version: '3'
services:
  datastore:
    image: busybox
    volumes:
      - db_data:/var/lib/psql
  postgresql:
    image: postgres
    environment:
      POSTGRES_USER: username
      POSTGRES_PASSWORD: password
    ports:
      - "5432:5432"
    volumes:
      - db_data:/var/lib/psql
volumes:
  db_data: