Without optimization, Nginx defaults to allowing a maximum of one worker process with 512 connections and 60s timeout. 20 unique visitors per second will lead to 500 errors in less than a minute.
It does not matter how fast the backend is. A persistent HTTP connection will last 60 seconds following the latest client request, unless the browser goes out of its way to explicitly close the connection.
P.S. OP's website uses Apache but the same issue of overly conservative limits still apply.
There's no way the connection just sits idle and the worker can't serve other requests for the full timeout, right? That just sounds... Wrong. And is not consistent with load testing I've done before with a nginx setup
There are multiple strategies for caching in the server, without them IIRC the php code will be interpreted on each request, files parsed, and obviously hit the database for each request.
There's fastcgi caching in nginx, php opcode in php-fpm, and WP specific cave plugins like Super Cache. At least this was the case ~10 years ago.
Also for $5/mo you can use Cloudflare APO to cache WordPress pages at the edge. Yes it will cache even the "dynamic" pages (unless you're logged in of course)
That's fine, I was just listing another option. It should be noted you should still do server side caching. This just lets you serve from Cloudflare's caching layers too
Are you sure? My understanding was that nginx would fill up all free connections up to the max, but then would begin draining idle connections so it could create new ones for new visitors.
