My pals in BBC World Service have been doing some awesome work on "lite" versions of their news articles (other page types to follow).
They essentially skip the Server-Side React hydration which means you end up with a simpler HTML+CSS page, no JS.
Page sizes drop significantly:
Fediverse traffic is pretty bursty and sometimes there will be a large backlog of Activities to send to your server, each of which involves a POST. This can hammer your instance and overwhelm the backend’s ability to keep up. Nginx provides a rate-limiting function which can accept POSTs at full speed and proxy them slowly through to your backend at whatever rate you specify.
For example, PieFed has a backend which listens on port 5000. Nginx listens on port 443 for POSTs from outside and sends them through to port 5000:
upstream app_server { server 127.0.0.1:5000 fail_timeout=0;}
This will use up to 100 MB of RAM as a buffer and limit POSTs to 10 per second, per IP address. Adjust as needed. If the sender is using multiple IP addresses the rate limit will not be as effective. Put this directive outside your server {} block.
Then after our first location / {} block, add a second one that is a copy of the first except with one additional line (and change it to apply to location /inbox or whatever the inbox URL is for your instance):
300 is the maximum number of POSTs it will have in the queue. You can use limit_req_dry_run to test the rate limiting without actually doing any limiting – watch the nginx logs for messages while doing a dry run.
It’s been a while since I set this up so please let me know if I mixed anything crucial out or said something misleading.
For a very small instance with only a couple of concurrent users a CDN might not make much difference. But if you take a look at your web server logs you’ll quickly notice that every post / like / vote triggers a storm of requests from other instances to yours, looking up lots of different things. It’s easy to imagine how quickly this would overwhelm an instance once it gets even a little busy.
One of the first web performance tools people reach for is to use a CDN, like Cloudflare. But how much difference will it make? In this video I show you my web server logs before and after and compare them.
The short answer is – before CDN: 720 requests. After CDN: 100 requests.
Usually just turning on a CDN with default settings will not help very much, you’ll need to configure some caching rules or settings. By watching your server logs for a while you’ll get a sense for what needs to be cached but check out mine for a starting point:
Beware of caching by URI Path because often fediverse software will return different data depending on the Accept header that the requester sets. For example, on PieFed and Lemmy instances a request by a web browser to /post/123 will return HTML to show the post to someone. But when that same URL is requested with the Accept: application/ld+json header set, the response will be an ActivityPub representation of the post! You don’t want people getting activitypub data in their browser and you don’t want to be serving HTML to other instances. Once you spot a URL you want to cache, use a tool like Postman to set the Accept header and make a fake ActivityPub request to your instance and see if you get back HTML or JSON.
Another problem that can happen is that often a response will vary depending on whether the viewer is logged in, or who is logged in. If you can figure out how to configure the CDN to pay attention to cookies or whatever headers are used for Authentication by your platform then you might be able to cache things like /post/*… I couldn’t.
The things I’ve chosen to cache by URI Path above are ones that I know don’t vary by HTTP header or by authentication.
Although we can’t use URI Path a lot of the time, we can cache ActivityPub requests by detecting the Accept: allocation/ld+json header:
https://join.piefed.social/wp-content/uploads/2024/02/caching_activity2-1024x811.pngThis will cache all ActivityPub requests, regardless of URL. People browsing the same URLs as those used by ActivityPub will be unaffected as their requests won’t have the special HTTP header. I used a short TTL to avoid serving stale data when someone quickly edits a post straight after creating it.
There seems to be a deep vein of optimization here which I’ve only just started to dig into. These changes have made a huge difference already and for now my instance is under very little load so I’ll leave things as they are. I look forward to learning more about this in future.
Google provides a tool called PageSpeed Insights which gives a website some metrics to assess how well it is put together and how fast it loads. There are a lot of technical details but in general green scores are good, orange not great and red is bad.
I tried to ensure the tests were similar for each platform by choosing a page that shows a list of posts, like https://mastodon.social/explore.
The rest don’t seem to have prioritized performance or chose a software architecture that cannot be made to perform well on these metrics. It will be very interesting to see how that affects the cost of running large instances and the longevity of the platforms. Time will tell.