Kubernetes pod in more replicas - anti affinity rule

Question

I have a question about K8S pod anti affinity rule. What I have and what I need.

I have cross 2 data centers K8S cluster. In every DC is for example 5 nodes. I have a Deployment for Pod, which runs in 10 replicas cross all 10 nodes. For every node is 1 Pod replica. And I want to set up rule for case, if one DC will crash, to not migrate 5 replicas from crashed DC to health DC.

I found, that it could be possible to do it throught "Anti-affinity" rule, but I can't find any example for this scenario. Do you have example for it?

Hi, yea you need to use kubernetes.io/docs/concepts/configuration/assign-pod-node/… and this example has the podAntiAffinity stanza kubernetes.io/docs/tutorials/stateful-application/zookeeper/… — Suresh Vishnoi

wolmi wolmi · Accepted Answer · 2019-07-09T09:48:15

From the documentation https://kubernetes.io/docs/concepts/configuration/assign-pod-node/

you need to set a selector on your deployment and indicate in the anti-affinity section what is the value to match and make the anti-affinity true:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-cache
spec:
  selector:
    matchLabels:
      app: store
  replicas: 3
  template:
    metadata:
      labels:
        app: store
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - store
            topologyKey: "kubernetes.io/hostname"
      containers:
      - name: redis-server
        image: redis:3.2-alpine

You can see that it is using a label selector that try to find the key app with value store it means that if a node has already a pod with that label and value kubernetes will apply anti-affinity.

Kubernetes pod in more replicas - anti affinity rule

2 Answers