Move a group to a different instance

[mayel]

"As a group admin, I want to move the group to a different instance without losing members, so the community isn't stuck on its original server."

Group portability is essential for community autonomy: if an instance shuts down, changes policies, or a group outgrows its home, the community should be able to relocate.

Existing approaches:

• FEP-7628: Proposes Move activity for actor migration with redirect
• Mastodon and others: Actor migration via Move activity + alsoKnownAs (for user accounts, not groups)
• Matrix: Room upgrades create a new room with a tombstone pointing to it

Suggested flow:

1. Setup: New group actor created on target instance, with alsoKnownAs pointing to the old group (and vice versa):

   {
     "type": "Group",
     "id": "https://new-instance.org/groups/1",
     "alsoKnownAs": ["https://old-instance.org/groups/1"]
   }

2. Announce move: Old group adds new group to alsoKnownAs and sends Move activity to all followers:

   {
     "type": "Move",
     "actor": "https://old-instance.org/groups/1",
     "object": "https://old-instance.org/groups/1",
     "target": "https://new-instance.org/groups/1"
   }

3. Follower migration: Remote instances receiving the Move:

   • Verify alsoKnownAs is set on both old and new actors (prevents hijacking)
   • Automatically re-follow the new group actor
   • Update local references (feeds, bookmarks, etc.)

4. Redirect: Old group actor continues to exist as a tombstone/redirect, responding to fetches with the new location

What must transfer:

• Followers (automatically re-following if their instance supports Move)
• Membership list (imported from old instance, manually or automatically)
• Moderator roles (attributedTo)
• Roles and permissions in interactionPolicy
• Group metadata (name, summary, icon, rules) and group settings

What should transfer:

• Content history: posts remain on original instance, attributed to original authors but can be Announced by new group

What may transfer:

• Pending moderation queues (inbox)
• Instance-level settings (e.g. blocks)

Backwards compatibility:

• Instances not understanding group Move simply lose the follow - members can manually re-follow
• alsoKnownAs on both actors prevents unauthorized moves
• Old actor can keep serving an archive of existing content

Open questions:

• Can a group be moved if the old instance is already down?
• Should members be notified and given a choice to follow to the new instance?

[trwnh]

if we define a sort of "container" or "site" for the Group then it could be made portable, yes. this has been done before with SIOC to some extent (sioc:Item is created in sioc:Container hosted by sioc:Space, more concretely a sioc:Post is created in a sioc:Forum hosted by a sioc:Site)

this does depend on relative uri support or uri rewriting though, for it to fully work. otherwise consumers won't know that the "new ids" are actually the "same as" the "old ids"