Web Servers

Apache Virtual Hosts and Server Administration

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At a glance#

Purpose: Configure and administer Apache HTTP Server, including virtual hosts, modules, logging and reverse proxying.
Applies to: Apache 2.4 on Ubuntu/Debian and RHEL-family systems.
Risk: Medium — a config error can take every hosted site down at once.
Time: 45 minutes for a new virtual host.

Overview#

Apache serves multiple sites from one server using virtual hosts, matched by the Host header. The two distribution families lay Apache out very differently, which is the most common source of confusion when moving between servers:

	Ubuntu / Debian	RHEL / Rocky / AlmaLinux
Service	`apache2`	`httpd`
Config root	`/etc/apache2/`	`/etc/httpd/`
Main config	`apache2.conf`	`conf/httpd.conf`
Site configs	`sites-available/` + `sites-enabled/`	`conf.d/*.conf`
Enable a site	`a2ensite`	Drop a file in `conf.d/`
Modules	`a2enmod` / `a2dismod`	`conf.modules.d/*.conf`
Test config	`apache2ctl configtest`	`httpd -t`
Runs as	`www-data`	`apache`
Logs	`/var/log/apache2/`	`/var/log/httpd/`

Commands below show the Ubuntu form first; substitute from this table for RHEL.

Before you start#

Root or sudo access.
DNS already resolving the hostname to this server.
The document root path decided.

Confirm Apache is installed and running:

bash

apache2 -v || httpd -v
sudo systemctl status apache2 || sudo systemctl status httpd

Creating a virtual host#

1. Create the document root#

bash

sudo mkdir -p /var/www/example.com/public_html
sudo chown -R www-data:www-data /var/www/example.com
sudo chmod -R 755 /var/www/example.com
echo "<h1>example.com</h1>" | sudo tee /var/www/example.com/public_html/index.html

Note: On RHEL the web user is apache, not www-data. Getting this wrong produces 403 errors that look like a permissions bug in the application.

2. Create the virtual host file#

bash

sudo nano /etc/apache2/sites-available/example.com.conf

apache

<VirtualHost *:80>
    ServerName   example.com
    ServerAlias  www.example.com
    DocumentRoot /var/www/example.com/public_html

    <Directory /var/www/example.com/public_html>
        Options -Indexes +FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>

    ErrorLog  ${APACHE_LOG_DIR}/example.com-error.log
    CustomLog ${APACHE_LOG_DIR}/example.com-access.log combined
</VirtualHost>

Key directives:

Directive	Purpose
`ServerName`	Primary hostname this block answers for
`ServerAlias`	Additional hostnames
`Options -Indexes`	Prevents directory listing when no index file exists
`AllowOverride All`	Permits `.htaccess` — set to `None` if unused, it is faster
`Require all granted`	Apache 2.4 access control; the old `Allow from all` no longer works

Warning: Options -Indexes matters. Without it, Apache lists the contents of any directory lacking an index file, which routinely exposes backups, config files and database dumps.

3. Enable the site#

bash

# Ubuntu / Debian
sudo a2ensite example.com.conf
sudo apache2ctl configtest
sudo systemctl reload apache2

On RHEL the file just needs to live in /etc/httpd/conf.d/, then:

bash

sudo httpd -t
sudo systemctl reload httpd

Note: Use reload, not restart. Reload applies new configuration without dropping active connections. Always run the config test first — a reload with broken config is ignored, but a restart with broken config leaves Apache stopped.

4. Disable the default site#

The default site catches any request that matches no virtual host, and will serve the Apache placeholder page on unconfigured domains:

bash

sudo a2dissite 000-default.conf
sudo systemctl reload apache2

Common module tasks#

bash

# List loaded modules
apache2ctl -M

# Enable frequently needed modules
sudo a2enmod rewrite headers ssl proxy proxy_http deflate

# Disable one
sudo a2dismod status

sudo systemctl restart apache2

Modules require a restart, not a reload.

