What is the fastest way to sync code between gitlab-servers ?

I deploy gitlab-ce on my computers/dockers.

In fact, I deploy two gitlab-ce servers because I have many users and very poor computers.

I have to sync repository between server1 and server2.

Now the problem come, when user_A push code to server1 , he find his CI can't get code from server2 immediately.

gitlab.com have many servers all over the world and it can sync code so efficiently.

I use git hook to sync code between gitlab-servers, but it seems take some time.

Thank you very much!