where do the instances actually reside?

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.

Brb, taping some PS3's together.
- if only I hadn't bricked my jailbroken ps3. rust should be able to compile down to ppc64le Linux binaries
Can’t wait for someone to run an instance on a homebrewed DS and see people asking why “lemmy.ds is down all the time??”
- Or a Samsung fridge.
  The race is open!
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.

In your heart ❤️

This is the only thing that makes sense, considering everyone is a bot except me.
- That sounds like something a bot would say.

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.

A pi4 has the power for it? I would assume Lemmy would chew into the drive space
- 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.
- So you would just add another (or larger) drive, right? A Pi itself doesn't even have a drive.
- 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.
  I run everything off an external hard drive
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.
How can I tell if my instance is being probed for security issues?
- There is no need to check. Everything exposed to the internet is being scanned. (The only exception is maybe IPv6 with no specific TLS cert.)
- 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).
- Assume it is.

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.
- I host a few purely personal services exposed to the net....
  But when I wanted to set up a lemmy instance I got a VPS. Too public.
  And since I had more resources than I needed I opened it for others to register too :)
  At least one user has surpassed me in number of comments (~600) so I helped the fediverse a bit
- Yeah, most likely your ISP will just stop you. Home internet plans in the US today almost all disallow using the service for public hosting.
- +1 for Hetzner. Their servers are reliable and reasonably cheap.

A Lemmy instance runs on a computer (server) and that server could be anything from a VPS you rent to your own computer in your home.

My instance is hosted on my own hardware, at my home.

Usually high up in the clouds.

Very high indeed, you need "grass" to get up there.
- Hey that's not entirely fair

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.

Did you have a look at this guide? https://lemm.ee/post/37715

I'm running a Pixelfed instance off of an old PC in my house. Eventually I 'd like to set up a personal Lemmy instance as well.

Mine is on a server I rent but there's absolutely no reason it can't be in my house. My other federated servers are.

"lemmy" itself is just a type of website we call instances, so people and organization host it themselves in the place of their choice