Synchronizing two gitlabs


I have a gitlab installation in my company’s secure network. I would like to share some of the projects with an external partner. I want them to push code as well as create issues.

I was thinking it would be good to have those projects mirrored in another machine accessible from outside. But this mirroring needs to be two ways, I want them to access the issues that I create, and I want to access the issues that they create.

Maybe I can have two gitlab installations that talk each other and syncs everything related to some specified projects?

Does anybody know how to do this? I am also open to other solutions that you guys can think of.