How do you define a network in a version 2 docker-compose definition file?

Question

The documentation about networking is currently very vague on this ― how do you accomplish a docker-compose.yml that creates a virtual network, letting the services (containers) defined by it communicate on that network?

Goal in this scenario being not relying on a pre-defined network, for an ensemble of containers defined for docker-compose. Rather have the network definition self-contained in the docker-compose definition file.

With a pre-defined network, this below would work if the application in A used the name B as the hostname for accessing the application packaged inside B listening on its port 9000. The host:port it would use for it would be B:9000 (more specifically the uri mongodb://B:9000 in my particular case).

foo:
  net: my-pre-defined-network
  container_name: A
  image: foo
bar:
  net: my-pre-defined-network
  container_name: B
  image: bar
  ports:
    - "9000:9000"

But my point is defining a network inside the docker-compose configuration, not assuming one was a-priori defined...

TL;DR

A default network is automatically created. See the beginning section of https://docs.docker.com/compose/networking/ for how to address containers within this network.

Answer 1

Please find below example which include network definition, traffic implementation etc.

version: '2.2'
services: 
  unifiedpushserver: 
    image: docker.io/aerogear/unifiedpush-wildfly:2.1.0 
    networks: 
      - network 
    volumes: 
       - ./helper:/ups-helper:z  
    entrypoint: "/ups-helper/exportKeycloakHost.sh" 
    depends_on: 
       unifiedpushDB: 
         condition: service_healthy 
    environment: <br>
        POSTGRES_SERVICE_HOST: ${POSTGRES_SERVICE_HOST} 
        POSTGRES_USER: ${POSTGRES_USER} 
        POSTGRES_PASSWORD: ${POSTGRES_PASSWORD} 
        POSTGRES_SERVICE_PORT: ${POSTGRES_SERVICE_PORT} 
        POSTGRES_DATABASE: ${POSTGRES_DATABASE} 
        KEYCLOAK_SERVICE_HOST: ${KEYCLOAK_SERVICE_HOST} 
        KEYCLOAK_SERVICE_PORT: ${KEYCLOAK_SERVICE_PORT} 
    labels: 
      traefik.backend: "aerogear" 
      traefik.docker.network: "appliance" 
      traefik.domain: "notification.com" 
      traefik.enable: "true" 
      traefik.frontend.entryPoints: "http, https" 
      traefik.frontend.redirect: "false" 
      traefik.frontend.rule: "Host: notification.com" 
    links: 
      - unifiedpushDB:unifiedpush 
      - keycloakServer:keycloak 
    ports: 
      - 9999:8080 
  unifiedpushDB: 
    image: postgres:9.6 
    networks: 
      - network 
    environment: 
      POSTGRES_USER: ${POSTGRES_USER} 
      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD} 
      POSTGRES_DB: ${POSTGRES_DATABASE} 
    healthcheck: 
      test: ["CMD-SHELL", "pg_isready -U postgres"] 
      timeout: 20s 
      retries: 10 
  keycloakServer: 
    networks: 
      - network 
    image: docker.io/jboss/keycloak:4.1.0.Final 
    command: "-b 0.0.0.0 -Dkeycloak.import=/ups-keycloak-config/ups-realm-sample.json" 
    volumes: 
      - ./keycloak-realm:/ups-keycloak-config:z 
    environment: 
      KEYCLOAK_USER: ${KEYCLOAK_USER} 
      KEYCLOAK_PASSWORD: ${KEYCLOAK_PASSWORD} 
networks: 
     network: 
       external: 
         name: appliance