- Making assets embedded as base64 (img src the header logo as base64, all CSS should be inline, etc.).
- Leveraging CSS as much as possible (if you use animations and transitions, use CSS as much as possible for these, avoid JS for them).
- Make sure your website is mostly rendered on the backend. If you're to have JS, your website should work without it.
- Security becomes REALLY fun, as in, avoid XSS, CSRF, SQL Injection attacks and any other injections as much as possible.
As someone summarizes in another comment[0], keep the chattiness as minimal as possible. By chattiness I understand they mean, pack as much data as you can in the same Keep-Alive connection. Avoid making new HTTP requests as much as possible, as each one might get assigned to a new Onion route making things slow.
If you can ship your website to the browser in a single connection, you've won.
I've always been impressed by performance of these big Onion sites, they really push the limits of software engineering creativity, given these constraints and nature of Tor.
--
[0]: https://news.ycombinator.com/item?id=49872320
EDIT: Formatting of bullet points.
To make sure once in the .onion, you never leave the .onion
Know this: the "dark web" is not for people who just want to own your domain name. It's for SECURITY and that use case is going to drive all their decisions. And if it wipes out every community in the entire tor dark web? So be it. And they'll do it again. Don't build your communities on the sand that is the dark web. You won't like the result.
> HiddenServicePort 80 127.13.37.1:8080
> listen 127.13.37.1:8080;
This way, strangers won't be able to connect to a service bound to 127.0.0.1, should you ever decide to re-use the port and forget to disable the hidden service.
You'll also need to use separate ports and/or bind addresses if you host multiple hidden services and don't want people to correlate them - if nginx doesn't match the Host header, it will serve whichever site comes first alphabetically.
1. If you want to improve page load speed you need to buy a HTTPS certificate so you are not limited to HTTP/1.1. Multiplexing in HTTP/2 is important for getting sites to load fast.
2. You can set the HiddenServiceExportCircuitID configuration to pass the circuit id to your web server for telemetry or anti abuse purposes. Otherwise your logs will say that all users are coming from the same IP.
Which raises the question: why not just trust self-signed certificates on onion services? From my brief look it seems to be because the Tor project views the primary purposes of HTTPS on onion services to be other things rather than just http/2 support: http/2 isn't even mentioned on their page about https for onion services (https://community.torproject.org/onion-services/advanced/htt...). Unfortunate.
Trying to push hidden services to stay on HTTP is going against what the rest of the web is doing and as a minority of web traffic it really should be aligned to the rest of the web and also require HTTPS. Yes, it's technically wasteful, but reduces both work and security risk by keeping security models aligned with the rest of the web.
(There are solutions for CGNAT - https://david.alvarezrosa.com/posts/self-hosting-behind-cgna...)