Allow the Pod with the restartPolicy=Custom to keep restarting a container
	- Introduce API which allows to keep restarting a container


		#### Story 1

		The Pod with two containers - one is the main container and one is the sidecar

		may have containers restarted and have the restart count higher than 0. This may
		also affect how Job `podFailurePolicy` interacts with pod failures.

	When matching a failed pod against Job pod failure policy, it is important that
	the pod is actually in the terminal phase (`Failed`), to ensure their state is

		we may need to implement as described here:
		https://github.com/kubernetes/enhancements/issues/3329#issuecomment-1571643421

KEP-5307 Initial KEP for container restart policy #5308

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KEP-5307 Initial KEP for container restart policy #5308

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