Coincidentally, I just finished setting up Gitlab and Gitlab CI on a private server. If I could set up repo mirroring between it and Github, it would add a layer of protection for getting critical work done (security by distribution?).
[remote "origin"]
url = https://github.com/somerepo.git
url = https://gitlab.yourdomain.tld/somerepo.git
fetch = +refs/heads/*:refs/remotes/origin/*
What happens if the repos aren't in sync and you pull?
Edit: curiosity got the better of me https://gist.github.com/mitchty/0c2089445c1400d46cb9
Basically exactly what you'd think.