StatefulSet

Info

Stateless application does not create dependencies on the local system, while stateful does.

Create new stateful set

---
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:latest
        ports:
        - containerPort: 80
          name: web

kubectl create -f web.yaml

Check the stateful set

kubectl get sts
kubectl get po

Testing if two web services are working

statefulSet-test.png

Scaling up and down

kubectl scale sts web --replicas=5

Maintain the sequence of scaling up and down

Canary Release

Minimizing issues and impacts after a project goes live involves careful planning, monitoring, and quick response strategies.

Use edit to change the configuration of the stateful set, and modify the partition in YAML.

e.g. if partition: 1, all 5 web pods will be updated except web-0.

On Delete

Change updateStrategy: type: OnDelete

Only update if the deletion is made. A new pod will be generated immediately after the deletion.