SSH git push to secondary -> proxy to Primary

What does this MR do?

This MR implements the necessary logic to detect when an SSH git push is attempted to a secondary and proxys the HTTP equivalent requests to the primary and responds back the git client with the appropriate response.

• Two new Geo API methods:
  • /api/vX/geo/proxy_git_push_ssh/info_refs - Calls Gitlab::Geo::GitPushSSHProxy#info_refs
  • /api/vX/geo/proxy_git_push_ssh/push - Calls Gitlab::Geo::GitPushSSHProxy#push
• New Gitlab::Geo::GitPushSSHProxy class which contains:
  • #info_refs - Calls HTTP GET /repo.git/info/refs?service=git-receive-pack on primary
  • #push - Calls HTTP POST /repo.git/git-receive-pack on primary

Are there points in the code the reviewer needs to double check?

• ee/lib/ee/gitlab/geo_git_access.rb#check_db_accessibility! is thoroughly examined
• ee/lib/gitlab/geo/git_push_ssh_proxy.rb#remove_http_service_fragment_from! is thoroughly examined
• Suitable tests exist
• Suitable API documentation added/updated
• FIXMEs addressed

⚠ Needed Dependencies ⚠

• gitlab-shell!214 (merged) - Refactor that focuses on SRP improvements
• gitlab-shell!215 (merged) - Custom Action support
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21038 - Allow auth via JWT (always false in CE)
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21034 - Custom Action support
• https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6455 - Allow push_code when auth'd via Geo JWT
• Then, this MR :)

Why was this MR needed?

To facilitate the proxying of SSH git push requests sent to the primary, from the secondary https://gitlab.com/gitlab-org/gitlab-ee/issues/6533

Screenshots (if relevant)

Current

sequenceDiagram
  participant Client
  participant Secondary
  participant SecondaryGitaly as Secondary gitaly
  participant SecondaryGitLabShell as Secondary gitlab-shell
  participant Primary
  Note over Client,Secondary: $ git push
  Client->>SecondaryGitLabShell: ssh <single> git-receive-pack ''/repo.git''
  SecondaryGitLabShell->>+Secondary: HTTP POST /api/v4/internal/allowed
  Secondary-->>-SecondaryGitLabShell: NOTOK
  Note over SecondaryGitLabShell,Client: "You can't push code to a read-only GitLab instance.  Please use the primary node URL instead .."

.

New

sequenceDiagram
  participant Client
  participant Secondary
  participant SecondaryGitLabShell as Secondary gitlab-shell
  participant Primary
  Note over Client,Secondary: $ git push
  Client->>SecondaryGitLabShell: ssh <single> git-receive-pack ''/repo.git''
  SecondaryGitLabShell->>+Secondary: HTTP POST /api/v4/internal/allowed
  Secondary-->>-SecondaryGitLabShell: OK, REDIRECT
  SecondaryGitLabShell->>+Secondary: HTTP POST /api/v4/geo/proxy_git_push_ssh/info_refs
  Secondary-->>Primary: HTTP GET /repo.git/info/refs?service=git-receive-pack
  Primary-->>Secondary: <refs>
  Secondary->>-SecondaryGitLabShell: <refs>
  SecondaryGitLabShell->>+Secondary: HTTP POST /api/v4/geo/proxy_git_push_ssh/push
  Secondary-->>Primary: HTTP POST /repo.git/info/refs?service=git-receive-pack/git-receive-pack
  Primary-->>Secondary: <refs>
  Secondary->>-SecondaryGitLabShell: <refs>
  SecondaryGitLabShell-->>+Client: <refs>

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • [ ] Has been reviewed by a UX Designer
  • [ ] Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • [ ] Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• [ ] Conform by the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• [ ] Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/6533