apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-sentinel
  namespace: redis
  labels:
    app: redis-sentinel
spec:
  replicas: 3
  selector:
    matchLabels:
      app: redis-sentinel
  template:
    metadata:
      labels:
        app: redis-sentinel
    spec:
      # Init container to copy the sentinel.conf from the ConfigMap to a writable emptyDir volume.
      initContainers:
      - name: copy-sentinel-config
        image: busybox
        command: ['sh', '-c', 'cp /config/sentinel.conf /writable/']
        volumeMounts:
        - name: sentinel-config-readonly
          mountPath: /config
        - name: sentinel-config
          mountPath: /writable
      containers:
      - name: redis-sentinel
        image: redis:7.4-alpine
        ports:
        - containerPort: 26379
          name: sentinel
        command:
          - "redis-sentinel"
          - "/etc/redis/sentinel.conf"
        volumeMounts:
        - name: sentinel-config
          mountPath: /etc/redis  # this volume is now writable
      volumes:
      # Mount the ConfigMap as a read-only volume for the init container
      - name: sentinel-config-readonly
        configMap:
          name: redis-sentinel-config
      # EmptyDir volume to hold the writable config file
      - name: sentinel-config
        emptyDir: {}