In the first versions of GitLab, all Git operations relied on using a local disk or network share. Gitaly is a project that tries to eliminate reliance on the Network File System (NFS). Instead of calls to a filesystem service, Gitaly provides GitLab with a system based on Remote Procedure Calls (RPCs) to access Git repositories. It is written in Go and uses gRPC Remote Procedure Call (gRPC), a cross-platform RPC framework from Google. It has been steadily developing since the beginning of 2017, and since GitLab 11.4, it can replace the need for a shared NFS filesystem.
You can find an overview of Gitaly and its place in the GitLab architecture in the following screenshot:
On a small installation, it runs in the same servers as all other components. In big clustered environments, you can set up dedicated Gitaly servers, which can be used by Gitaly clients such as the following:
- Unicorn
- Sidekiq
- gitlab-workhorse
- gitlab-shell
- Elasticsearch indexer
- Gitaly as a client
The source code of this project can be found here: https://gitlab.com/gitlab-org/gitaly.