2.2.2 Continuing to work with the Configuration File

  1. Next let’s expose the port that the user needs to access the postgres application. And if you look at the image on DockerHub you will see that a number of environment variables need to be defined.

    apiVersion: apps/v1
kind: Deployment
metadata:
  name: db
  labels:
    service: db
spec:
  selector:
    matchLabels:
      service: db
  template:
    metadata:
      labels:
        service: db
    spec:
      containers:
      - image: postgres:11-alpine
        name: postgres
        ports:
          - containerPort: 5432
        env:
        - name: POSTGRES_PASSWORD
          value: "password"
        - name: POSTGRES_USER
          value: "user"  
        - name: PGDATA
          value: "/var/lib/postgresql/data/mydata"

  2. The postgres database also needs a folder to write it’s data to. So we need to add spec.containers.volumeMounts and spec.volumes:

    apiVersion: apps/v1
kind: Deployment
metadata:
  name: db
  labels:
    service: db
spec:
  selector:
    matchLabels:
      service: db
  template:
    metadata:
      labels:
        service: db
    spec:
      containers:
      - image: postgres:11-alpine
        name: postgres
        ports:
          - containerPort: 5432
        env:
        - name: POSTGRES_PASSWORD
          value: "password"
        - name: POSTGRES_USER
          value: "user"  
        - name: PGDATA
          value: "/var/lib/postgresql/data/mydata"
        volumeMounts:
        - mountPath: /var/lib/postgresql/data
          name: postgresdb 
      volumes:
      - name: postgresdb

  3. This configuration is pretty close to complete. But as is, it’s hard to access the postgres service. To make it easier, we need to create a Service so that other pods can access this one using the name db. A Service adds on to the Deployment, so it doesn’t contain any containers. It does however need to specify ports and selectors:

    apiVersion: v1
kind: Service
metadata:
  labels:
    service: db 
  name: db
spec:
  ports:
  - port: 5432
    protocol: TCP
    targetPort: 5432
  selector:
    service: db

  4. You can have multiple configurations in a single file as long as they are separated by a line with three dashes.