Stateful Set

tip

The StatefulSet manifest structure is almost identical to Deployment manifest.

• StatefulSet Pods are not anonymous, they have unique identities & unique PVCs.
• Pods are created sequentially, in an order, with sequential pod names
• They get their own PVCs automatically.
• PVCs created by StatefulSets are not deleted automatically on scale-down, only on StatefulSet deletion (if cascade=true).
• • If the StatefulSet scales back up, it will reuse the exact same PVCs
• Pods running database servers are great fit

Cmds

kubectl get statefulsets # sts
kubectl get pods --field-selector metadata.ownerReferences[0].kind=StatefulSet # filter by owner

How to find them

$ kubectl get sts
# e.g.
NAME   READY   AGE
web    3/3     10m

$ kubectl get pods -l app=web

StatefulSet Manifest

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "web"
  replicas: 3  # Initial value, HPA will modify
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: nginx
        image: nginx
        resources:
          requests:
            cpu: "100m"
          limits:
            cpu: "500m"
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates: # only for StatefulSets, not for Deployments
  - metadata:
      name: www
    spec:
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 1Gi
      storageClassName: standard

Autoscale Stateful Sets

kubectl autoscale statefulset my-stateful-app --cpu-percent=75 --min=3 --max=10

StatefulSet Autoscaler Manifest

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: web-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: StatefulSet
    name: web
  minReplicas: 3
  maxReplicas: 10
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 75