• Clone the repository & deploy the compose file gitlab-runners.yml as a stack, after you have configured you preferred settings (e.g. variables, secrets, replicas etc.)

docker stack deploy -c gitlab-runners.yml <stack-name>

• You can scale gitlab runners up, using docker service scale <stack-name>_runner=<number-of-replicas>

All variables can be referenced in Official Docker Runner Registration Options and/or running command gitlab-runner register -h

• GITLAB_URL: GitLab instance URL, can also be deployed as a Swarm secret target: gitlab_url. Default value: https://gitlab.com/
• PROJECT_REGISTRATION_TOKEN: token you obtained to register the Runner, can also be deployed as a Swarm secret target: project_registration_token.
• RUNNER_EXECUTOR: Runner executor - Valid values: ssh, docker+machine, docker-ssh+machine, kubernetes, docker, parallels, virtualbox, docker-ssh, shell. Default docker
• DOCKER_DEFAULT_IMAGE: If you chose Docker as your executor, you’ll be asked for the default image to be used for projects that do not define one. Default: docker:latest
• RUNNER_DESCRIPTION: Enter a description for the Runner.
• TAG_LIST: Gitlab-Ci tags for this runner - comma separated. Default: docker
• RUN_UNTAGGED: Register to run untagged builds. Default: true
• LOCKED: Lock Runner for current project. Default: false
• DOCKER_PRIVILEGED: Give extended privileges to container. Default: true
• ACCESS_LEVEL: Set access_level of the runner to not_protected or ref_protected. Default: not_protected
• DOCKER_VOLUMES_LIST: Bind-mount one or more volumes and create it/them if doesn't exist prior to mounting - comma separated. Example: /var/run/docker.sock:/var/run/docker.sock (binds to default docker socket in the host)

Do not forget to also add the volumes specified in DOCKER_VOLUMES_LIST, to the volumes section in compose file.