> What do you think would happen if the Bluesky company suddenly blocked everyone but
https://bsky.app/ servers from using their relays?
That's not how it works. Appviews pick the relay they use, not the client/user. The relay is used for gossip into the appview (and other things).
More importantly, appviews never see the client/user directly. Appviews only talk to the PDS. Really most things other than the client ever only talk to the PDS or listen to the relay. The only thing that ever directly talks to the client is the PDS.
The way atproto services generally work is the client configures a series of XRPC requests with HTTP headers to determine what appview, labelers, etc to use and it issues that request to the PDS. The PDS then proxies that request to the appview or wherever and they respond back to the PDS which routes the response back to you.
So in a real sense your PDS is not just a data host, but also operates akin to an IRC bouncer.
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> And what if, before they did that, they updated the PDS code so it blocked all relays except for their one?
PDS relay routing, etc is mostly all handled manually via config files,etc so this isn't really a concern. And PDS code is probably the "easiest" part of the ecosystem to hack on which is why there are like 6 different implementations with the majority (like 4) that maintain near feature parity with the "bluesky PDS" software.
And importantly, the bluesky PDS is literally a sqlite DB, an OAUTH implementation, some go IPLD data structure manipulation code, and a go XRPC router. It's fairly trivial to hack on as needed.
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> I'm not asking what you would do. I'm asking what would happen because of what everyone does. I think the name "Bluesky" would refer to the fully centralized bsky.app [...]
Migration currently isn't perfect but within ~6 months it should be ironed out by the community at which point migrating off a PDS to another is just a matter of:
1. click button on new PDS to transfer/"create new account".
2. set your new email, password, and list your old/current handle.
3. get auth code via email (one from the new PDS and one from your DID provider)
4. input codes into migrator interface (for whichever migrator you are using)
5. log into your apps again.
There are multiple large PDS operators working really really hard to spin up operations (proper backups, failover, HA, etc) so they can run reliably and avoid the "my mastodon instance imploded guess everything is gone" issue. Open federation is only about ~ a year old (plus change) so the community is only just now really reaching the "mature third parties" stage.