This site is currently struggling to handle the amount of new users. I have already upgraded the server, but it will go down regardless if half of Reddit tries to join.
However Lemmy is federated software, meaning you can interact seamlessly with communities on other instances like beehaw.org or lemmy.one. The documentation explains in more detail how this works. Use the instance list to find one where you can register. Then use the Community Browser to find interesting communities. Paste the community url into the search field to follow it.
You can help other Reddit refugees by inviting them to the same Lemmy instance where you joined. This way we can spread the load across many different servers. And users with similar interests will end up together on the same instances. Others on the same instance can also automatically see posts from all the communities that you follow.
Edit: If you moderate a large subreddit, do not link your users directly to lemmy.ml in your announcements. That way the server will only go down sooner.
I'm not sure why you think the setup I've described can't have coverage in multiple availability zones. If the lemmy and lemmy-ui containers are stateless as I suspect, you can autoscale them. Pictrs is new to me, not sure there... but it appears to support object-storage which would likely make it stateless and the object-storage can replicate to multiple-az's. Postgres read-replicas can be placed in multiple az's as well. The only component that presents an issue is the Postgres write-leader, and failovers there can be done in minutes. Many many popular sites run with an infrastructure like this and achieve excellent uptimes.
I do get the power of horizontal scalability, I specialize in distributed databases. But they come at a cost in flexibility relative to something like Postgres... and we're very far from "needing" horizontally scaling database writes here. Everything else looks like it can be scaled horizontally if someone wants to take on the headache of doing so.
Well, one could try to swap postgres for cockroachdb. But a ticket in github that asked for clustering support was closed with being out of scope. So might be lemmy is not stateless. Haven't checked the code yet, though.
If cockroach is truly PG compatible, lemmy admins can swap it in without developer support. I suspect Cockroach constrains some SQL features and has poor performance on others, but that or AWS Aurora are things you can experiment with without dev support if you're passionate about the proving out the value of scale-out.
The statement that spawned my response though was this:
I still don't think it's true that we need horizontal scaling to support sufficiently large instances. The amount of vertical and horizontal scaling ability built into Lemmy today is both useful, and likely to outstrip the current ability of its code to scale a single instance. Any algorithms that scale super-linearly with respect to comment-count, post-count, user-count, or community-count, will fail just as hard with distributed backends as they do with an RDBMS. And as you note, PG-compatible distributed systems provide a potential lower-engineering-cost on-ramp to distributed systems once the codebase is efficient-enough to warrant such a transition to scale further. I suspect I've contributed everything of use I have to this thread though, and don't expect to respond further.
As someone not versed in DBs and scaling for web architecture, this was a super fun read through, appreciate the comment chains from both users.
Thank you for your thorough explanations and input. It definitely gave me a few things to think about. And if I have some spare time I might even try to spin up lemmy in some local k8s to see how it reacts to being scaled up and down.