Pod Anti Affinity

Create a nginx deployment with 3 pods

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: gcr.io/google_containers/nginx-slim:0.9
        ports:
        - containerPort: 8080

Add a ‘podAntiAffinity’ section to the deployment

The goal is to distribute all pod for this deployment across different nodes.

Use the affinity of this example to write the affinity section in the deployment.yaml file:

apiVersion: v1
kind: Pod
metadata:
  name: with-pod-antiaffinity
spec:
  affinity:
    podAntiAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchExpressions:
          - key: security
            operator: In
            values:
            - S1
        topologyKey: topology.kubernetes.io/zone
  containers:
  - name: with-pod-affinity
    image: registry.k8s.io/pause:2.0
Note

The topologyKey value will be kubernetes.io/hostname because pod will not be on the same nodes.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - nginx
            topologyKey: kubernetes.io/hostname
      containers:
      - name: nginx
        image: gcr.io/google_containers/nginx-slim:0.9
        ports:
        - containerPort: 8080

  • Check that all pods are running on different nodes using: kubectl get pods -o wide

  • Scale the Deployment to five pods and try to understand what’s happening.