How to setup gitlab-runner to run docker command into gitlab-ci?

According to @Dr Claw and @vpalmerini comments, it necessary to add docker.sock into volume and remove variables and service. See this thread.

My .gitlab-ci.yml :

variables:
  DOCKER_DRIVER: overlay2

before_script:
  - df
  - cat /etc/resolv.conf
  - cat /etc/hosts

deploiement:
  image: docker:latest
  before_script:
    - docker version
  script:
    - docker info

My config.toml:

[[runners]]
  name = "Synology premier runner"
  url = "http://my.domain.com:8484/"
  token = "1UsxGPQmxht6zHPb_y2b"
  executor = "docker"
  clone_url = "http://my.domain.com:8484/"
  [runners.custom_build_dir]
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    tls_verify = false
    image = "node:lts-alpine"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/var/run/docker.sock:/var/run/docker.sock", "/cache"]
    shm_size = 0

Thanks you very much for your answers @Dr Claw and @vpalmerini !

I like to share my config for docker rootless. It is very similar to the one provided by Jérémy.

1. Prepare a linux machine with a docker rootless installation.

2. SSH to your host and become the "docker" user that is allowed to execute docker command.

3. Find your user id by typing id. Let´s say it gives you a 1004.

4. Start a gitlab-runner container using a socket mount from your user directory /run/user/1004

   docker run -d --name gitlab-runner --restart always -v /run/user/1004/docker.sock:/var/run/docker.sock -v gitlab-runner-config:/etc/gitlab-runner gitlab/gitlab-runner:latest
   

5. Register the runner

docker run --rm -t -i -v /srv/gitlab-runner/config:/etc/gitlab-runner --name gitlab-runner gitlab/gitlab-runner register

6. It will ask for some information.

• If your repo or group is on gitlab, simply use "https://gitlab.com" as runner address. You don´t need to get more specific.

• Get your token. Go to your group or project on gitlab. Find the “runners” entry in the “Build” menu.

  Add a new runner and copy the token to an editor or leave the page open for further reference.

• User docker as executor

7. Now the runner should be connected. You can configure it to your gitlab project project/settings/ci

8. To make docker in docker work I use the following config on the host ~/.local/share/docker/volumes/gitlab-runner-config/_data/config.toml

concurrent = 1 # Bump this up to allow more than one job to run in parallel 
check_interval = 0
shutdown_timeout = 0
[session_server]
  session_timeout = 1800
[[runners]]
  name = "my-runner"
  url = "https://gitlab.com/"
  id = 47413623
  token = "XXX-your-token-here-XXX"
  token_obtained_at = 2025-05-12T06:29:10Z
  token_expires_at = 0001-01-01T00:00:00Z
  executor = "docker"
  [runners.cache]
    MaxUploadedArchiveSize = 0
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    tls_verify = false
    image = "docker:latest"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache",,"/run/user/1004/docker.sock:/var/run/docker.sock"]
    shm_size = 0
    network_mtu = 0

9. Example with three files: .gitlab-ci.yml, Dockerfile, index.md

.gitlab-ci.yml

...

Docker Build:
  image: docker:latest 
  services:
    - docker:dind 
  variables:
    DOCKERFILE: Dockerfile
    IMAGE_NAME: $CI_PROJECT_NAME
    IMAGE_TAG: $CI_COMMIT_SHORT_SHA
    IMAGE_URI: ${CI_REGISTRY_IMAGE}/${IMAGE_NAME}:${IMAGE_TAG}
  before_script:
    - unset DOCKER_HOST
    - docker login -u "gitlab-ci-token" -p "$CI_JOB_TOKEN" "$CI_REGISTRY"
  script:
    - docker build --quiet --pull -f $DOCKERFILE -t $IMAGE_NAME:$IMAGE_TAG .
    - docker image tag ${IMAGE_NAME}:${IMAGE_TAG} $IMAGE_URI
    - docker push $IMAGE_URI  
...

Dockerfile

FROM registry.gitlab.com/schnasse-org/docker-build/quarto:0.1.1 AS build
COPY index.md /mysite/
RUN quarto render /mysite --output-dir /usr/share/nginx/html

FROM nginx:latest
COPY --from=build /usr/share/nginx/html /usr/share/nginx/html
EXPOSE 80

index.md

# Hello World 

10. Docker Compose

docker-compose.yml

services:
  gitlab-runner:
    image: gitlab/gitlab-runner:latest
    restart: always
    container_name: gitlab-runner
    volumes:
      - gitlab-runner-config:/etc/gitlab-runner
      - /run/user/1004/docker.sock:/var/run/docker.sock
volumes:
  gitlab-runner-config: