gitlab-sshd in GitLab Shell
gitlab-sshd is a binary in gitlab-shell
which runs as a persistent SSH daemon. It is intended to replace OpenSSH on GitLab SaaS,
and eventually other cloud-native environments. Instead of running an sshd process,
we run a gitlab-sshd process that does the same job, in a more focused manner:
sequenceDiagram
participant Git on client
participant GitLab SSHD
participant Rails
participant Gitaly
participant Git on server
Note left of Git on client: git fetch
Git on client->>+GitLab SSHD: ssh git fetch-pack request
GitLab SSHD->>+Rails: GET /internal/api/authorized_keys?key=AAAA...
Note right of Rails: Lookup key ID
Rails-->>-GitLab SSHD: 200 OK, command="gitlab-shell upload-pack key_id=1"
GitLab SSHD->>+Rails: GET /internal/api/allowed?action=upload_pack&key_id=1
Note right of Rails: Auth check
Rails-->>-GitLab SSHD: 200 OK, { gitaly: ... }
GitLab SSHD->>+Gitaly: SSHService.SSHUploadPack request
Gitaly->>+Git on server: git upload-pack request
Note over Git on client,Git on server: Bidirectional communication between Git client and server
Git on server-->>-Gitaly: git upload-pack response
Gitaly -->>-GitLab SSHD: SSHService.SSHUploadPack response
GitLab SSHD-->>-Git on client: ssh git fetch-pack response