Gitlab runner docker Could not resolve host

Question

Im using 2 containers on my Ubuntu OS: Gitlab-ce and gitlab-runner

Containers names are: gitlab_gitlab_1 and gitlab_gitlab-runner_1

I access to my gitlab app via gitlab.localhost.com:801

I register successfully a runner with this command:

docker exec -it gitlab_gitlab-runner_1 gitlab-runner register --non-interactive --url http://gitlab_gitlab_1 --registration-token _wgMgEx3nBocYQtoi83c --executor docker --docker-image alpine:latest

Then, when I start the job, I got this error message:

Running with gitlab-runner 10.7.1 (b9bba623)
  on 589a617ee407 12ba77f7
Using Docker executor with image alpine:latest ...
Pulling docker image alpine:latest ...
Using docker image sha256:3fd9065eaf02feaf94d68376da52541925650b81698c53c6824d92ff63f98353 for alpine:latest ...
Running on runner-12ba77f7-project-1-concurrent-0 via 01196621a827...
Cloning repository...
Cloning into '/builds/root/test'...
fatal: unable to access 'http://gitlab-ci-token:[email protected]/root/test.git/': Could not resolve host: gitlab.localhost.com
ERROR: Job failed: exit code 1

In both containers, I can access to the hostname gitlab.localhost.com. I think the issue comes from the image alpine which can not resolve the host.

How can I fix that?

Thanks

Edit 1

docker-compose.yml

version: '3'
services:
  gitlab:
    image: 'gitlab/gitlab-ce:latest'
    restart: always
    hostname: 'gitlab.localhost.com'
    environment:
      GITLAB_OMNIBUS_CONFIG: |
        external_url 'http://gitlab.localhost.com'
    ports:
      - '801:80'
      - '443:443'
      - '22:22'
    volumes:
      - '/srv/gitlab/config:/etc/gitlab'
      - '/srv/gitlab/logs:/var/log/gitlab'
      - '/srv/gitlab/data:/var/opt/gitlab'
    networks:
      - 'default'

  gitlab-runner:
    image: 'gitlab/gitlab-runner:latest'
    depends_on:
      - 'gitlab'
    restart: always
    volumes:
      - '/srv/gitlab-runner/config:/etc/gitlab-runner'
      - '/var/run/docker.sock:/var/run/docker.sock'
    networks:
      - 'default'
    links:
      - 'gitlab:gitlab.localhost.com'

networks:
  default:
    driver: 'bridge'

Edit 2

docker-compose.yml

version: '3'
services:
  gitlab:
    image: 'gitlab/gitlab-ce:latest'
    restart: always
    hostname: 'gitlab.localhost.com'
    environment:
      GITLAB_OMNIBUS_CONFIG: |
        external_url 'http://gitlab.localhost.com'
    ports:
      - '801:80'
      - '443:443'
      - '22:22'
    volumes:
      - '/srv/gitlab/config:/etc/gitlab'
      - '/srv/gitlab/logs:/var/log/gitlab'
      - '/srv/gitlab/data:/var/opt/gitlab'
    networks:
      default:
        aliases:
          - 'gitlab.localhost.com'

  gitlab-runner:
    image: 'gitlab/gitlab-runner:latest'
    depends_on:
      - 'gitlab'
    restart: always
    volumes:
      - '/srv/gitlab-runner/config:/etc/gitlab-runner'
      - '/var/run/docker.sock:/var/run/docker.sock'
    networks:
      - 'default'

networks:
  default:
    driver: 'bridge'

Answer 1

Thanks to Tarun Lalwan link and according to Joyce Babu post, there are an undocumented option from the gitlab runner repos in the [runners.docker] section

network_mode : Add container to a custom network

So I have to set this option with my network name in the config.toml like

[[runners]]
  ...
  [runners.docker]
    ...
    network_mode = "gitlab_default"

OR when create the runner from command line

docker exec -it gitlab_gitlab-runner_1 gitlab-runner register \
--non-interactive \
--url http://gitlab_gitlab_1 \
--registration-token _wgMgEx3nBocYQtoi83c \
--executor docker \
--docker-image alpine:latest \
--docker-network-mode gitlab_default