this post was submitted on 05 Jun 2023
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Lemmy
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Everything about Lemmy; bugs, gripes, praises, and advocacy.
For discussion about the lemmy.ml instance, go to !meta@lemmy.ml.
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The site currently runs on the biggest VPS which is available on OVH. Upgrading further would probably require migrating to a dedicated server, which would mean some downtime. Im not sure if its worth the trouble, anyway the site will go down sooner or later if millions of Reddit users try to join.
π¬
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Maybe some dns fail-over for lemmy.ml to point to join-lemmy.org might be cool indeed π€
Yeah, was thinking of a DNS based solution as well. Probably the easiest and most effective way to do it?
We need Self hosted team and team networking to represent. Would be amazing to see some community support in scaling Lemmy up.
I dont think so, when the site is overloaded then clients cant reach it at all.
It should be compatible if someone sets it up.
You could configure something like a Cloudflare worker to throw up a page directing users elsewhere whenever healthchecks failed.
Then cloudflare would be able to spy on all the traffic so thats not an option.
That's...not how things work. Everyone has their philosophical opinions so I won't attempt to argue the point, but if you want to handle scale and distribution, you're going to have to start thinking differently, otherwise you're going to fail when load starts to really increase.
You could run an interstitial proxy yourself with a little health checking. The server itself doesn't die, just the webapp/db. nginx could be stuck on there (if it's not already there) with a temp redirect if the site is timing out.
How about https://deflect.ca/ they could still spy but probably less bad?
I'm sure you know this, but getting progressively larger servers is not the only way, why not scale horizontally?
I say this as someone with next to no idea how Lemmy works.
Its better to optimize the code so that all instances benefit.
Is it possible to make Lemmy (the system as a whole) able to be compatible with horizontally scaling instances? I don't see why an instance has to be confined to one server, and this would allow for very large instances that can scale to meet demand.
Edit: just seen your other comment https://lemmy.ml/comment/453391
It should be easy once websocket is removed. Sharded postgres and multiple instances of frontend/backend. Though I don't have any experience with this myself.
I think that is unavoidable, Look at the most popular subreddits , they can get something like 80 million upvotes and 66K comments per day, do you think a single server can handle that?
Splitting communities just so that it will be easier technically is not good UX.
@nutomic @Lobstronomosity In one of the comments I thought I saw that the biggest CPU load was due to image resizing.
I think it might be easier to split the image resizer off to its own worker that can run independently on one (or more) external instances. Example: client uses API to get a temporary access token for upload, client uploads to one of many image resizers instead of the main API, image resizer sends output back the main API.
Then your main instance never sees the original image
There is already a docker image so that should not be too hard. I'd be happy to set something up, but (as others have said) the DB will hit a bottleneck relatively quickly.
I like the idea of splitting off the image processing.
Image processing isnt causing any noticable cpu load.
I saw someone say it was, obviously I have no access to data.
Maybe on another instance but not on lemmy.ml
There will either be an hour of downtime to migrate and grow or days of downtime to fizzle.
I love that there's an influx of volunteers, including SQL experts, to mitigate scaling issues for the entire fediverse but those improvements won't be ready in time. Things are overloading already and there's less than a week before things increase 1,000-fold, maybe more.
What's the current bottleneck?
SQL. We desperately need SQL experts. It's been just me for yeRs, and my SQL skills are pretty terrible.
Put the whole DB in RAM :-)
Makes me remember optimization, lots of EXPLAIN and JOIN pain, on my old MySQL multiplayer game server lol. A shame I'm not an expert ...
There are some SQL database optimisations being discussed right now and apparently the picture resizing on upload can be quite CPU heavy.
SQL dev here. Happy to help if you can point me in the direction of said conversation. My expertise is more in ETL processes for building DWs and migrating systems, but maybe I can help?
https://github.com/LemmyNet/lemmy/issues/2877
this seems to be the relevant issue: https://github.com/LemmyNet/lemmy/issues/2877
I've been helping on the SQL github issue. And I think the biggest performance boost would be to separate the application and postgresql onto different servers. Maybe even use a hosted postgresql temporarily, so you can scale the db at the press of a button. The app itself appears to be negligible in terms of requirements (except the picture resizing - which can also be offloaded).
But running a dedicated db on a dedicated server - as close to the bare metal as possible give by far the best performance. And increase it for more connections. Our production database at my data analytics startup runs a postgresql instance on an i9 server with 16 cores, 128GB RAM, and a fast SSD. We have 50 connections set up, and the run pgbouncer to allow up to 500 connections to share those 50. And it seamlessly runs heavy reporting and dashboards for more than 500 business customers with billions of rows of data. And costs us less than US$200pm at https://www.tailormadeservers.com/.
This suggestion probably won't help with hosted VPS, but lib nvJPEG pushes crazy theoretical numbers for image resizing.
