my-docs/kubernetes/workloads/stateful.md

1. Basic Redis StatefulSet

This StatefulSet is configured to run Redis instances in the my-ns namespace with 3 replicas.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: redis
  namespace: my-ns
  labels:
    app.kubernetes.io/name: redis
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: redis
  template:
    metadata:
      labels:
        app.kubernetes.io/name: redis
    spec:
      containers:
      - name: redis
        image: redis

• apiVersion: apps/v1: Specifies the API version.
• kind: StatefulSet: Defines the object as a StatefulSet.
• metadata: Provides metadata for the StatefulSet.
  • name: The name of the StatefulSet (redis).
  • namespace: The namespace where the StatefulSet will be created (my-ns).
  • labels: Key-value pairs to categorize the StatefulSet.
• spec: Describes the desired state.
  • replicas: Number of pod replicas (3).
  • selector: Identifies the pods managed by this StatefulSet.
    • matchLabels: Matches pods with the label app.kubernetes.io/name: redis.
  • template: The pod template used by the StatefulSet.
    • metadata: Metadata for the pod template.
      • labels: Labels applied to the pods (app.kubernetes.io/name: redis).
    • spec: Describes the pod specification.
      • containers: Defines the containers within the pod.
        • name: The name of the container (redis).
        • image: The container image (redis).

2. Redis StatefulSet with Volume

This StatefulSet is similar to the first one but includes persistent volume claims (PVCs) to ensure data persistence.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: redis
  namespace: my-ns
  labels:
    app.kubernetes.io/name: redis
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: redis
  template:
    metadata:
      labels:
        app.kubernetes.io/name: redis
    spec:
      containers:
      - name: redis
        image: redis
        volumeMounts:
          - name: redis-data
            mountPath: /var/lib/redis
  volumeClaimTemplates:
    - metadata:
        name: redis-data
      spec:
        accessModes:
          - "ReadWriteOnce"
        resources:
          requests:
            storage: 1Gi

• apiVersion: apps/v1: Specifies the API version.
• kind: StatefulSet: Defines the object as a StatefulSet.
• metadata: Provides metadata for the StatefulSet.
  • name: The name of the StatefulSet (redis).
  • namespace: The namespace where the StatefulSet will be created (my-ns).
  • labels: Key-value pairs to categorize the StatefulSet.
• spec: Describes the desired state.
  • replicas: Number of pod replicas (3).
  • selector: Identifies the pods managed by this StatefulSet.
    • matchLabels: Matches pods with the label app.kubernetes.io/name: redis.
  • template: The pod template used by the StatefulSet.
    • metadata: Metadata for the pod template.
      • labels: Labels applied to the pods (app.kubernetes.io/name: redis).
    • spec: Describes the pod specification.
      • containers: Defines the containers within the pod.
        • name: The name of the container (redis).
        • image: The container image (redis).
        • volumeMounts: Mounts the specified volume to /var/lib/redis.
          • name: The name of the volume (redis-data).
          • mountPath: The path to mount the volume (/var/lib/redis).
  • volumeClaimTemplates: Defines the PVCs for the StatefulSet.
    • metadata: Metadata for the PVC.
      • name: The name of the PVC (redis-data).
    • spec: Describes the PVC specification.
      • accessModes: Access mode for the PVC (ReadWriteOnce).
      • resources: Resource requests for the PVC.
        • requests: Storage request (1Gi).

3. Web StatefulSet with Volume

This StatefulSet runs NGINX instances with persistent storage.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  selector:
    matchLabels:
      app: nginx # has to match .spec.template.metadata.labels
  serviceName: "nginx"
  replicas: 3 # by default is 1
  minReadySeconds: 10 # by default is 0
  template:
    metadata:
      labels:
        app: nginx # has to match .spec.selector.matchLabels
    spec:
      terminationGracePeriodSeconds: 10
      containers:
      - name: nginx
        image: registry.k8s.io/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: "my-storage-class"
      resources:
        requests:
          storage: 1Gi

• apiVersion: apps/v1: Specifies the API version.
• kind: StatefulSet: Defines the object as a StatefulSet.
• metadata: Provides metadata for the StatefulSet.
  • name: The name of the StatefulSet (web).
• spec: Describes the desired state.
  • selector: Identifies the pods managed by this StatefulSet.
    • matchLabels: Matches pods with the label app: nginx.
  • serviceName: The name of the service that governs this StatefulSet (nginx).
  • replicas: Number of pod replicas (3).
  • minReadySeconds: Minimum time for pods to be ready (10 seconds).
  • template: The pod template used by the StatefulSet.
    • metadata: Metadata for the pod template.
      • labels: Labels applied to the pods (app: nginx).
    • spec: Describes the pod specification.
      • terminationGracePeriodSeconds: Time for the pod to terminate gracefully (10 seconds).
      • containers: Defines the containers within the pod.
        • name: The name of the container (nginx).
        • image: The container image (registry.k8s.io/nginx-slim:0.8).
        • ports: Container ports.
          • containerPort: The container port (80).
          • name: The name of the port (web).
        • volumeMounts: Mounts the specified volume to /usr/share/nginx/html.
          • name: The name of the volume (www).
          • mountPath: The path to mount the volume (/usr/share/nginx/html).
  • volumeClaimTemplates: Defines the PVCs for the StatefulSet.
    • metadata: Metadata for the PVC.
      • name: The name of the PVC (www).
    • spec: Describes the PVC specification.
      • accessModes: Access mode for the PVC (ReadWriteOnce).
      • storageClassName: The storage class name (my-storage-class).
      • resources: Resource requests for the PVC.
        • requests: Storage request (1Gi).