Stateful Sets in Kubernetes

Stateful Sets are a Kubernetes resource used to manage stateful applications. They provide guarantees about the ordering and uniqueness of pods, making them suitable for applications that require stable network identities and persistent storage.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-statefulset
spec:
  serviceName: "my-service"  # Service that manages the network identity of the pods
  replicas: 3  # Number of replicas
  selector:
    matchLabels:
      app: myapp  # Label selector to identify the pods managed by this StatefulSet
  template:
    metadata:
      labels:
        app: myapp  # Labels for the pods
    spec:
      containers:
      - name: mycontainer
        image: myimage  # Container image
        ports:
        - containerPort: 80  # Port exposed by the container
        volumeMounts:
        - name: myvolume  # Name of the volume to mount
          mountPath: /data  # Path inside the container where the volume will be mounted
  volumeClaimTemplates:  # Template for creating Persistent Volume Claims
  - metadata:
      name: myvolume
    spec:
      accessModes:
      - ReadWriteOnce  # The volume can be mounted as read-write by a single node
      resources:
        requests:
          storage: 1Gi  # Size of the persistent volume
      storageClassName: my-storage-class  # Storage class to use for the persistent volume

Key Features of Stateful Sets

Stable Network Identity: Each pod in a Stateful Set has a unique, stable network identity, which is maintained across rescheduling.
Ordered Deployment and Scaling: Pods are created, updated, and deleted in a defined order, ensuring that the application can handle changes gracefully.
Persistent Storage: Stateful Sets can automatically provision persistent storage for each pod using Persistent Volume Claims, ensuring that data is retained even if the pod is rescheduled or restarted.
Rolling Updates: Stateful Sets support rolling updates, allowing you to update the application without downtime.