I know that Lemmy is open source and it can only get better from here on out, but I do wonder if any experts can weigh in whether the foundation is well written? Or are we building on top of 4 years worth of tech debt?
I disagree that it being a monolith is immediately a problem, but also
In fact you scale a monolith the same way you scale micro services.
This is just not true. With microservices, it is easy to scale out individual services to multiple instances as demand requires them. Hosting a fleet of entire Lemmy instances is far more expensive than just small slices of it that may require the additional processing power.
You can easily scale a monolith. You typically horizontally replicate any web server (monolith or not) to handle whatever traffic you’re getting. It shouldn’t really matter what type of traffic it is. Plenty of the world’s biggest websites run monoliths in production. You know how people used to say “rails doesn’t scale”? Well they were wrong because Rails monoliths are behind some huge companies like GitHub and Shopify.
The lemmy backend is also quite lightweight and parallel so it’s cheap and effective to replicate.
In my professional experience microservices are usually a dumpster fire from both the dev perspective and an ops perspective (I’m a Site Reliability Engineer).
Lemmy’s backend is native code, not run in a virtual machine or interpreted from text. You’re not going to pay much extra for an extra megabyte or 10 of RAM being used per instance for the extra code sitting idle. It certainly shouldn’t use much processing power when not in use.
I’d be less concerned with memory (of which Lemmy seems to use very little), and much more concerned with CPU core count. I touched on it in my other comment, but I don’t understand how a few cores is supposed to handle the ridiculous number of federation workers people are setting their instances to.
Does code that exists but isn’t being executed often actually impact CPU usage that much?
Linux kernel has like 30 million lines of code and you probably compile a fifth of it into your actual kernel binary by default. That’s still several million lines, but it doesn’t use much CPU at all. Rather, eliminating all the excess code keeps your size down so you can load it from disk in 0.0001 seconds instead of 0.0002.
Now if code that doesn’t need to run often, runs more often because we scaled the monolith horizontally - that IS a problem, but it’s not a problem inherent to the monolith design pattern, but rather a specific instance of bad design.
What microservices would you split Lemmy into? The database, image hosting and the UI are already separate.
I’d split it out into a few systems
- Signup/Login/Account management
- Posting/Commenting/Voting
- Moderation Controls
- DB Readers and Writers in different services
- Community management (may get lumped into moderation controls, but separation of duties may be needed)
- Edit: Federation is a big one I keep forgetting about
The ultimate goal, and I don’t know how possible it is with rust, would be to have a way to run those as individual services or as one part of a larger monolith. Smaller instances would be able to run it as one binary, while larger instances like Lemmy.world or Lemmy.ml can run each part independently. That would allow easier scaling on large instances while (hopefully) leaving it just as simple to deploy on a small scale too.
There’s no reason to split it into 100 different services, but 4-5 mid sized ones might help.
Well, I’m going to start by repeating that I don’t necessarily agree that it being monolithic is necessarily a problem right now.
The immediate thought in my mind would be all of the federation logic. That’s where all of the instances seem to be lagging behind, and it seems the common fix is “just increase the workers to one billion”. Apparently that does something meaningful, but the developer in me wants to know how a few cores can put so many workers to use.
Spinning federation off into a microservice means you could deploy it on something like Cloud Run or AWS ECS, and have it autoscale as the workload demands it. Seems like a pretty prime candidate to me.
