Correct me if I’m wrong. I read ActivityPub standards and dug a little into lemmy sources to understand how federation works. And I’m a bit disappointed. Every server just has a cache and the ability to fetch something from another known server. So if you start your own instance, there is no profit for the whole network until you have a significant piece of auditory (e.g. private instances or servers with no users). Are there any “balancers” to utilize these empty instances? Should we promote (or create in the first place) a way how to passively help lemmy with such fast growth?
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You are right. On the one hand, it’s kind of bad, naive distributed architecture (my day job), it could have been done much better. On the other hand, the more important point is that it demonstrates an alternative to centralized. We’ll learn a lot about usage patterns here, get new ideas, and either improve Lemmy or build something better from the ground up. Big thanks to Reddit for driving users this way to test scalability and get much better knowledge of usage.
It’s not distributed architecture as you normally think it - it’s a decentralised federation. It’s an important distinction from your typical distributed architecture app.
Can you explain what’s the difference?
A distributed architecture generally refers to a single application or service designed to be resilient to individual data center failures. For example, Reddit, a centralized application controlled by Reddit itself, operates data centers around the world to process user transactions. In the event of an outage in a specific location, such as California, Reddit would still be able to function because its infrastructure for handling user requests and serving data would automatically switch to other functioning data centers elsewhere, like Nevada, Arizona, or Washington. This is an example of a distributed architecture.
On the other hand, a decentralized federation does not consist of a single application. Instead, it involves a software platform like Lemmy, which is hosted on multiple individual hosts. When a user signs up with one host, they can interact with users from other hosts, but each host manages its own infrastructure. For instance, someone could host a Lemmy instance on an old laptop they found in their closet and name it ballsuckers.com, while another person could host a Lemmy instance in the cloud with a properly designed distributed architecture and name it bingbong.com. Each host is responsible for managing its own instance. Users from both instances can interact with each other, but if, for example, the hard drive of ballsuckers.com were to fail, the entire ballsuckers.com instance would go down. However, this would not affect bingbong.com because its infrastructure is separate and managed independently.
I hope this helps!
it could have been done much better.
Care to expand on this point?
Disclaimer: I’ve only looked a bit at the protocols and high levels descriptions of how it works, and this is just my understanding of it. But it seems to track.
let’s take … [email protected] for example. Right now lemmy.world is the Source of Truth on this, which means if you sign up for it on a different host, let’s say myawersomeinstance.com, that first contacts lemmy.world, copies over posts, and then subscribes on new posts for that. Actually not 100% sure if lemmy.world contacts myawersomeinstance.com when there’s a new post, or myawersomeinstance.com polls lemmy.world… But anyway, point is, lemmy.world is authority on it. myawersomeinstance.com also have [email protected] data, but it’s a copy of it. And lemmy.world is only authority. So if you post something, your server then sends it to lemmy.world and waits a reply. Then lemmy.world contacts all instances that has at least one user following this to tell about the new post. And that new post now exists on a few hundred databases.
The problem is the scaling is whack. Okay, you can have 5000 federated servers with users subscribing to [email protected], but that means lemmy.world needs to update 5000 servers per post, and there’ll be 5000x storage used for that post, and ALL 5000 servers contacts lemmy.world to get the new good stuff.
Frankly, it’s a scaling nightmare. As for a different approach, you could have private / public keys and sign updates from lemmy.world and allow the other instances to fetch the new data from each other. That would also allow more relaxed caching, since it would be generally lower cost to re-fetch the data. Now you need aggressive caching because you don’t want lemmy.world to keel over and die form every server on the planet wanting to hear the latest and greatest posts all the time.
Thanks for the in depth write up! I haven’t looked too far into the docs or the subscription model, but is this a fault on Lemmy’s end, or is this a function of how activity pub handles federated communication? (I’m very new to activity pub/federation, just now reading through the activity pub docs)
I do like your idea of distributed replication via keys,much better than what I had brainstormed
Edit: yeah it does look like it’s a function of activity pub, wonder if theres a more scalable federation protocol out there
Could lemmy.world put a load balancer in front and use that to direct requests to different instances of lemmy.world? Not sure if that question is dumb I’m not a technical guy.
