> I want to keep all the usernames and external follow relationships intact ActivityPub doesnt have the concept of a "username" in the sense that you are think

> I want to keep all the usernames and external follow relationships intact ActivityPub doesnt have the concept of a "username" in the sense that you are thinking. An activitypub "preferredUsername" field is just a preferred display name for that actor. Instead they have actor ids - which are just URIs. Behind the scenes, mastodon (and similar) simply treat @me@myserver.example.com as a webfinger ref. They do a lookup via webfinger which returns the actor id, and then they connect to that URI to return the respective object(s). Of course, because your mastodon instance is also likely hosting your actor AND its respective collections AND its activities, then ALL the URIs are ALSO tied to their domain. In order to "migrate" they (probably - im not 100% sure) send updates for your actor object (and your other activity types) to your outbox and distribute to your followers, who will then update their own references to your actor, its aliases (such as the webfinger ref), and other associated collections and activities. Its 100% possible to have a webfinger alias on your own domain and use separate hosts for your actor, specific collections, and each individual activity, should you wish. Mastodon can reach other activitypub actors and activities configured in this way, but it cant provide a similar service for its own users, due to its current implementation (it expects to be the originator of activities for its associated actors).