How to tune worker_processes in Nginx

Tuning worker_processes helps Nginx use available CPU cores efficiently under load, improving throughput and stabilizing latency for busy sites and APIs.

In Nginx, a single master process manages a pool of worker processes, and each worker runs an event loop that accepts connections and services requests without spawning a process per client. The worker_processes directive controls how many workers exist, and auto selects a value based on detected CPU cores.

More workers is not always better: setting worker_processes above the effective core count can increase context switching and reduce performance. Overall concurrency is also bounded by worker_connections and OS file descriptor limits (systemd LimitNOFILE or ulimit -n), so tuning should be validated under representative traffic and checked with nginx -t before reload.

1. Check the number of CPU cores visible to the host or container.

   $ nproc
   4

   In container runtimes with CPU quotas, auto can oversubscribe CPU if the quota is not reflected in core detection; an explicit worker count aligned with the quota avoids wasted context switching.

2. Open the main Nginx configuration file.

   $ sudoedit /etc/nginx/nginx.conf

   If /etc/nginx/nginx.conf is not the active file, locate the configured path in nginx -V output (look for --conf-path=...).

3. Find the current worker_processes setting.

   $ sudo grep -n '^[[:space:]]*worker_processes' /etc/nginx/nginx.conf
   2:worker_processes auto;

4. Set worker_processes to auto in the main context.

   user www-data;
   worker_processes auto;
   pid /run/nginx.pid;

   Max concurrent connections is roughly worker_processes × worker_connections and is capped by OS file descriptor limits (LimitNOFILE or ulimit -n); if auto oversubscribes (common with CPU quotas or pinned cores), replace it with an explicit value such as worker_processes 2;.

5. Test the Nginx configuration for syntax errors.

   $ sudo nginx -t
   nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
   nginx: configuration file /etc/nginx/nginx.conf test is successful

6. Reload Nginx to apply the new worker count.

   $ sudo systemctl reload nginx

   On systems without systemd, send a reload signal with sudo nginx -s reload.

7. Confirm the nginx service is active after the reload.

   $ sudo systemctl status nginx
   ● nginx.service - A high performance web server and a reverse proxy server
        Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
        Active: active (running) since Sun 2025-12-14 12:00:00 UTC; 1min ago
   ##### snipped #####

8. Verify the running worker process count.

   $ pgrep -fc "nginx: worker process"
   4
   $ ps -o pid,cmd -C nginx
     PID CMD
     1462 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
     1463 nginx: worker process
     1464 nginx: worker process
     1465 nginx: worker process
     1466 nginx: worker process