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[Search the codebase for `maintenance_mode?`.](https://gitlab.com/search?search=maintenance_mode%3F&group_id=9970&project_id=278964&scope=blobs&search_code=false&snippets=false&repository_ref=)
- [the read-only database method](https://gitlab.com/gitlab-org/gitlab/-/blob/2425e9de50c678413ceaad6ee3bf66f42b7e228c/ee/lib/ee/gitlab/database.rb#L13), which toggles special behavior when we are not allowed to write to the database. We use this method for possible places where writes could occur in GET requests. [Search the codebase for `Gitlab::Database.read_only?`.](https://gitlab.com/search?search=Gitlab%3A%3ADatabase.read_only%3F&group_id=9970&project_id=278964&scope=blobs&search_code=false&snippets=false&repository_ref=)
- [the read-only middleware](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/lib/ee/gitlab/middleware/read_only/controller.rb), where HTTP requests that cause database writes are blocked, unless explicitly allowed (for example, GET requests).
- [Git push access via SSH is denied](https://gitlab.com/gitlab-org/gitlab/-/blob/2425e9de50c678413ceaad6ee3bf66f42b7e228c/ee/lib/ee/gitlab/git_access.rb#L13) by returning 401 when `gitlab-shell` POSTs to [`/internal/allowed`](internal_api/index.md) to [check if access is allowed](internal_api/index.md#git-authentication).
- [Container registry authentication service](https://gitlab.com/gitlab-org/gitlab/-/blob/2425e9de50c678413ceaad6ee3bf66f42b7e228c/ee/app/services/ee/auth/container_registry_authentication_service.rb#L12), where updates to the container registry are blocked.
The database itself is not in read-only mode (except in a Geo secondary site) and can be written by sources other than the ones blocked.
