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This document is a work-in-progress and represents a very early state of the Cells design. Significant aspects are not documented, though we expect to add them in the future. This is one possible architecture for Cells, and we intend to contrast this with alternatives before deciding which approach to implement. This documentation will be kept even if we decide not to implement this so that we can document the reasons for not choosing this approach.

Cells: Git Access

This document describes impact of Cells architecture on all Git access (over HTTPS and SSH) patterns providing explanation of how potentially those features should be changed to work well with Cells.

1. Definition

Git access is done throughout the application. It can be an operation performed by the system (read Git repository) or by a user (create a new file via Web IDE, git clone or git push via command line). The Cells architecture defines that all Git repositories will be local to the Cell, so no repository could be shared with another Cell.

The Cells architecture will require that any Git operation can only be handled by a Cell holding the data. It means that any operation either via Web interface, API, or GraphQL needs to be routed to the correct Cell. It means that any git clone or git push operation can only be performed in the context of a Cell.

2. Data flow

The are various operations performed today by GitLab on a Git repository. This describes the data flow how they behave today to better represent the impact.

It appears that Git access does require changes only to a few endpoints that are scoped to a Project. There appear to be different types of repositories:

  • Project: assigned to Group
  • Wiki: additional repository assigned to Project
  • Design: similar to Wiki, additional repository assigned to Project
  • Snippet: creates a virtual Project to hold repository, likely tied to the User

2.1. Git clone over HTTPS

Execution of: git clone over HTTPS

sequenceDiagram
    User ->> Workhorse: GET /gitlab-org/gitlab.git/info/refs?service=git-upload-pack
    Workhorse ->> Rails: GET /gitlab-org/gitlab.git/info/refs?service=git-upload-pack
    Rails ->> Workhorse: 200 OK
    Workhorse ->> Gitaly: RPC InfoRefsUploadPack
    Gitaly ->> User: Response
    User ->> Workhorse: POST /gitlab-org/gitlab.git/git-upload-pack
    Workhorse ->> Gitaly: RPC PostUploadPackWithSidechannel
    Gitaly ->> User: Response

2.2. Git clone over SSH

Execution of: git clone over SSH

sequenceDiagram
    User ->> Git SSHD: ssh git@gitlab.com
    Git SSHD ->> Rails: GET /api/v4/internal/authorized_keys
    Rails ->> Git SSHD: 200 OK (list of accepted SSH keys)
    Git SSHD ->> User: Accept SSH
    User ->> Git SSHD: git clone over SSH
    Git SSHD ->> Rails: POST /api/v4/internal/allowed?project=/gitlab-org/gitlab.git&service=git-upload-pack
    Rails ->> Git SSHD: 200 OK
    Git SSHD ->> Gitaly: RPC SSHUploadPackWithSidechannel
    Gitaly ->> User: Response

2.3. Git push over HTTPS

Execution of: git push over HTTPS

sequenceDiagram
    User ->> Workhorse: GET /gitlab-org/gitlab.git/info/refs?service=git-receive-pack
    Workhorse ->> Rails: GET /gitlab-org/gitlab.git/info/refs?service=git-receive-pack
    Rails ->> Workhorse: 200 OK
    Workhorse ->> Gitaly: RPC PostReceivePack
    Gitaly ->> Rails: POST /api/v4/internal/allowed?gl_repository=project-111&service=git-receive-pack
    Gitaly ->> Rails: POST /api/v4/internal/pre_receive?gl_repository=project-111
    Gitaly ->> Rails: POST /api/v4/internal/post_receive?gl_repository=project-111
    Gitaly ->> User: Response

2.4. Git push over SSHD

Execution of: git clone over SSH

sequenceDiagram
    User ->> Git SSHD: ssh git@gitlab.com
    Git SSHD ->> Rails: GET /api/v4/internal/authorized_keys
    Rails ->> Git SSHD: 200 OK (list of accepted SSH keys)
    Git SSHD ->> User: Accept SSH
    User ->> Git SSHD: git clone over SSH
    Git SSHD ->> Rails: POST /api/v4/internal/allowed?project=/gitlab-org/gitlab.git&service=git-receive-pack
    Rails ->> Git SSHD: 200 OK
    Git SSHD ->> Gitaly: RPC ReceivePack
    Gitaly ->> Rails: POST /api/v4/internal/allowed?gl_repository=project-111
    Gitaly ->> Rails: POST /api/v4/internal/pre_receive?gl_repository=project-111
    Gitaly ->> Rails: POST /api/v4/internal/post_receive?gl_repository=project-111
    Gitaly ->> User: Response

2.5. Create commit via Web

Execution of Add CHANGELOG to repository:

sequenceDiagram
    Web ->> Puma: POST /gitlab-org/gitlab/-/create/main
    Puma ->> Gitaly: RPC TreeEntry
    Gitaly ->> Rails: POST /api/v4/internal/allowed?gl_repository=project-111
    Gitaly ->> Rails: POST /api/v4/internal/pre_receive?gl_repository=project-111
    Gitaly ->> Rails: POST /api/v4/internal/post_receive?gl_repository=project-111
    Gitaly ->> Puma: Response
    Puma ->> Web: See CHANGELOG

3. Proposal

The Cells stateless router proposal requires that any ambiguous path (that is not routable) will be made routable. It means that at least the following paths will have to be updated to introduce a routable entity (Project, Group, or Organization).

Change:

  • /api/v4/internal/allowed => /api/v4/internal/projects/<gl_repository>/allowed
  • /api/v4/internal/pre_receive => /api/v4/internal/projects/<gl_repository>/pre_receive
  • /api/v4/internal/post_receive => /api/v4/internal/projects/<gl_repository>/post_receive
  • /api/v4/internal/lfs_authenticate => /api/v4/internal/projects/<gl_repository>/lfs_authenticate

Where:

  • gl_repository can be project-1111 (Gitlab::GlRepository)
  • gl_repository in some cases might be a full path to repository as executed by GitLab Shell (/gitlab-org/gitlab.git)

4. Evaluation

Supporting Git repositories if a Cell can access only its own repositories does not appear to be complex. The one major complication is supporting snippets, but this likely falls in the same category as for the approach to support a user's Personal Namespace.

4.1. Pros

  1. The API used for supporting HTTPS/SSH and Hooks are well defined and can easily be made routable.

4.2. Cons

  1. The sharing of repositories objects is limited to the given Cell and Gitaly node.
  2. Cross-Cells forks are likely impossible to be supported (discover: How this works today across different Gitaly node).