The error occurs when you place Nginx's main configuration directives inside the wrong context. The worker_processes directive must be placed in the main configuration context (nginx.conf), not within a server block.

Here's how your configuration should be properly structured:

# Main context in nginx.conf
worker_processes 4;
worker_rlimit_nofile 8192;
worker_priority 0;
worker_cpu_affinity 0001 0010 0100 1000;

events {
    worker_connections 1024;
}

http {
    include /etc/nginx/mime.types;
    
    server {
        server_name example.com;
        listen 80;
        root /var/www/devsites/trademob/tm-hp-v2/;
    }
}

Many administrators make these mistakes when configuring worker processes:

• Placing worker directives inside http or server blocks
• Using invalid CPU affinity masks
• Setting worker_processes to a number higher than available CPU cores

After modifying your configuration, always test it before applying changes:

sudo nginx -t

This will validate your configuration syntax and show any errors.

For optimal performance on a 8-core server with high traffic:

worker_processes auto;
worker_rlimit_nofile 200000;
worker_cpu_affinity auto;

events {
    worker_connections 16384;
    multi_accept on;
    use epoll;
}

This configuration automatically matches worker processes to CPU cores and increases file handle limits for high traffic scenarios.

When you encounter the error "worker_processes directive is not allowed here", it means you've placed a main-level Nginx directive inside a server block context. The worker_processes directive must be configured in the main configuration file (typically /etc/nginx/nginx.conf), not within server blocks defined in sites-enabled.

Here's how your configuration should be structured:

# Main context in nginx.conf
worker_processes 4;
worker_rlimit_nofile 8192;
worker_priority 0;
events {
    worker_connections 1024;
}

http {
    # Server block in separate file (sites-enabled/default)
    server {
        server_name example.com;
        listen 80;
        root /var/www/devsites/trademob/tm-hp-v2/;
    }
}

Many developers make these configuration mistakes:

• Placing main directives in server blocks
• Forgetting the events block
• Mixing main and http contexts

Instead, follow this hierarchy:
1. Main context (worker_processes, etc.)
2. Events context (worker_connections)
3. Http context (all server blocks)

After making changes, always test your configuration:

sudo nginx -t
sudo systemctl restart nginx

For optimal performance on a 4-core server:

worker_processes auto;
worker_cpu_affinity auto;
worker_rlimit_nofile 200000;
events {
    worker_connections 16384;
    multi_accept on;
    use epoll;
}