StatefulSet ¶

Scenario:

• Create Headless Service nginx and StatefulSet web
• Scale out StatefulSet web

Demo:

Create Headless Service nginx and StatefulSet web.

kubectl apply -f - << EOF
---
apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
          name: web
EOF

Get details of StatefulSet Pod created just now.

kubectl get pod | grep web

Result

NAME    READY   STATUS    RESTARTS   AGE
web-0   1/1     Running   0          27s
web-1   1/1     Running   0          10s

Use command kubectl edit sts web to update an existing StatefulSet. ONLY these fields can be updated: replicas、image、rolling updates、labels、resource request/limit and annotations.

Note: When StatefulSet Pod is dead in current node, no copies will be created in other node automatically.

Scale out StatefulSet.

Scale StatefulSet web to 5 Replicas.

kubectl scale sts web --replicas=5

Info

• Partition indicates the ordinal at which the StatefulSet should be partitioned for updates. During a rolling update, all pods from ordinal Replicas-1 to Partition are updated. All pods from ordinal Partition-1 to 0 remain untouched.
• This is helpful in being able to do a canary based deployment.
• The default value is 0.
• Command: kubectl explain statefulsets.spec.updateStrategy.rollingUpdate.partition

Clean up.

kubectl delete sts web
kubectl delete service nginx