Registrar o runner e criar o container para execução
docker run -it --name <container-name> \
-v /var/run/docker.sock:/var/run/docker.sock \
-v /srv/gitlab-runner/config:/etc/gitlab-runner \
gitlab/gitlab-runner register
Após responder as questões informando endereço e token
Iniciar o container
docker start <container-name>
Executar comandos do runner no container
docker exec -it <container-name> gitlab-runner <comando>
# Ex.:
docker exec -it <container-name> gitlab-runner start