It’s not dumb at all, and it’s a common scaling technique. But the software needs to support it, and I have no idea if lemmy has support for running multiple instances for one server.
What makes a distributed system good that Lemmy hasn’t done? Seems like a pretty robust system to me, seems like scaling issues are on the instance host themself. With Reddit’s experience, I don’t see how there are issues
If there was an easy solution that balanced decent UX and performance, we’d have it by now!
I just commented on this in another thread: https://lemmy.world/comment/76011
TL;DR: The server-to-client interactions on Lemmy are a lot heavier than the server-to-server interactions, so even if you’re just using your own server to interact with communities on other servers, it should still take load off of the servers you would have been using directly.
That’s news to me. I thought serverto-server interactions would be heavier since other instances will keep fetching contents from your instance once they start federating. I guess it’s better to join less populated instances instead of crowding on a single instance.
I’ve created my own instance in order to not create more load on others and it took a minute to realise I needed to populate it myself, would be nice to have a default view aggregating popular posts etc. across instances. But maybe I’m just asking for too much hehe
That’s an interesting idea. Maybe you could even choose the “default subs” for your instance from across lemmy.
I did the exact same thing. Ended up looking up the more popular communities on the bigger instances and searched for them on mine to index them.
I wish there was an easier way, but for now there isn’t.
I’m quite worried of how well this federation system will work in the long run, especially when more people coming from Rexxit. As people make more post/comments, every federated instance will have to cache more redundant contents from each other, which also will use more storage thus increasing the fee of every instance hoster. There’s also another problem of visibility in search engines. Because Lemmy/Kbin can be hosted by anyone, it makes searching on a specific domain impossible, unlike how I can just add “reddit” in the search query. Also since there are multiple Lemmy/Kbin instances, there’s a chance there’ll be similar communities spread over, fragmenting the communities even further. Until they can find a way to fix those problem, I don’t think federation is suited for large scale communities.
As for fragmentation problem, maybe adding a global search for communities like this will help reducing fragmentation. Users can still make their own community in their instance, while other people who don’t need to can easily find the community they want.
A network of (“thousands of”) servers has — like most things — pros and cons.
Some of the pros are:
- The network is more resiliant against outages. If lemmy.ml is down, all other users can still access the network.
- It’s hard to take legal action against the network or to buy it out (like Big Players™ like to do to get rid of potential competitors).
- It allows various similar or even conflicting moderation policies. The network, i.e. the infrastructure doesn’t allow or prohibit any specific opinion (the communities do).
- It allows for different ways to pay the bills: goodwill of the admin, donaitions, ads, fee or selfhosting. The latter also allows great control over the data so you control your privacy.
Some of the cons are:
- Content is replicated across servers, which increases the total amount of data stored.
- Latency and speed suffer.
- Interoperability with the wider Fediverse is less than 100%, which can create confusion and frustration.
- Discovery is more difficult.
This has definitely been a problem with communities being created on the bigger instances and not utilising smaller instances. Happy for someone to say I’m wrong etc, but I think there would be merit in capping instances to x number of users or communities, to force the user base to spread out.
Also, the way signups work, (ie you find a community you like then click sign up but that signs you up to that instance), further exacerbates the issue and the confusion around how federation works. The sign up links on each instance should lead either to a page with an instance finder, or to a random instance that matches the profile of, and is already federated with, the instance you were on. Otherwise the larger instances have a monopoly and are just going to lead to a bad user experience when they can’t cope with the traffic.
It’s a self defeating prophecy if users only want to sign up to the instances with the big communities, because then everyone is going to keep creating communities there and nobody is going to want to join a smaller instance.
I might be talking nonsense and am happy to be told why that is all wrong :)
Yes, there should be instance caps, and they should be visible to users.
That way users can scale, choose, without much thinking.
This same techinque works everywhere, for example MMO games. You have availability visible and choose servers according to it.
This would fix scaling partially without much technical changes.
Based on the bit of research I have done, along with creating https://lemmyonline.com/
It seems you are correct. A small handful of servers contains roughly 95% of the user-base.
I think the intended way for this to work, certain communities can be hosted on their own servers. However, it appears most of the popular communities migrating away from reddit, all flocked to lemmy.world, which is likely contributing to it being overloaded.
