K8S pods with two replicas on different nodes

Question

I've pods with two replicas, does it make sense that k8s will reschedule both replicas in the same time ? if yes is there a way to avoid it?

I guess(according to the replies from @Henry) that I need to use https://kube.netes.io/docs/concepts/scheduling-eviction/assign-pod-node/#affinity-and-anti-affinity or

topology https://kube.netes.io/blog/2020/05/introducing-podtopologyspread/

But not sure how to configure following:

1 application with 2 replicas that for example

Replica A runs on nodeFoo and

Replica B run in NodeBar

Answer 1

To configure the replicas to run on different nodes podAntiAffinity can be used. For example in the deployment spec:

spec:    
  template:
    metadata:
      labels:
        name: my-app-label
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            - labelSelector:
                matchLabels:
                  name: my-app-label
              topologyKey: kubernetes.io/hostname

This basically means, all pods matched by the label name=my-app-label should run on hosts where the node label kube.netes.io/hostname is different.

Answer 2

Assuming you mean a Deployment, yes the Pod objects are created and scheduled roughly simultaneously. If you want things to be created in order, use a StatefulSet.