docker-compose with env variables

version: '3'

services:
  app:
    build: ./src
    container_name: sskey_app
    links:
     - db
    environment:
     - POSTGRES_USER=postgres
      - POSTGRES_PASS=postgres
      - POSTGRES_HOST=db  # database service name
      - POSTGRES_NAME=db_sskey
    ports:
     - "5000:5000"
    depends_on:
     - db

  db:
    image: postgres:10.4
    container_name: sskey_db
    restart: always
    environment:
     - POSTGRES_USER=postgres
      - POSTGRES_PASS=postgres
      - POSTGRES_HOST=db  # database service name
      - POSTGRES_NAME=db_sskey
    ports:
     - "5432:5432"