There are no "the Lemmy servers", since there is no central "Lemmy" organization to host and run such servers.
So yeah, you can run it on whatever you can find that has available disk space, CPU cycles, and an Internet connection. Hosted VPS, colocated hardware server, raspberry pi, your gaming rig, AWS containers, whatever.
Or, to put it in a simple one-liner: Instances are servers.
However you would set up any other server, you set up a Lemmy instance. There is no central datacenter as there would be with a corporate-owned site like Reddit.
Think of it like a bunch of little messages board sites and they automatically import posts from other message board sites - because that’s exactly what it is.
While that’s a bit different to navigate than what we are used to, an instance (aka a server) going down or becoming hostile and being defederated only removes that one server from the network.
It’s similar to how IRC networks function; except with those, the server owners decide what servers they link up with. With Lemmy (and other ActivityPub based services), the users decide (by subscribing). Instance admins can block (“defederate”) other instances though.
lemmy can run on a decent variety of hardware, just has to be some thing left on 24/7 and exposed to the internet (be careful, the internet is a hostile place... mine was getting scanned and poked constantly until I put it behind cloudflare and then locked the firewall down to just let in cloudflare), and of course more users take more powerful hardware.
For my personal just me instance though, I'm just running it on a Raspberry Pi 4 I run some other stuff on. Uses less than a gig of memory.
The Pi4 is a pretty impressive little machine. It'll probably host a few users, but from what I understand, it's the federation that really starts scaling the requirements.
Bigger problem with the Pi though is that it runs off an SDcard (by default), which have limited writes, and you'll burn that up fast.
It has the power to run a one user instance, I'm sure it would run into issues trying to squeeze a normal amount of people onto it, but a handful sure.
Running my own instance for our community (on a cheap Synology NAS) was something my dumbass considered when making the move here from Reddit. I'm glad I didn't and just left it to the professionals, seeing as even experienced admins like Ruud have trouble with DDoS attacks and other shit.
You’ll need to have some kind of monitoring in place. Firewall logs, packet capture (i.e. wireshark), security onion, and a bunch of other security logging/monitoring tools. If you’re hosting on the cloud, your provider may have some free tools you can use (i.e. CASB).
normally you'd rent out a server (vps) and run it on there but hosting from your house would also work. the whole idea about Lemmy is that each instance is ran on different servers by different people
I'd be hesitant to run it at your own house. While you can use a cloudflare tunnel, I'd never expose anything in my home network to the outside.
Digital ocean is cheap, there's another called hetzner which looks also pretty cheap. So you start will rent 1 core VPS for 5 bucks, it's enough to run your own instance but not really enough to host any communities.
In most cases, you'd rent a VPS (Virtual Private Server) from one of numerous providers who have data centres all over the world.
It's possible to host an instance at your home or whatever but residential internet connections are usually noticeably slower for people accessing them remotely.
One of the main benefits of decentralised platforms like lemmy is that everyone has the option to host their stuff on hardware they control. Even if you're using a VPS in a data centre somewhere, you have some level of control.