Take some of the HTTP load away from lila. WIP!
Clients connected to a tournament page request new data about the tournament every 4s or so, with XHR HTTP requests.
Each player requests information about a different leaderboard page: the one they're in.
When a tournament has 17k connected clients, like it happened during the Agadmator Arena, then lila has to serve about 5k tournament update requests per second.
It's too much. Even tho most of the data is cached by lila, these requests are authenticated and have a cost. lila usually serves at most 2k requests per second, and is not designed to suddenly serve 5k/s more.
So, the plan is to have a new service handle these tournament update requests. It gets info about ongoing tournaments from lila, and propagates it to the clients.
Much like lila-ws moved the websocket traffic away from lila, lila-http handles some of the heavy HTTP traffic.
It may be expanded to other areas than just the arena tournaments in the future.
One goal of lila-http is to be optional. Lichess should work just fine without it. It means that lila and lila-http can handle the same requests in the same way.
This simplifies dev environments, which won't need to install lila-http, and makes production more resilient to lila-http restarts or outages.
This goal is a nice-to-have, not a must-have, and might be dropped in the future if it proves to be too inconvenient.
It could have been done in scala, like lila-ws. But I saw this as an opportunity to learn rust, which I know is a fantastic language.
I value strong static typing very highly, and both scala and rust have it. Haskell would be an other option. Go, not so much.