Maybe this could be worth investigating?
Probably not, but it does mention a more general CUDA based solution that might be interesting to add to Pictrs. I could for example move my Pictrs instance onto a server that does have an older Nvidia GPU to accelerate stuff (to use for Libretranslate and some other less demanding ML stuff).
Edit: Ok looks like the resizing is anyways only supported on Pictrs 0.4.x which most Lemmy instances are not using yet. However this seems to use regular ImageMagick in the background, so chances are quite high that it can be made to work with OpenCL: https://imagemagick.org/script/opencl.php
And may be the bandwidth. Serve thousands and thousands need at minimum 1gbps.
Its mostly text so bandwidth shouldnt be a problem.
Is it running in a single docker container or is it spread out across multiple containers? Maybe with
docker-machineor kubernetes with horizontal scaling, it could absorb users without issue - well, except maybe cost. OVH has managed kubernetes.So reading this correctly, it's currently a hosting bill of 30 Euro a month?
No, thats the 8 GB memory option... if its the biggest, it should be around 112 β¬.
Its the one for 30 euros, Im not seeing any vps for 112. Maybe thats a different type of vps?
in vservers, it depends on the memory β¦ and storage option for the one starting at 30β¦
It currently has 8gb and only uses 6gb or so. CPU is the only limitation.
It does not sound like OVHs vServers offer dedicated cores, and it is common to quickly become a bottleneck with VPS offerings across hosters and for example with the initial Mastodon hypes, i had to learn that shared hardware lesson the hard way. For the price you are currently paying, maybe something like a used dedicated (or one of the fancy AMD ones) server at Hetzner is of interest: https://www.hetzner.com/sb
Hetzner is great but they are very strict about piracy, so its not an option for lemmy.ml. For now the load has gone down so I will leave it like this, but a dedicated OVH server might be an option if load increases again.
You should use this relatively quiet time to migrate to a larger server, because when the time comes where you need to do it, you're going to be in for a world of hurt. This is the calm before the storm--take advantage of it.
Ultimately, you need to scale horizontally. You need to shard your database and separate out your different functions (database, front end, whatever back end applications you use, etc) onto different servers, all fronted by load balancers. That's going to be the only way to even begin to handle increasing load. If you don't have a small team of experienced engineers with a deep understanding of how to build for scale, and you get a sudden mass exodus of users from Reddit, you're fucked. So if I were you, here's what I'd do:
Scale up to the largest instance type you can. If possible, switch (at least temporarily) to AWS and use something in the c6i instance family, such as the c6id.32xlarge. Billing for AWS instances is done by the hour, so you wouldn't need to pay for an entire month up front if you only need that extra horsepower for a few days (such as when the blackouts are planned from the 12th through 14th).
Because the above will do nothing but buy you time until you crash--and if you get a huge spike of users, without horizontal scaling, you WILL crash--migrate your DNS to something like Cloudflare. From there, configure workers to respond when health checks to your site fail, so that users attempting to access the site can be shown a static page directing them to something like http://join-lemmy.org or someplace, instead of simply getting 5xx errors.
Once the hug of death is over, evaluate where you stand. Reduce your instance size, if you can, and start investigating what it's going to take to scale horizontally.
I'm not a SQL expert, but I am a principal network architect, and my day job for the last 15 years has been working on scale and automation for the world's largest companies, including 7 years spent at AWS. In my world, websites like Reddit, as large as they are, are still considered to be of 'average' size. I can't help you with database, but I'm happy to provide guidance around networking, DNS, scale, automation, security, etc.
I believe @ernest is just about to do a backend re-factor on https://kbin.social/ if you had the time and inclination a ticket here outlining some optimisations for horizontal scaling might be timely https://codeberg.org/Kbin/kbin-core
I'm relatively new to https://elest.io/pricing but it seems an easy way to scale stuff up (and down again) Dockerised, just upgrade the plan to the next tier when needed. Pay by the hour. Downgrade it again later.
There's also a bunch of load balancer options I haven't even begun to explore yet.
If you select Hetzner it's EU based & powered by green energgy
Yeah, the biggest seems to be β¬110 per month if they donΒ΄t get a discount for committing to a longer contract duration.
Really ?
Do you have the frontend a DB serving in the same VPS? If so it would be a great time to split them. Likewise if you DB is running in a VPS, you're likely suffering from significant steal from the hypervisor so you would benefit from switching to a dedicated box. My API calls saw a speedup of 10x just from switching from a VPS DB to a Dedicated Box DB.
I just checked OVH VPS offers and they're shit! Even at 70 Eur dedicated on hetzner, you would gain more than double those resources without steal. I would recommend switching your DB ASAP for immediate massive gains.
If you're wondering why you should listen to me, I built and run https://aihorde.net and are handling about 5K concurrent connections currently.