Boost Nginx Performance: Custom 404 Pages, Status Monitoring, and Concurrency Tuning

1. Custom 404 Error Page

Before optimization, a request for a non‑existent URL returns the default "404 Not Found" page. By editing /usr/local/nginx/conf/nginx.conf and adding error_page 404 /404.html;, you can serve a custom HTML file (e.g., /usr/local/nginx/html/404.html) and then reload Nginx with nginx -s reload. After the change, browsers display the custom 404 page.

2. Viewing Server Status Information

Compile Nginx with the --with-http_stub_status_module flag to enable the status module. In the configuration file, add a location block:

location /status {
    stub_status on;
    #allow 127.0.0.1;
    #deny all;
}

Reload Nginx and query the page (e.g., curl http://192.168.4.5/status) to see metrics such as active connections, accepts, handled, requests, reading, writing, and waiting. You can also view listening ports with netstat -anptu | grep nginx or ss -anptu | grep nginx. The ss command works on RHEL7 as a drop‑in replacement for netstat.

3. Increasing Nginx Concurrency

Initial high‑concurrency testing with ab -n 2000 -c 2000 http://192.168.4.5/ may fail with "Too many open files". Increase concurrency by editing nginx.conf:

worker_processes 2;               # match CPU cores
events {
    worker_connections 65535;   # max connections per worker
}

Then reload Nginx. Adjust Linux limits to allow more open files:

# ulimit -Hn 100000   # hard limit (temporary)
# ulimit -Sn 100000   # soft limit (temporary)
# edit /etc/security/limits.conf and add:
* soft nofile 100000
* hard nofile 100000

Retest with ab after the changes.

4. Expanding Header Buffer Size

A script that builds a very long URL (5000 query parameters) triggers a "414 Request-URI Too Large" error. Fix this by increasing header buffers in the http block of nginx.conf:

http {
    client_header_buffer_size 1k;
    large_client_header_buffers 4 4k;
}

Reload Nginx and rerun the script; the request succeeds.

5. Browser Local Cache for Static Assets

In Firefox, entering about:cache shows cached resources. To enable long‑term client caching, add an expires directive for static file types:

location ~* \.(jpg|jpeg|gif|png|css|js|ico|xml)$ {
    expires 30d;   # cache for 30 days
}

After reloading Nginx, access a static image (e.g., http://192.168.4.5/day.jpg) and verify via about:cache that the file is cached with the correct expiration.