Gitlab runner, docker registry and self-signed certs I've set up a Gitlab registry with self-signed certificate. After that I had to convince docker app to trust my CA, I did this by putting CA.crt into 

/etc/docker/certs.d/registry.gitlab.yourdomain:5000


But you have to convince docker executor and dind service in Gitlab Runner too, I've done this by passing cert through volumes in config.toml:

volumes = ["/cache", "/certs/client", "path/to/cert/ca.crt:/etc/docker/registry.gitlab.yourdomain:5000/ca.crt"]


See the problem? Gitlab Runner uses old volume specification, so :5000 part will break it. I know about existence of pre_clone_script, so that you can map your cert into some folder and then move it. But that will not solve the dind service problem - pre_clone_script will only be executed in 'main' container.
Oh well, the answer was simple: why do you need to use volume only for file transfer? Just volume the directory, containing problematic folder with cert in it.