Yes, I’m certain I could final answers to all these questions via research, but I’m coming here as part of the Reddit diaspora. My guess is that there’s a benefit to others like me to have this discussion.
I can vaguely understand the federation concept, the idea that my account is hosted at an individual Lemmy server and that other servers trust that one to validate my account. What’s the network flow like? I’m posting this to the lemmy.ml /asklemmy community, but I’m composing it on the sh.itjust.works interface. I’m assuming sh.itjust.works hands this over to lemmy.ml. How does my browsing work? Is all of my traffic routed through sh.itjust.works?
Assuming there’s a mass influx of redditors, what does it look like as things fail? I’m assuming some servers can keep up under the load and some can’t. If sh.itjust.works goes down under the load, can I still browse other servers? Or, do those servers think I should have some token from sh.itjust.works, because my cookies say I’m still logged in, and I can’t even do that?
Are there easy mechanisms to allow me to grab my post history?
I’m assuming most (all?) Lemmy servers are hosted in home labs? The idea of Lemmy excites me, but the growth pain that could be coming scares me. Anybody using a CDN in front of their servers? That could be good, but with unconstrained growth, that could be costly, which is very bad.
I can imagine lots of different worse case scenarios, but I’m curious what those of you who run servers imagine for the best case scenario? A manageable growth that just gets more vibrant communities, which can’t ever lead to the breadth and variety of Reddit?
Also, for those running servers, have any of you experienced issues during this growth? What scares you?
So, you post and it federates from your instance to lemmy.ml where the group you're posting to resides.
Then the group basically "boosts" your post, and anyone that follows the group (ie, anyone that is subscribed to it) sees the "boost", which the lemmy interface then displays as a post in the group. But if you follow the group from mastodon/calckey etc, instead of a threadiverse app, then it would just appear as a regular boost by the group you posted to.
Backfilling of data isn't really a thing as such. Basically, your instance is only aware of content that has federated to it, and it only starts federating to your instance when someone first subscribes to a particular group.
That being said, the devs have mentioned that when lemmy federates the group actor, the API also sends the last 20 posts to the group. I don't know how often groups are updated, and whether this applies every time it's refreshed or not though...