CODEWITHSUNDEEP
kubernetes
janosi
janosi

Reputation: 89

Graceful shutdown of explicitly selected pod

I would like to remove a given, exact, selected pod from a set of pods controlled by the same Replication Controller, or the same Replica Set.
The use case is the following: each pod in the set runs a stateful (but in-memory) application. I would like to remove a pod from the set on a graceful way, i.e. before the removal I would like to be sure, that there are no ongoing application sessions handled by the pod. Let's say I can solve the task of emptying the pod on application level, i.e. no new sessions are directed to the selected pod, and I can measure the number of ongoing sessions in the pod, so I can decide when to remove the pod. The hard part is to remove this pod so, that RC or RS does not replace the pod with a new one based on the value of "replicas".
I could not find a solution for this. The nearest one would be to isolate the pod from the RC or RS as suggested by http://kubernetes.io/docs/user-guide/replication-controller/#isolating-pods-from-a-replication-controller Though, the RC or RS replaces the isolated pod with a new one, according to the same document. And I as can understand there is no way to isolate the pod and decrease the value of "replicas" on an atomic way.
I have checked the coming PetSet support, but my application does not require e.g. persistent storage, or persistent pod ID. Such features are not necessary in my case, so my application is not really a pet from this perspective.
Maybe a new pod state (e.g. "target for removal" - state name is not important for me) would make it, which could be patched via the API, and which would be considered by RC or RS when the value of "replicas" is decreased?

Upvotes: 0

Views: 233

Answers (1)

caesarxuchao
caesarxuchao

Reputation: 1109

You can achieve this in three steps:

  1. Add a label to all pods except the one you want to delete. Because the labels of the pods still satisfy the selector of the Replica Set, so no new pods will be created.

  2. Update the Replica Set: adding the new label to the selector and decrease the replicas of the Replica Set atomically. The pod you want to deleted won't be selected by the Replica Set because it doesn't have the new label.

  3. Delete the selected pod.

Upvotes: 1

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