Right now, users are allowed to delete a remote anytime. The deletion can disrupt content artifacts that contain the reference to remote artifacts associated with the remote.
When a remote is deleted (and there is no other backup left - another remote) the publication machinery in pulp_file fails because it cannot fetch the URL for any of the synced content units.
To prevent such from happening, we propose adding a check hooked to the PRE_DELETE signal to disallow the removal of a remote when no other remote artifacts are left. This forces users to delete all synced repositories and synced content before deleting the actual remote. As a result, content artifacts will not end up in an inconsistent state.
- The solution adds more burden on users when deleting regular remotes.
- The solution may not be performance efficient since we need to check all content artifacts to have at least one remote artifact.
- The solution does not guarantee that in the future we will have more than one remote artifact per content artifact (then considering
on_delete=PROTECTwould be an option as well: Should we keep using FK with on_delete=SET_NULL?).
Remote artifacts are created during the sync procedure when the on-demand policy is used. When a user syncs a repository with two remotes pointing to the same destination, two remote artifacts per one content artifact are created:
pulp file remote create --name remo11 --url https://fixtures.pulpproject.org/file/PULP_MANIFEST --policy on_demand pulp file remote create --name remo1 --url https://fixtures.pulpproject.org/file/PULP_MANIFEST --policy on_demand pulp file repository create --name repo pulp file repository sync --name repo --remote remo1 pulp file repository sync --name repo --remote remo11
So, in this case, removing one of the remotes will not cause any harm. Removing both of the remotes will cause the publication machinery to fail. The proposed protection does not allow users to delete both of the remotes.
The proposed solution comes from Problem: Deleting Remote deletes RemoteArtifacts - HackMD (1c). The PR that implements the solution is available at https://github.com/pulp/pulpcore/pull/2836.