Reverse proxy to an application#

Common where an application server listens on localhost and Apache handles TLS and the public port:

apache

<VirtualHost *:80>
    ServerName app.example.com

    ProxyPreserveHost On
    ProxyPass        / http://127.0.0.1:8080/
    ProxyPassReverse / http://127.0.0.1:8080/

    <Proxy *>
        Require all granted
    </Proxy>

    ErrorLog  ${APACHE_LOG_DIR}/app-error.log
    CustomLog ${APACHE_LOG_DIR}/app-access.log combined
</VirtualHost>

bash

sudo a2enmod proxy proxy_http
sudo systemctl restart apache2

Note: ProxyPreserveHost On passes the original Host header through. Without it, applications generate redirect URLs pointing at 127.0.0.1 and login loops follow.

Redirects#

apache

# Whole site to HTTPS
<VirtualHost *:80>
    ServerName example.com
    Redirect permanent / https://example.com/
</VirtualHost>

# Single path
Redirect permanent /old-page /new-page

# Non-www to www
<VirtualHost *:80>
    ServerName www.example.com
    ServerAlias example.com
    RewriteEngine On
    RewriteCond %{HTTP_HOST} !^www\. [NC]
    RewriteRule ^(.*)$ https://www.%{HTTP_HOST}$1 [R=301,L]
</VirtualHost>

Log management#

bash

# Live tail
sudo tail -f /var/log/apache2/example.com-access.log
sudo tail -f /var/log/apache2/example.com-error.log

# Top client IPs
sudo awk '{print $1}' /var/log/apache2/example.com-access.log | sort | uniq -c | sort -rn | head -20

# Count responses by status code
sudo awk '{print $9}' /var/log/apache2/example.com-access.log | sort | uniq -c | sort -rn

# Requests returning 500
sudo awk '$9 == 500' /var/log/apache2/example.com-access.log | tail -20

# Most requested URLs
sudo awk '{print $7}' /var/log/apache2/example.com-access.log | sort | uniq -c | sort -rn | head -20

Log rotation is configured by the package in /etc/logrotate.d/apache2. Confirm it is working — busy sites fill a partition quickly:

bash

sudo logrotate -d /etc/logrotate.d/apache2

Performance basics#

bash

# Which MPM is in use
apache2ctl -V | grep MPM

event is the modern default and handles concurrency best. prefork is required only when using mod_php; switching to PHP-FPM allows event and uses far less memory.

Enable compression:

bash

sudo a2enmod deflate

apache

<IfModule mod_deflate.c>
    AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css \
                                  application/javascript application/json
</IfModule>

Check server status:

bash

sudo a2enmod status
sudo systemctl reload apache2
curl http://localhost/server-status?auto

Warning: Restrict /server-status to localhost. It exposes request details and client IPs.

Verification#

bash

# Config valid
sudo apache2ctl configtest

# Site responds with correct content
curl -sI http://example.com | head -1
curl -s http://example.com | head -5

# Virtual host actually matched
apache2ctl -S

# Listening on the expected ports
sudo ss -tulpn | grep -E 'apache|httpd'

apache2ctl -S is the fastest way to see which virtual host serves which name, and to spot overlapping ServerName entries.

Troubleshooting#

Symptom	Cause and fix
403 Forbidden	Permissions or a missing `Require all granted`. Check the web user can traverse every parent directory.
Default Apache page instead of the site	Virtual host not enabled, or `ServerName` does not match. Check `apache2ctl -S`.
Config test fails after edit	The output names the file and line. Fix before reloading.
Apache will not start after restart	Broken config, or another process on port 80. Check `sudo ss -tulpn
`.htaccess` rules ignored	`AllowOverride None`. Set to `All` for that directory.
500 Internal Server Error	Application error. Read the site's `ErrorLog` — Apache logs the cause there.
Wrong site served for a domain	Two virtual hosts share a `ServerName`, so the first match wins. Review `apache2ctl -S`.
Site works by IP but not hostname	DNS, not Apache. See the DNS troubleshooting article.
High memory usage	`prefork` MPM with `mod_php`. Move to PHP-FPM and the `event` MPM.

Apache Virtual Hosts and Server Administration

At a glance#

Overview#

Before you start#

Creating a virtual host#

1. Create the document root#

2. Create the virtual host file#

3. Enable the site#

4. Disable the default site#

Common module tasks#

Reverse proxy to an application#

Redirects#

Log management#

Performance basics#

Verification#

Troubleshooting#

Related#