Add support for pods to differentiate between a scale down and a shutdown events

[mattrpav]

Enhancement Description

• Support an optional lifecycle hook for signaling scale down
  or
• Support a flag or argument to existing PreStop lifecycle hook to indicate scale down

Background

Currently, there is not a way for a workload running in pod to differentiate between a scale down and a shutdown. Pod shutdown down scenarios are common for upgrades, Kuberentes patching, or moving the pod to a different node for Node patching.

Maintenance windows would be lower for stateful workloads if they were able to differentiate between scale down and shutdown in order to only handle draining or transferring of data during scale down, instead of having to drain for every shutdown scenario.

/sig apps

[mattrpav]

/sig apps

[kikisdeliveryservice]

@mattrpav Issues in this repo are for opening and tracking KEPs. As the issue template and README indicate, you should be talking directly to the SIG with your idea before opening an issue in this repo:

Discussion Link: link to SIG mailing list thread, meeting, or recording where the Enhancement was discussed before KEP creation

Please contact sig-apps with your idea: https://github.com/kubernetes/community/tree/master/sig-apps

If they direct you to open a KEP, please open an issue in this repo and fill out the issue template (making sure to fill in the discussion link section) before opening your KEP PR.

[kannon92]

/transfer kubernetes

[k8s-ci-robot]

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[kannon92]

cc @atiratree @rthallisey

Curious what you all think from wg-node-lifecycle?

[kannon92]

/reopen