[try_files_is_evil_too] try_files without open_file_cache

What this check looks for

This plugin warns when try_files is used, but open_file_cache is not configured.

Why this is a problem

try_files checks the filesystem repeatedly to see whether files exist. Without caching, those checks translate into repeated stat() syscalls. Under load, that adds up quickly and can become one of the hottest spots on a busy server.

Bad configuration

location / {
    try_files $uri $uri/ /index.html;
}

This works, but every request may trigger multiple filesystem checks.

Better configuration

Enable open_file_cache to cache file metadata:

open_file_cache          max=10000 inactive=30s;
open_file_cache_valid    60s;
open_file_cache_min_uses 2;
open_file_cache_errors   on;

server {
    location / {
        try_files $uri $uri/ /index.html;
    }
}

Additional notes

Caching is not always appropriate. If you serve highly dynamic file trees that change constantly (or you are on a filesystem where metadata caching is risky), you may choose to skip it. If you do, at least be aware of the performance tradeoff and test under realistic load.