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

Nginx is a high‑performance web and reverse‑proxy server that uses little memory and handles massive concurrency, making it a popular alternative to Apache for large Chinese companies such as Taobao, JD, Baidu, Sina, NetEase, and Tencent.

1. Custom 404 error page

Before optimization, accessing a non‑existent page returns the default "404 Not Found" message.

# firefox http://192.168.4.5/xxxxx // access a missing page

Modify nginx.conf to define a custom error page:

# vim /usr/local/nginx/conf/nginx.conf
... 
error_page 404 /404.html; // custom error page
...

Create /usr/local/nginx/html/404.html with your own content, e.g.: Oops, No NO no page … Reload Nginx and the client now sees the custom 40x page.

# firefox http://192.168.4.5/xxxxx // now shows custom page

Common HTTP status codes are shown in the following image:

2. View server status information

Enable the --with-http_stub_status_module when compiling Nginx to activate the status page.

# tar -zxvf nginx-1.12.2.tar.gz
# cd nginx-1.12.2
# ./configure \
    --with-http_ssl_module          // enable SSL
    --with-stream                    // enable TCP/UDP proxy
    --with-http_stub_status_module   // enable status page
# make && make install

Start Nginx and use ss (or netstat) to view listening ports. Useful ss options:

-a : show all ports

-n : numeric output

-t : TCP ports

-u : UDP ports

-l : listening sockets

-p : process name

# netstat -anptu | grep nginx
# ss -anptu | grep nginx

Add a location block in nginx.conf to expose the status page:

# cat /usr/local/nginx/conf/nginx.conf
... 
location /status {
    stub_status on;
    #allow IP;
    #deny IP;
}
... 
# /usr/local/nginx/sbin/nginx -s reload

Query the status page:

# curl http://192.168.4.5/status
Active connections: 1
server accepts handled requests
 10 10 3
Reading: 0 Writing: 1 Waiting: 0

Explanation of the fields:

Active connections – current active connections

Accepts – total accepted connections

Handled – total handled connections (usually equals accepts)

Requests – total client requests

Reading – connections reading request headers

Writing – connections writing responses

Waiting – idle connections waiting for a request

3. Increase Nginx concurrency

Before tuning, an ab test with 2000 concurrent requests fails with "Too many open files".

# ab -n 2000 -c 2000 http://192.168.4.5/
socket: Too many open files (24)

Adjust nginx.conf:

# vim /usr/local/nginx/conf/nginx.conf
... 
worker_processes 2;               // match CPU cores
events {
    worker_connections 65535;   // max connections per worker
}
... 
# /usr/local/nginx/sbin/nginx -s reload

Raise Linux file‑descriptor limits:

# ulimit -a                     // view limits
# ulimit -Hn 100000            // set hard limit (temporary)
# ulimit -Sn 100000            // set soft limit (temporary)
# edit /etc/security/limits.conf
* soft nofile 100000
* hard nofile 100000

Retest with ab – the server now handles the load.

4. Expand request header buffer

A script generating a very long URL triggers a "414 Request-URI Too Large" error.

# cat lnmp_soft/buffer.sh
#!/bin/bash
URL=http://192.168.4.5/index.html?
for i in {1..5000}; do
    URL=${URL}v$i=$i
done
curl $URL   // results in 414 error

Increase header buffers in nginx.conf:

# vim /usr/local/nginx/conf/nginx.conf
... 
http {
    client_header_buffer_size 1k;
    large_client_header_buffers 4 4k;
}
# /usr/local/nginx/sbin/nginx -s reload

Rerun the script – the request succeeds.

5. Browser local cache for static assets

In Firefox, open about:cache to view cache entries, then clear the cache.

Configure Nginx to set a 30‑day expiration for common static file types:

# vim /usr/local/nginx/conf/nginx.conf
server {
    listen 80;
    server_name localhost;
    location / {
        root html;
        index index.html index.htm;
    }
    location ~* \.(jpg|jpeg|gif|png|css|js|ico|xml)$ {
        expires 30d; // client cache for 30 days
    }
}
# cp /usr/share/backgrounds/day.jpg /usr/local/nginx/html
# /usr/local/nginx/sbin/nginx -s reload

After reloading, accessing an image with Firefox shows the file cached for the defined period.