Is Mastodon's Link-Previewing Overloading Servers ?
The blog Its FOSS has 15,000 followers for its Mastodon account — which they think is causing problems:
When you share a link on Mastodon, a link preview is generated for it, right? With Mastodon being a federated platform (a part of the Fediverse), the request to generate a link preview is not generated by just one Mastodon instance. There are many instances connected to it who also initiate requests for the content almost immediately. And, this "fediverse effect" increases the load on the website's server in a big way.
Sure, some websites may not get overwhelmed with the requests, but Mastodon does generate numerous hits, increasing the load on the server. Especially, if the link reaches a profile with more followers (and a broader network of instances)... We tried it on our Mastodon profile, and every time we shared a link, we were able to successfully make our website unresponsive or slow to load.
It's Foss blog says they found three GitHub issues about the same problem — one from 2017, and two more from 2023. And other blogs also reported the same issue over a year ago — including software developer Michael Nordmeyer and legendary Netscape programmer Jamie Zawinski.
And back in 2022, security engineer Chris Partridge wrote:
[A] single roughly ~3KB POST to Mastodon caused servers to pull a bit of HTML and... an image. In total, 114.7 MB of data was requested from my site in just under five minutes — making for a traffic amplification of 36704:1. [Not counting the image.]
Its Foss reports Mastodon's official position that the issue has been "moved as a milestone for a future 4.4.0 release. As things stand now, the 4.4.0 release could take a year or more (who knows?)."
They also state their opinion that the issue "should have been prioritized for a faster fix... Don't you think as a community-powered, open-source project, it should be possible to attend to a long-standing bug, as serious as this one?"
Abstract credit: https://slashdot.org/story/428030
...and here I am, running a blog that if it gets 15k hits a second, it won't even bat an eye, and I could run it on a potato. Probably because I don't serve hundreds of megabytes of garbage to visitors. (The preview image is also controllable iirc, so just, like, set it to something reasonably sized.)
Wait, you're going to tell me you don't actually have to serve bloat on a blog like it's foss? No way!
I only serve bloat to AI crawlers.
...is a wonderful thing to put in my nginx config. (you can try
curl -Is -H "User-Agent: GPTBot" https://chronicles.mad-scientist.club/robots.txt | grep content-length:to see it in action ;))Your bandwidth bill lol
I don't think serving 86 kilobytes to AI crawlers will make any difference in my bandwidth use :)
Oic its a redirect now
It's not. It just doesn't get enough hits for that 86k to matter. Fun fact: most AI crawlers hit
/robots.txtfirst, they get served a bee movie script, fail to interpret it, and leave, without crawling further. If I'd let them crawl the entire site, that'd result in about two megabytes of traffic. By serving a 86kb file that doesn't pass as robots.txt and has no links, I actually save bandwidth. Not on a single request, but by preventing a hundred others.There's no reason why 114MB of static content over 5 minutes should be an issue for a public facing website. Hell, I probably could serve that and the images with a Raspberry Pi over my home Internet and still have bandwidth to spare.
I think they are throwing stones at the wrong glass house/software stack.
It is not, but a write amplification of 36704:1 is one hell of an exploitable surface.
With that same Raspberry Pi and a single 1gbit connection you could also do 333333 post requests of 3 KB in a single second made on fake accounts with preferably a fake follower on a lot of fediverse instances. That would result in those fediverse servers theoretically requesting 333333 * 114MB = ~38Gigabyte/s. At least for as long as you can keep posting new posts for a few minutes and the servers hosting still have bandwidth. DDosing with a 'botnet' of fediverse servers/accounts made easy!
I'm actually surprised it hasn't been tried yet now that I think about it...
On the other hand, if the site linked would not serve garbage, and would fit like 1Mb like a normal site, then this would be only ~325mb/s, and while that's still high, it's not the end of the world. If it's a site that actually puts effort into being optimized, and a request fits in ~300kb (still a lot, in my book, for what is essentially a preview, with only tiny parts of the actual content loaded), then we're looking at 95mb/s.
If said site puts effort into making their previews reasonable, and serve ~30kb, then that's 9mb/s. It's 3190 in the Year of Our Lady Discord. A potato can serve that.
Foss project: has 100 open issues
A year passes
Foss project: 50 issues got resolved, 50 new ones have been opened in the meantime
Why hasn't this giant project fixed a single bug?
This issue has been noted since mastodon was initially release > 7 years ago. It has also been filed multiple times over the years, indicating that previous small "fixes" for it haven't fully fixed the issue.
Just fucking cache.
If a GET request is breaking your server, you're doing something horribly wrong.
It's about amplification attack. No matter how well you cache, you still will send replies.
Doesn't apply to GET
Next stage: doesn't apply to DNS
For context DNS amplification factor is about 150.
In the comments on the article people have debugged their cloudflare/caching configuration for them and told them what they're doing wrong.
If I understand right that means link previews are requested every single time an user sees it? The instance should request it once a week, cache it and serve that to users
I believe instances generate the preview as soon as it's federated. The problem is that if you have many followers, each of their instances will try to generate a preview at the same time