Connect CI Runner to Docker network

Summary

I have the following configuration:

dockered gitlab (named gitlab) dockered gitlab-ci-multirunner (linked to gitlab and named gitlab-runners).

     ┌──────────────────────┐  ┌─────────┐
      │      172.12.x.x      │  │172.13.x.│
     ┌┴──────────┬┬──────────┴┐┌┴─────────┴┐
     │  GitLab   ││  GitLab   ││  GitLab   │
     │           ││  Runners  ││  Runners  │
     │           ││           ││           │
     └───────────┘└───────────┘└───────────┘
          │            │    │    ▲
          │            │    │   ╱
          │            │    │  ╱
          │            │    ▼ ╱
   ───────┴────────────┴────────────────────

I successfully registered a runner into gitlab, but when I try to run a build I cannot manage to connect the docker container of the project spawned by the gitlab-runners to my gitlab docker; therefore when the project docker tries to clone the project, the runner is not able to resolve the name http://gitlab/ I tried to use the parameter -links=["network-name:gitlab"] in the toml file of my runner, but this leads to:

API error (500) Could not get container for <network name>. 

I also tried to use the extra_hosts parameter and to write the IP address of my gitlab container (this is a solution that I have found in two issues on this repo). Unfortunately, since the two containers are not in the same network this leads to a time out.

Steps to reproduce

Here is my docker compose: version: '2'

services:
  gitlab:
    container_name: 'gitlab'
    image: 'gitlab/gitlab-ce:latest'
    restart: always
    hostname: 'gitlab'
    ports:
      - '80:80'
      - '443:443'
      - '2222:22'
    expose:
      - 80
      - 443
      - 2222
    volumes:
      - '/docker/gitlab/conf:/etc/gitlab'
      - '/docker/gitlab/logs:/var/log/gitlab'
      - '/docker/gitlab/data:/var/opt/gitlab'
    networks:
      - mynet
  gitlab-runners:
    container_name: 'gitlab-runners'
    image: 'gitlab/gitlab-runner:latest'
    restart: always
    volumes:
      - '/srv/gitlab-runnes:/etc/gitlab-runner'
      - '/var/run/docker.sock:/var/run/docker.sock'
    privileged: false
    networks:
      - mynet

  gitlab-runners-data:
    external: true

networks:
  mynet:
    external: true

• mynet is a simple bridge network I created.
• multi runner has been setup so that there is a specific runner for a project that runs in docker mode.

Actual behavior

The containers generated by the multi-runner are in a different logical network, therefore the \gitlab name or its IP address are either not resolvable nor reachable.

Expected behavior

I should be able to connect the containers created by the multi-runner in the same docker network of my gitlab instance.

Environment description

• custom installation on Centos 7
• docker 1.12.2
• kernel 3-10.0-327.el7.x86_64

Used GitLab Runner version

gitlab-ci-multi-runner 1.7.1