Is the app stack naturally resource heavy or is this setup particular different to how a instance should be?
1. Those 30k users who are following users on other servers, which pulls in the content of those users. I'm on hachyderm but I would guess only about 20% of the people I follow are. That means my user is pulling in 250 other users data into the system. Of course most, if not all, of the people are follow are being followed by someone else so it's not a pure multiplier. At the same time it does mean it's a lot more data moving in.
2. NFS, which is where they had the problems, was being used as a media store. People on mastodon and twitter like sharing images and other media. Even people who run single user nodes but follow a lot of people end up using a ton of storage space. 30k people scrolling through timelines and actively pulling that data out, while queues are pushing data in, can be tough to scale. Switching to an object store really helped fix that.
On top of that the mastodon app is very very sidekiq heavy. For those not familiar with ruby, sidekiq is basically a queue workload system (similar to python's celery). You scale up by having more queue workers running. The problem with NFS is that all of those queues are sharing the filesystem, making the filesystem a point of failure and scaling pain. Adding more queue workers makes the problem worse by adding to the filesystem load, rather than resolving the problems. Switching to an object store helps until the next centralized service (in this case postgres) reaches its limits.
So basically the 30k users each following their own set of users creates a multiplier on how many users the instance is actually working with. The more users on either side of the equation the more work that needs to be done. If this was a 30k user forum where every user existed on the instance the load would be significantly less.
It is not NFS that is a SPOF, it is a single NFS server that is a SPOF. There exists distributed NFS systems (OneFS, Panasas) that can tolerate the loss of up to N servers before the service gets disrupted.
No more I/O to be had from that particular NFS server. If your mounts are distributed over 4+ servers, then you have potentially 4x the available operations available.
the main problem was slow io because of faulty disks which brought everything to a crawl.
Imagine your subscriptions and account living on one server, then when you log in that server gives you the list and your client goes and gets all the data.
We already had this sort of federation figured out, it's the open web. We just have to find a way to get the open web to provide the things that google, facebook, reddit, provided.
Easy way to contribute content.
Discovery for new content.
Search ability.
Kill the things centralized websites provided, let people host websites within that system, and let the clients handle dealing with the fact that there are all sorts of providers out there.
That would suck on a mobile device with limited bandwidth and/or data. Also lots of repetitive fetching when people have large number of followers too, no?
Why would it be any different than using a mobile feed reader to follow hundreds of blogs, or using a podcast app to follow hundreds of podcasts? Both are commonly done on mobile all the time. Checking if a feed has been modified since the last time the client checked costs virtually nothing.
bioemerl: I've been casually digging into Mastodon and ActivityPub for the last few weeks and FWIW I think you're absolutely right — with the caveat that I may be missing something obvious, it's seems very dumb for Mastodon/ActivityPub servers to be downloading and delivering content on behalf of client apps.
In my experience, you generally do that through an aggregator which has already cached the articles for you and you're doing a bulk fetch from a single host - that is quite different to calling out to hundreds of individual hosts and fetching a page from each.
> it's seems very dumb for Mastodon/ActivityPub servers to be downloading and delivering content on behalf of client apps.
Isn't that literally what an RSS aggregator does?
My understanding is that a cloud-based aggregator (like Feedly) delivers feed and state information to clients, but not the content itself.
To test this with blogs, I did a new install of Reeder, synced with Feedly, then turned off Wi-Fi. In my subscriptions, I got everything that would be in the feeds themselves (notably item titles and descriptions as created by publishers) but nothing beyond that. The offline experience was mostly useless, suggesting that the client does most of the heavy-lifting even when leveraging cloud-based aggregators.
So is making a few REST API calls a significant savings over checking a couple hundred (or whatever) RSS feeds? With "If-Modified-Since" checks being so cheap, I'm not sure that inserting Mastodon instances as middleboxen makes sense. If all Mastodon did was store subscriptions and state info, it seems like we'd have a far more resilient microblogging ecosystem.
Depends entirely on the feed. Just checked my most recent 100 entries from Feedbin - that comes back with 23k of `summary` and 508k of `content`. That was one call to return 661k of JSON covering 28 feeds.
> So is making a few REST API calls a significant savings over checking a couple hundred (or whatever) RSS feeds?
I've made one call to get (assuming >2k in `content` is a full article) 74 full articles from 28 feeds. Add another 26 and I'm looking at 27 total.
Even just retrieving the RSS feeds is 28 and 26 more for the non-included articles to make a total of 54 - double what I had to do via Feedbin. That's before we start considering response times and latency for each of those sites which would drag things down even further.
There's a reason why people use RSS aggregators!
It would be akin to having single-user mastodon instance
It's great for reading from lots of new sites at the same time, but it's clear that it hasn't taken off and when that happens it's normally for pretty good reason
As in you can subscribe to who you want and no moderator will stop you and then you can... just comment on a blogpost or article, with no 3rd party aside from this particular space moderators
Wasn't it solved by moving to RSS aggregators and doing a single bulk fetch of your cached N blogs rather than calling out individually to N blogs?
Would be interesting seeing Twitters complete backend and while mastodon might not be apples to apples also interested cost per user to infrastructure analysis too.
I have no love for Rails, but blaming it for Twitters old problems is not fair.
That said, Mastodon has much of the same problem, and is only "saved" by the combination of federation and ten years of hardware advances. Thankfully, the federation means there's plenty of opportunity for people to experiment with other implementations of ActivityPub (or even implementations of the full Mastodon API), or fixes to it.
I dread to think how much a busy 30k user instance does.
Sure ... but that's not what I was talking about. It's still talking ActivityPub and that seems, to me, from my low use, few user instance, to be an extremely chatty protocol. I don't know if the ActivityPub traffic scales linearly with users but it would be a not inconsiderable number for 30k users.
[1] https://the-federation.info/pleroma [2] https://instances.social