Mirroring a repository from Gitlab to GitHub
Here's a step by step guide on how to mirror a repository from GitLab to GitHub.
- Go to your repository on GitLab, then:
 
- Settings → Repository → Mirroring repositories
 - Click on Add new
 - In the form Git repository URL, type your Github repo's URL, according to this logic:
 
ssh://github.com/[your-username]/[your-repo-name].git
- Click on Detect host keys
 - In the form Authentication method, select SSH public key
 - Click on Mirror repository.
 - By clicking the apporiate button, copy your SSH public key.
 
- On Github, go to your repository.
 
- Click on Settings → Deploy keys
 - Click on Add deploy key
 - In the form Title, type something like "deploy key" and in the form Key paste your public key.
 - Flag the field Allow write access, then click on Add key.
 
- Go back to GitLab, and go to your repository on GitLab.
 
- In Settings → Repository → Mirroring repositories, under your mirrored repository, click the Refresh button.