Support PodRequests calculations for initContainers with restartPolicy: Always

[jonathan-innis]

Description

What problem are you trying to solve?

Kubernetes 1.28 introduces the SidecarContainers feature into alpha. This feature means that sidecar containers can now be ordered, meaning that upstream K8s have essentially collapsed the concept of a sidecar container down into an ordered init container with a restartPolicy set to Always. This change means that we now have to consider initContainers in our calculation of pod resource requests differently if they have a restartPolicy set to Always (since this means that the resource requests will always be utilized for all containers on the pod to run).

The changes the calculation from:

podRequests = max(max(each initContainers[i]),sum(containers))

to:

initContainerRequests[i] = sum(sidecar containers with index < i) + initContainers[i]
podRequests = max(max(each initContainers[i]) , sum(sidecarContainers) + sum(containers))

Relevant Links

Upstream Resource Request Calculation Code: https://github.com/kubernetes/kubernetes/blob/e2afa175e4077d767745246662170acd86affeaf/pkg/api/v1/resource/helpers.go#L96
KEP: https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/753-sidecar-containers/README.md
Blog: https://www.mirantis.com/blog/understanding-kubernetes-new-sidecar-container-feature

How important is this feature to you?

This is a supported feature in upstream that is currently in Alpha but has sufficient momentum that there is belief in the community that it will be quickly pushed to Beta, where Karpenter will want to support it.

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[sadath-12]

Happy to help with this issue . Assign me