Are all these thousands of lemmy servers useless?
almost. It’s actually worse than that - when you subscribe to a community from your server it will fetch like 20 posts and that’s it, you’ll get only new stuff after that, so there’s no possibility to do a full mirror of selfhosted, for example, if you started your instance today and didn’t fetch posts and comments manually.
ActivityPub per se is just a spec on s2s/s2c communication, which is not a great thing since in many cases it assumes single source of truth, which potentially puts huge load on more popular instances.
I think a quick and dirty hack to this could be the following - each linked instance may maintain cache of announces (so there would be benefit of just forwarding original http signed requests w/o being afraid of malicious actor), which your instance could pull, this way you could populate your mirror without overloading the original source.
Distributed activities propagation though… Let’s say there are some design steps involved to make this truly distributed, however I feel like it’s possible.What’s the alternative? You go full-banana decentralised or mega-site Reddit. I think Lemmy is a nice middle ground
Proper data model would be a start, i.e. public-key based identities instead of just the old name@server. That way you could hop from server to server and still be the same account. Would make the whole thing a hell of a lot more robust, as in case of server failure could just continue as if nothing happened on another server.
I just spun up my own instance as well and it does feel a bit like I’m just pulling from the biggest instances and feeding my own without really being able to give much back.
You’re reducing load on the bigger instances by not using them directly, which is giving something back
Since Lemmy instance are not backed by commercial interest, but rather by nice volunteers and donors that have money and time to spare, they will be heavily affected by economic downturns (we still can see commercial interests still affect users negatively tho with reddit). Here are my thoughts on the matter:
- as far as I understand the owner of the domain: https://lemmy.world even has to pay for this fancy domain name in the DNS system … every month subscription service style
- (and tbh I hate the Domain name system) why should I fund it with my own money?
- if you hosted with an onion site over tor that expenditure would not exist, but how would users discover your site then? Let me know if you know something about this
- in times of deflation (meaning money becomes worth more, spending some money on a self hosted lemmy instance becomes nonsensical)
- tbh if I hosted a lemmy instance and the users of my instance posted high quality content in quantity I would use it to train my own LLM, that would at least create some economic incentive for me to host such a page … but managing spam and bots will be HARD
That is why you should always back up your comments on your personal device, would be nice if lemmy had an automated way of doing this (I should look into this more)
Domain names are cheap, like $25/year.
- as far as I understand the owner of the domain: https://lemmy.world even has to pay for this fancy domain name in the DNS system … every month subscription service style
I’ve suggested a routing protocol to the lemmy devs - to use federated instances to route all the messages to other federated instances. The idea was received with some interest, but it seems that people believe that there’s still a ton of performance that can be squeezed out from the current architecture through optimisations.
I have my own Lemmy instance running on my home server, but I’m here. “But Bizzle,” you may be asking yourself, “why go through all the trouble of configuring your own instance just to wind up on Lemmy.World anyway?”
I’m glad you asked! And the answer is that federation only fetches parent comments. I’m glad Lemmy exists, and I’m going to keep using it, but we need federated sibling comments for this to actually be good, in my opinion.
EDIT: I actually couldn’t have been more wrong.
I’m not sure I understand what you’re saying. Did you mean that child comments are not federated?
I don’t think that’s correct.
I would be happy if my locally posted comment showed up on lemmy.world at all :-) (If this one does, maybe I was just impatient with the initial sync or so)
EDIT: Nevermind, I was too impatient :-)
Every server just has a cache … there is no profit for the whole network …
I wouldn’t say that caching is no profit. Yesterday there were several times when lemmy.ml was struggling or effectively down for some people, but despite complaints over there I could read lemmy.ml communities just fine through my instance. Caching meant that I was isolated from the service interruption, and the lemmy.ml server was isolated from my contribution to its load.
As I said, there is no profit from empty instances. Of course, the federation itself is good and fail-proof in this way. But if nobody asks for this cache, it’s just an Internet Archive of a sort.
It only takes one user for an instance to not be empty. Every bit of decentralisation adds resilience to the whole. But more decentralisation adds more resilience, so let’s try to spread out the communities and users.
Lemmy is very similar to Matrix. By the way, there are channels in Matrix. There are communities on Telegram…
