Docker Networking - nginx: [emerg] host not found in upstream

There is a possibility to use "volumes_from" as a workaround until depends_on feature (discussed below) is introduced. All you have to do is change your docker-compose file as below:

nginx:
  image: nginx
  ports:
    - "42080:80"
  volumes:
    - ./config/docker/nginx/default.conf:/etc/nginx/conf.d/default.conf:ro
  volumes_from:
    - php

php:
  build: config/docker/php
  ports:
    - "42022:22"
  volumes:
    - .:/var/www/html
  env_file: config/docker/php/.env.development

mongo:
  image: mongo
  ports:
    - "42017:27017"
  volumes:
    - /var/mongodata/wa-api:/data/db
  command: --smallfiles

One big caveat in the above approach is that the volumes of php are exposed to nginx, which is not desired. But at the moment this is one docker specific workaround that could be used.

depends_on feature This probably would be a futuristic answer. Because the functionality is not yet implemented in Docker (as of 1.9)

There is a proposal to introduce "depends_on" in the new networking feature introduced by Docker. But there is a long running debate about the same @ https://github.com/docker/compose/issues/374 Hence, once it is implemented, the feature depends_on could be used to order the container start-up, but at the moment, you would have to resort to one of the following:

1. make nginx retry until the php server is up - I would prefer this one
2. use volums_from workaround as described above - I would avoid using this, because of the volume leakage into unnecessary containers.

This can be solved with the mentioned depends_on directive since it's implemented now (2016):

version: '2'
  services:
    nginx:
      image: nginx
      ports:
        - "42080:80"
      volumes:
        - ./config/docker/nginx/default.conf:/etc/nginx/conf.d/default.conf:ro
      depends_on:
        - php

    php:
      build: config/docker/php
      ports:
        - "42022:22"
      volumes:
        - .:/var/www/html
      env_file: config/docker/php/.env.development
      depends_on:
        - mongo

    mongo:
      image: mongo
      ports:
        - "42017:27017"
      volumes:
        - /var/mongodata/wa-api:/data/db
      command: --smallfiles

Successfully tested with:

$ docker-compose version
docker-compose version 1.8.0, build f3628c7

Find more details in the documentation.

There is also a very interesting article dedicated to this topic: Controlling startup order in Compose