Ref

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• https://github.com/gitblit/gitblit

[at15]

• gitbucket use apache sshd to handle ssh connection https://github.com/gitbucket/gitbucket/tree/master/src/main/scala/gitbucket/core/ssh

[at15]

• gitlab's architecture http://doc.gitlab.com/ee/development/architecture.html

The add-on component gitlab-shell serves repositories over SSH. It manages the SSH keys within /home/git/.ssh/authorized_keys which should not be manually edited. gitlab-shell accesses the bare repositories directly to serve git objects and communicates with redis to submit jobs to Sidekiq for GitLab to process. gitlab-shell queries the GitLab API to determine authorization and access.

so gitlab shell hook into the system ssh server and use GitLab API for auth, while gitbucket use java and check directly inside the application.