I use docker-compose v1.6.0 and docker engine 1.10.0.

I have the following docker-compose.yml:

version: '2'

services:
  db:
    image: postgres
    environment:
      POSTGRES_DB: test
      POSTGRES_USER: test
      POSTGRES_PASSWORD: test1234
    volumes:
      - db-data:/var/lib/postgresql/data
  web:
    build: .
    command: /bin/bash -c "bundle exec rake db:migrate && bundle exec rails s -p 3000 -b 0.0.0.0"
    environment:
      RAILS_ENV: production
      DB_HOST: db
      DB_PORT: 5432
      DB_USER: test
      DB_DB: test
      DB_PASSWORD: test1234
      SECRET_KEY_BASE: 5ffbf99dcae1dee8500abd759114f473a942cb23a23db2ef8ce61972d2eaeedbb656ddb184ff0175ab4f8c5bcb29fa860505a140a6442608192dee1e3b168928
    ports:
      - "3000:3000"
    volumes:
      - public:/myapp/public
volumes:
  db-data:
    driver: local
  public:
    driver: local

But while starting containers with docker-compose up command, I see following error: web_1 | PG::ConnectionBad: could not translate host name "db" to address: Name or service not known.

I tried to find the reasons for this error:

[user@localhost test_project]$ docker-compose run web bash
Starting test_project_db_1
root@9bd26d6496bd:/myapp# cat /etc/hosts
127.0.0.1   localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.18.0.3  9bd26d6496bd
root@9bd26d6496bd:/myapp# ping db
ping: unknown host

I added the following to web section in the docker-compose, but this has no effect:

    links:
      - db:db
    depends_on:
      - db