I’ve recently been wondering if Lemmy should switch out NGINX for Caddy, while I hadn’t had experience with Caddy it looks like a great & fast alternative, What do you all think?
EDIT: I meant beehaw not Lemmy as a whole
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The problems I see with Lemmy performance all point to SQL being poorly optimized. In particular, federation is doing database inserts of new content from other servers - and many servers can be incoming at the same time with their new postings, comments, votes. Priority is not given to interactive webapp/API users.
Using a SQL database for a backend of a website with unique data all over the place is very tricky. You have to be really program the app to avoid touching the database and create queues and such when you can. Reddit (at lest 9 years ago when they open sourced it) is also based on PostgreSQL - and you will see they do not do live inserts into comments like Lemmy does - they queue them using something other than the main database then insert them in batch.
email MTA apps I’ve seen do the same thing, they queue files to disk before putting into the main database.
I don’t think nginx is the problem, the bottleneck is the backend of the backend, PostgreSQL doing all that I/O and record locking.
Hm, that’s an interesting take. To be quite honest I saw issues with diesel-rs in production on another website I was contributing too, maybe it’s the issue?
I doubt it is anything that level. The problem is the data itself, in the datababase.
A reddit-like website is like email, every load from the database has unique content. You really have to be very careful when designing for scalability when almost all the data is unique. Especially in modern times where users block other users, and even 2 people loading the same posting do not get the same comments. It’s anti-cache, and you have to really work hard to design that to run efficiently on small servers.
As opposed to a website like Amazon where the listing for a toothbrush is not unique on every page load. There aren’t new comments and new votes altering the toothbrush listing every time a user refreshes the page. And people aren’t switching brands of toothbrush every 24 hours like the front page of Reddit abandons old data and starts with fresh data.
Would a good solution be to just deffer changes to data with something like Apache Kafka? Or changing to something that can be scaled, like cockroach db or neondb? I also heard ScyllaDB could be a great alternative, mostly from reading the discord technical blog.
It’s not the tech here. Postgres can scale both vertically and horizontally (yes there are others that can scale easier or in different factors of CAP).
The problem is how the data is being stored and accessed. Lemmy is doing some really inefficient data access and it’s causing bottlenecks under load.
Lemmy (unfortunately) just wasn’t ready for this level of primetime yet… It has a number of issues that are going to be quite tricky to fix now that it’s seen such wide adoption (database migrations are tricky on their own, doing so on a production site even harder, doing so on 8k+ independent production sites… Sounds like a nightmare)
Can you elaborate on what Lemmy is doing that’s inefficient? I’m working on a database application myself, so the more I know about optimizing database queries, the better.
Sorry, I assumed it was just an issue with the tech not scaling well, really shows how little I know about architecture haha.
something like Apache Kafka
Not that I see. A database like PostgreSQL can work, but you have to be really careful how new data flows into the database. As writing to the database involves record locking and invalidates the cache for output.
Or changing to something that can be scaled, like cockroach db or neondb?
Taking the bulk data, comments and postings, outside PostgreSQL would help. Especially since what most people are reading on a Reddit-like website is content form the last 48 hours… and your caching potential dies way down as people move on to the newer content.
The comments alone are the primary problem, there are lot of them on each posting and they are bulky data. Also comments are unique data.
hmmm a good approach would be to maybe split comments into some kind of database regions and just load as they’re needed instead of loading them all at once
nginx is like, the gold standard. it’s performant as heck. the issues are likely a culmination of many small sub-optimal pieces.
That’s why I think Caddy should be considered, as it has less moving parts, therefore less suboptimal pieces.
One more thing I forgot to mention. The nginx 500 errors people are getting on multiple Lemmy sites could improve shortly with the release of 0.18 that stops using websockets. Right now Lemmy webapp is passing those through nginx for every web browser client.
ohgod
From what I’ve read, the 500 errors are caused by nginx’s failure mode of
“Fuck it, I’m dropping this connection”
Caddy seems to want to keep connections going even if it has to slow down.
Here is a caddy vs nginx benchmark test. A lot to read, but gives an idea where the strengths of both are and where not.
https://blog.tjll.net/reverse-proxy-hot-dog-eating-contest-caddy-vs-nginx/
Huh, that’s interesting, thank you for linking it!
People comment a lot on performance, but I think Caddy can (and should) hold up perfectly fine. It might be worth it to experiment with running servers half on Caddy and half on NGINX, then see how the traffic is being handled by both to compare.
I do think the much cleaner config makes up for the maybe slight performance loss, though. It’s just so much less work to set up and maintain compared to NGINX. The last time I’ve used NGINX was years ago, when I decided to drop it entirely in favor of Caddy. I do think NGINX is only “standard” because it came before Caddy, and that most applications should not prefer it over Caddy.
I, too, dislike NGINX configs, but mainly I think Caddy should be considered for the feature set and performance it has over nginx. While it is true that nginx is pretty performant, that is without talking about third party modules written in Lua. Cloudflare had an amazing post about it a while back where they said while nginx on its own is ok, when you add third party scripts into the mix it slows down to a craw.
I had no idea that NGINX has Lua plugins. You’d probably want to check if Caddy has equivalents for those plugins though, or just implement them in Go yourself.
Caddy uses go based plugins, I remember, they’re called modules.
Source: https://caddyserver.com/docs/modules/ & https://caddyserver.com/docs/extending-caddy
Why is nginx preferred over Apache these days? I believe nginx was originally preferred because Apache had scaling issues with its original forking concurrency model, but that was replaced a long time ago, so…why use nginx today?
That’s why I’m entertaining the idea of an alternative in this post. Although it seems there are a lot of mixed opinions on this matter
Is lemmy copled to a specific web server? Can’t you use whatever you want?
The default seems to be NGINX for all the instances however
I don’t know about Caddy, but if they aren’t using Varnish or similar they should consider it. A caching server can be helpful for frequently repeating fairly stable parts of websites and has a fairly significant performance benefit.
I think considering alternatives is important. Even if the ‘default’ option is good enough. I always enjoy looking around for new ways to go about things.
