If an instance were to leave the fediverse do we loose all its data? Say for example iPad Lenny.ml domain was seized or was forced to shutdown so we loose all communities from that host? Do we not see any posts? Can we still post to it? Seems like a big flaw if we have multiple large instances that can shutdown a significant portion of Lemmy.
We lose the communities from that instance, yes. And that’s why people want to make sure you don’t have one dominant instance on the threadiverse. But frankly that issue will be there unless you have a fully decentralised system.
That being said, other instances will have a cache of the activities happening on this other instance. You can then fairly easily recreate it from this cache, and if you have a lot of storage, can also have a limitless cache.
It is indeed a flaw, though it is in itself already a fix for the single-instance services, such as Reddit.
If an instance becomes unavailable/defederated on the fediverse, a large portion of content will become unavailable, but the service will still be functional. If a single-instance service becomes unavailable, or if the admins do something stupid, ALL data will be jeopardized.
I know that this might not be the answer you seek, but I think it helps adding perspective to the problem.
If an instance goes down (permanently), federation of all of the communities hosted by that instance essentially stop. The content that has already been posted remains but anything new added to those communities only remain on your home instance. The only way for federation to resume is for that instance to come back online with the same domain it started with.
Lenny? Lenny?
If we lose Lenny we still have Carl.
