Kubernetes interview questions

Explain how to deploy a StatefulSet

Let’s try to understand how to install mongodb on k8s using statefulset,

First of all in order to create a replicaset we need the following things,

• a Persistent Volume (PV) with storage class
• a Headless service for network identity

So, we are going to,

• First, we are going to create a headless service using Service deployment using nginx with label app=nginx then we are going to create statefulset for nginx image.
• using volumeClaimTemplate we are going to create persistent volume (PV) with a storage class


---
apiVersion: v1
kind: Service
metadata:
  name: mongo
  labels:
    name: mongo
spec:
  ports:
  - port: 27017
    targetPort: 27017
  clusterIP: None
  selector:
    role: mongo
---
apiVersion: apps/v1beta1
kind: StatefulSet
metadata:
  name: mongo
spec:
  serviceName: "mongo"
  replicas: 3
  template:
    metadata:
      labels:
        role: mongo
        environment: test
    spec:
      terminationGracePeriodSeconds: 10
      containers:
        - name: mongo
          image: mongo
          command:
            - mongod
            - "--replSet"
            - rs0
            - "--smallfiles"
            - "--noprealloc"
          ports:
            - containerPort: 27017
          volumeMounts:
            - name: mongo-persistent-storage
              mountPath: /data/db
        - name: mongo-sidecar
          image: cvallance/mongo-k8s-sidecar
          env:
            - name: MONGO_SIDECAR_POD_LABELS
              value: "role=mongo,environment=test"
  volumeClaimTemplates:
  - metadata:
      name: mongo-persistent-storage
      annotations:
        volume.beta.kubernetes.io/storage-class: "fast"
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 100Gi

Observation

1) We need to observe that we have set the clusterIp to none to create a headless service.

2) Then we created persistent volume with storage class using volumeClaimTemplate