Configure gitlab-runner using a Dockerfile - docker

Question

I'm trying to write-down a Dockerfile to create create and register a new runner to a private gitlab repository. According to gitlab documentation, I wrote down the following Dockerfile:
FROM gitlab/gitlab-runner:latest
RUN gitlab-runner register \
--non-interactive \
--url "https://gitlab.com/" \
--registration-token "GITLAB_REPO_TOKEN" \
--executor "docker" \
--docker-image alpine:latest \
--description "docker-runner" \
--maintenance-note "Free-form maintainer notes about this runner" \
--run-untagged="true" \
--locked="false"
Then build it with:
docker build -t test .
And then run it in a container via:
docker run test:latest
The runner is correctly seen by gitlab (the runner is available under Settings\CI/CD\Runners).
Then, I set up the following CI, for testing:
image: python:3.7-alpine
testci:
stage: test
script:
- python test.py
The job is then pulled by the runner, but I immediately get the following error:
Running with gitlab-runner 15.8.2 (4d1ca121)
on docker-runner yVa1JDny, system ID: xxxxxxxxx
Preparing the "docker" executor
00:09
ERROR: Failed to remove network for build
ERROR: Preparation failed: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? (docker.go:753:0s)
Can anyone please provide support in that? I didn't get what it is missing from the configuration I've made.
I've tried to modify the docker run call trying with the volume mount guide found here, but nothing changes.
I've also found here a similar Dockerfile, but using a gitlab-ci-multi-runner which is not the desired service.

Answer 1

You're attempting to use the docker executor for your runner, but your runner doesn't have access to the docker socket in order to create new containers. Your runner manager (what your docker file is creating) is attempting to start up new docker containers to handle each of your jobs, but failing to connect to docker.
In your docker run command, you will need to do a couple things:
Set your container to use privileged mode: --privileged
Map in the docker socket: -v /var/run/docker.sock:/var/run/docker.sock
With those two things, you can likely connect to the docker daemon and start new containers. If you want to perform docker builds within CI using this runner, note you'll need to configure your runner manager (again, what your docker file is creating) to allow these same two settings on the build containers. You can get information about how to do that here: https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#use-docker-socket-binding