How can you run two instances of Nginx on the same machine without Docker?

I've been searching for how to install two instances of nginx on my server without Docker/containerization, but I've found little results. How can this be done?

Possible use cases:

• You have two applications and you don't want one to take down both if one crashes. (This is my scenario.)
• You want to give an end user control of the nginx config and process/service. Since the processes are isolated from each another, they can be stopped/started & configured independently.

I've managed to solve this problem using Debian Bullseye, but the steps should be similar for other Linux flavors.

• Find the nginx service file: find / -iname "nginx.service" -type f -ls

• Copy the service file to /etc/systemd/system. Here is the command for my scenario: cp /usr/lib/systemd/system/nginx.service /etc/systemd/system/nginx2.service (the filename becomes the name of the service, so choose carefully)

• Copy the nginx config to another folder: cp -rp /etc/nginx /etc/nginx2

• Edit the nginx2 service file: nano /etc/systemd/system/nginx2.service. Change these lines:

   [Service]
   PIDFile=/run/nginx2.pid
   ExecStartPre=/usr/sbin/nginx -t -c /etc/nginx2/nginx.conf -q -g 'daemon on; master_process on;'
   ExecStart=/usr/sbin/nginx -c /etc/nginx2/nginx.conf -g 'daemon on; master_process on;'
   ExecReload=/usr/sbin/nginx -c /etc/nginx2/nginx.conf -g 'daemon on; master_process on;' -s reload
   ExecStop=-/sbin/start-stop-daemon --quiet --stop --retry QUIT/5 --pidfile /run/nginx2.pid
  

• Edit the nginx config file: nano /etc/nginx2/nginx.conf. Change these lines:

   pid /run/nginx2.pid;
   include /etc/nginx2/modules-enabled/*.conf;
  
   http {
  
           include /etc/nginx2/mime.types;
  
           access_log /var/log/nginx/access2.log;
           error_log /var/log/nginx/error2.log;
  
           include /etc/nginx2/conf.d/*.conf;
           include /etc/nginx2/sites-enabled/*;
   }
  

• Delete the symbolic link for the default site, as it points to the original nginx instance's folder: rm /etc/nginx2/sites-enabled/default. ( To re-create, ln -s /etc/nginx2/sites-available/default /etc/nginx2/sites-enabled/default.)

• You cannot have two nginx instances listening on the same port & IP address (unless you're doing port sharding, which is an advanced topic...), so you must change the port(s) to not conflict with the first instance.

• Inform systemd of the new service: systemctl daemon-reload

• Enable the new service: systemctl start nginx2

• Enjoy!