Gitlab-runner docker executor with dind.

config.toml

concurrent = 5
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "Docker runner"
  url = "https://gitlab.com/"
  token = "<token>"
  executor = "docker"
  privileged = true
  [runners.custom_build_dir]
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    tls_verify = false
    cache_dir="/cache"
    image = "docker:19.03.12"
    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

The bind "/var/run/docker.sock:/var/run/docker.sock" is needed (issue) my guess is that the gitlab-runner docker creates this bind using de config.toml.