Direct link to article:
https://news.itsfoss.com/mastodon-link-problem/
TL;DR:
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.
Does Lemmy not cause this issue? Other federated software was not mentioned in the article at all.
So the preview should be federated as well?
How many requests are we actually talking about here, though? Is that better or worse than everyone clicking the link?
There’s some problem with a federated previews: tricking one instance into generating the wrong preview would spread to every instance. It’s been exploited for malware and scam campaigns in message apps.
Here’s a related, interesting example for BlueSky, on generating disguised links and preview cards (with content the url doesn’t actually contain) for anyone curious: https://github.com/qwell/bsky-exploits
Lemmy (and Kbin for that matter) very much do the same thing for posts. I don’t think they fetch URL previews for links in comments, but that doesn’t matter: posts and comments are both fairly likely to end up spreading to Mastodon/etc anyway, so even comments will trigger this cascade.
Direct example: If you go to mastodon.social, stick @fediverse@lemmy.world in the search box at the topleft and click for the profile, you can end up browsing a large Mastodon server’s view of this community, and your very link has a preview. (Unfortunately, links to federated communities just result in a redirect, so you have to navigate through Mastodon’s UI.)
Real talk, the mastodon traffic stampede isn’t that bad for a properly configured website.
Just put the site behind a cache, like Cloudflare, and set your cache control headers properly?
They mention that they are already using Cloudflare. I’m confused about what is actually causing the load. They don’t mention any technical details, but it does kinda sound like their cache control headers are not set properly. I’m too lazy to check for myself though…
I’ve found that if left on default settings, CloudFlare is not that great at caching. It requires a bit of configuration to really make it sing. itsfoss.com thought they were “using CloudFlare” but probably not to it’s fullest potential.
Even without Cloudflare, simple NGINX microcaching would help a ton there.
It’s a blog, it doesn’t need to regenerate a new page every single time for anonymous users. There’s no reason it shouldn’t be able to sustain 20k requests per second on a single server. Even a one second cache on the backend for anonymous users would help a ton there.
They have Cloudflare in front, the site should be up with the server being turned off entirely.
I’m confused about what is actually causing the load.
Thousands of instances simultaneously fetching link previews from a VPS w/2GB RAM.
This should be front and center, caching won’t be able to make up for that…
It’s an interesting and frustrating problem. I think there are three potential ways forward, but they’re both flawed:
-
Quasi-Centralization: a project like Mastodon or a vetted Non-Profit entity operates a high-concurrency server whose sole purpose is to cache link metadata and Images. Servers initially pull preview data from that, instead of the direct page.
-
We find a way to do this in some zero-trust peer-to-peer way, where multiple servers compare their copies of the same data. Whatever doesn’t match ends up not being used.
-
Servers cache link metadata and previews locally with a minimal amount of requests; any boost or reshare only reflects a proxied local preview of that link. Instead of doing this on a per-view or per-user basis, it’s simply per-instance.
I honestly think the third option might be the least destructive, even if it’s not as efficient as it could be.
Or 4) Ignore noise and do nothing; this is a case of user talking about things they don’t understand at best, or a blog intentionally misleading others to drum up traffic for themselves at worst. This is literally not a problem. Serving that kind of traffic can be done on a single server without any CDN and they’ve got a CDN already.
That sounds a lot like a weird spin on the Slashdot effect, caused by content mirroring. It seems that it could be handled by tweaking the ActivityPub protocol to have one instance requesting to generate a link preview, and the other instances copying the link preview instead of sending their own requests.
But frankly? I think that the current way that ActivityPub works is outright silly. Here’s what it does currently:
- User is registered to instance A
- Since A federates with B, A mirrors content from B into A
- The backend is either specific to instance A (the site) or configured to use instance A (for a phone program)
- When the user interacts with content from B, actually it’s the mirrored version of content from B that is hosted in A
In my opinion a better approach would be:
- User is registered to instance A
- Since A federates with B, B accepts login credentials from A
- The backend is instance-agnostic, so it’s able to pull/send content from/to multiple instances at the same time
- When the user interacts with content from B, the backend retrieves content from B, and uses the user’s A credentials to send content to B
Note that the second way would not create this “automated Slashdot effect” - only A would be pulling info from the site, and then users (regardless of their instance) would pull it from A.
Now, here’s my question: why does the ActivityPub work like in that first way, instead of this second one?
If server A makes one request, it keeps server B from being overload by thousands of requests from users A.
“A” Users would need to send requests to some server anyway, either A or B; that’s only diverting the load from B to A, but it isn’t alleviating or even sharing it.
Another issue with the current way that ActivityPub works is foul content, that needs to be removed. Remember when some muppet posted CP in LW?
Yes, but this way demand on instances scales with user count and aliows smaller instances to exist. Otherwise an errant toot on a small instance that suddenly gets popular will instantly drag that smaller instance down.
Check out Nostr, ActivityPub alternative that does authentication separately from content, works more like that.
