docker-compose：为什么代理和应用程序服务因主机名而失败？

以下是 v2 规范中工作的 docker-compose 文件：

version: '2'

volumes:
  webroot:
    driver: local


services:
  app: # Launch uwsgi application server
    build:
      context: ../../
      dockerfile: docker/release/Dockerfile
    links:
      - dbc
    volumes:
      - webroot:/var/www/someapp
    environment:
      DJANGO_SETTINGS_MODULE: someapp.settings.release
      MYSQL_HOST: dbc
      MYSQL_USER: todo
      MYSQL_PASSWORD: passwd
    command:
      - uwsgi
      - "--socket /var/www/someapp/someapp.sock"
      - "--chmod-socket=666"
      - "--module someapp.wsgi"
      - "--master"
      - "--die-on-term"

  test: # Run acceptance test cases
    image: shamdockerhub/someapp-specs
    links:
      - nginx
    environment:
      URL: http://nginx:8000/todos
      JUNIT_REPORT_PATH: /reports/acceptance.xml
      JUNIT_REPORT_STACK: 1
    command: --reporter mocha-jenkins-reporter

  nginx: # Start nginx web server that forwards https packets to uwsgi server
    build:
      context: .
      dockerfile: Dockerfile.nginx
    ports:
      - "8000:8000"
    links:
      - app
    volumes:
      - webroot:/var/www/someapp

  dbc: # Launch MySQL server
    image: mysql:5.6
    hostname: dbr
    expose:
      - "3306"
    environment:
      MYSQL_DATABASE: someapp
      MYSQL_USER: todo
      MYSQL_PASSWORD: passwd
      MYSQL_ROOT_PASSWORD: passwd

  agent: # Ensure DB server is runnin
    image: shamdockerhub/ansible
    links:
      - dbc
    environment:
      PROBE_HOST: "dbc"
      PROBE_PORT: "3306"
    command: ["probe.yml"]

其中条目

  MYSQL_HOST: dbc

  PROBE_HOST: "dbc"

看起来不直观，因为hostname被设定为dbr in dbc service

1)

app使用时服务失败并出现以下错误MYSQL_HOST: dbr

   django.db.utils.OperationalError: (2005, "Unknown MySQL server host 'dbr' (0)")

2)

agent当下面的 ansible 代码中时，服务也会失败PROBE_HOST: "dbr"

set_fact:
      probe_host: "{{ lookup('env', 'PROBE_HOST') }}"
local_action: >
      wait_for host={{ probe_host }}

1)

为什么这两项服务的价值却失败了dbr?

2)

如何使这两个服务协同工作MYSQL_HOST: dbr and PROBE_HOST: "dbr"?

这就是 Docker 的工作原理，因为hostname不是唯一的，如果您为两个容器提供相同的主机名，则会导致问题，因此 compose 将始终使用服务名称进行 DNS 解析