Listen to Non-Standard Ports with Apache

Linux Apps Tutorials - Herong's Tutorial Examples

∟Running Apache HTTP Server (httpd) on Linux Systems

∟Listen to Non-Standard Ports with Apache

This section provides a tutorial example on how to add virtual hosts to listen to additional ports other than standard ports (80 and 443) with and without systemd Socket Activation service.

By default, Apache HTTP Server is configured to use 2 standard TCP ports: 80 for HTTP connections and 443 for HTTP over SSL/TLS connections. And these 2 ports are managed by the Socket Activation module in the "systemd" program.

If you check the list of "systemd" service unit files using the "systemctl" command, you will see 2 services related to "httpd":

herong$ systemctl list-unit-files | grep -e "httpd\..*"

httpd.service                              enabled  
httpd.socket                               enabled

The output of the "httpd.service" status confirms that it is listening on ports 80 and 443:

herong$ systemctl status httpd.service

* httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; ...)
  Drop-In: /usr/lib/systemd/system/httpd.service.d
           |-php-fpm.conf
   Active: active (running) since Sat 2024-03-30 20:10:41
  Process: 736003 ExecReload=/usr/sbin/httpd $OPTIONS ...
  ...
... httpd[443337]: Server configured, listening on: port 443, port 80

The output of the "httpd.socket" status confirms that the Socket Activation module is managing ports 80 and 443:

herong$ systemctl status httpd.socket

* httpd.socket - Apache httpd Server Socket
   Loaded: loaded (/usr/lib/systemd/system/httpd.socket; enabled; ...)
  Drop-In: /usr/lib/systemd/system/httpd.socket.d
           |-10-listen443.conf
   Active: active (listening) since Mon 2024-03-25 08:31:39
   Listen: [::]:80 (Stream)
           [::]:443 (Stream)
    Tasks: 0 (limit: 48033)

Port 80 is defined in "httpd.socket" configuration file:

herong$ more /usr/lib/systemd/system/httpd.socket

...
[Socket]
ListenStream=80
NoDelay=true
DeferAcceptSec=30

Port 443 is defined in a drop-in file added by the "mod_ssl" package:

herong$ more /usr/lib/systemd/system/httpd.socket.d/10-listen443.conf 

# This file is part of mod_ssl. It enables listening on port 443 when
# socket activation is used.

[Socket]
ListenStream=443

Using Socket Activation module to manage TCP port sockets is more efficient than letting "httpd" to manage them directly. But it requires extra configuration to add additional ports.

For example, if you try to add a virtual host to listening on 8080 in an extra Apache HTTP server configuration file:

herong$ sudo vi /etc/httpd/conf.d/extra.conf

Listen 8080

<VirtualHost _default_:8080>
  DocumentRoot /var/www/extra
</VirtualHost>

You will see the following error when re-starting the server:

herong$ sudo systemctl restart httpd.service
Job for httpd.service failed because the control process exited with error code.
See "systemctl status httpd.service" and "journalctl -xe" for details.

herong$ systemctl status httpd.service
AH00526: Syntax error on line 1 of /etc/httpd/conf.d/extra.conf:
Systemd socket activation is used, but this port is not configured in systemd

To fix this error, you need to add your own drop-in file to define port 8080, in the same way as the "mod_ssl" package. And restart the "httpd.socket" and "httpd.service" services:

herong$ sudo vi /usr/lib/systemd/system/httpd.socket.d/20-extra.conf 

[Socket]
ListenStream=8080

herong$ sudo systemctl restart httpd.socket 
herong$ sudo systemctl restart httpd.service

If managing httpd ports with Socket Activation gives you too much trouble, you can disable it, and let httpd to manage them directly:

herong$ sudo systemctl stop httpd.service

herong$ sudo systemctl stop httpd.socket 
herong$ sudo systemctl disable httpd.socket 

herong$ sudo systemctl start httpd.service