When implementing a multi-server infrastructure, we often need to route specific subdomains to different backend servers while maintaining port 80 accessibility. The key requirement here is to avoid port-based redirection (like :81) while preventing redirect loops.

Ensure these modules are enabled in Server A (192.168.0.5):

sudo a2enmod proxy
sudo a2enmod proxy_http
sudo a2enmod proxy_balancer
sudo a2enmod lbmethod_byrequests
sudo a2enmod rewrite
sudo a2enmod ssl
sudo systemctl restart apache2

Here's the proper virtual host setup for Server A to proxy requests for owncloud.mydomain.com to Server B:

<VirtualHost *:80>
    ServerName owncloud.mydomain.com
    ServerAdmin admin@mydomain.com
    
    ProxyPreserveHost On
    ProxyPass / http://192.168.0.10/
    ProxyPassReverse / http://192.168.0.10/
    
    ErrorLog ${APACHE_LOG_DIR}/owncloud_error.log
    CustomLog ${APACHE_LOG_DIR}/owncloud_access.log combined
</VirtualHost>

Make sure your DNS records point both the main domain and subdomain to Server A's public IP:

mydomain.com.      IN  A      203.0.113.45
owncloud.mydomain.com. IN  A  203.0.113.45
www.mydomain.com.  IN  CNAME  mydomain.com.

On Server B (192.168.0.10), ensure Apache is configured to accept requests from Server A:

<VirtualHost *:80>
    ServerName owncloud.mydomain.com
    DocumentRoot /var/www/owncloud
    
    <Directory /var/www/owncloud>
        Options FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>
</VirtualHost>

If you encounter redirect loops, add these directives to Server A's configuration:

ProxyRequests Off
<Proxy *>
    Require all granted
</Proxy>

For HTTPS implementation, modify the virtual host with these additions:

<VirtualHost *:443>
    ServerName owncloud.mydomain.com
    SSLEngine on
    SSLCertificateFile /path/to/cert.pem
    SSLCertificateKeyFile /path/to/privkey.pem
    
    ProxyPreserveHost On
    ProxyPass / http://192.168.0.10/
    ProxyPassReverse / http://192.168.0.10/
</VirtualHost>

Add these directives to improve proxy performance:

ProxyRequests Off
ProxyTimeout 300
ProxyBadHeader Ignore
ProxyIOBufferSize 8192

After configuration, test with these commands:

sudo apachectl configtest
sudo systemctl restart apache2

Verify the routing works by accessing http://owncloud.mydomain.com from an external network while monitoring both servers' access logs.

---

When working with multiple Apache servers in an internal network, you might want to route specific subdomains to different backend servers while maintaining port 80 accessibility. Here's how I solved this exact configuration challenge.

In my setup:

• Server A (192.168.0.5): Primary server handling DNS, mail (webmail.mydomain.com), and main website (www.mydomain.com)
• Server B (192.168.0.10): Dedicated server running ownCloud

Initially, attempts to proxy requests to Server B resulted in redirect loops because:

1. The proxy configuration wasn't properly isolating the subdomain traffic
2. Server A kept intercepting the ownCloud requests meant for Server B
3. Missing ProxyPreserveHost directive caused host header issues

Here's the virtual host configuration that finally worked on Server A:

<VirtualHost *:80>
    ServerName owncloud.mydomain.com
    
    ProxyPass / http://192.168.0.10/
    ProxyPassReverse / http://192.168.0.10/
    ProxyPreserveHost On
    
    # Important for preventing redirect loops
    ProxyRequests Off
    
    # Additional headers if needed
    RequestHeader set X-Forwarded-Proto "http"
    RequestHeader set X-Forwarded-Port "80"
</VirtualHost>

On the backend server (Server B), ensure these settings in httpd.conf or your virtual host:

<Directory "/var/www/owncloud">
    Options FollowSymLinks
    AllowOverride All
    Require all granted
    
    # Important for proxy setups
    SetEnvIf X-Forwarded-Proto https HTTPS=on
</Directory>

Make sure your DNS records point correctly:

• owncloud.mydomain.com A record → Server A's public IP
• Internal DNS or hosts file should resolve owncloud.mydomain.com to Server A's internal IP

If you encounter issues:

1. Check Apache error logs on both servers
2. Verify mod_proxy and mod_proxy_http are enabled: a2enmod proxy proxy_http
3. Test connectivity between servers: curl -I http://192.168.0.10
4. Ensure no conflicting virtual hosts or ServerName directives

When implementing this proxy setup:

• Consider adding IP restrictions if servers are internet-facing
• Implement SSL termination if needed (additional ProxyPass configuration required)
• Monitor proxy performance and connection counts

If you prefer using paths instead of subdomains:

<VirtualHost *:80>
    ServerName mydomain.com
    
    ProxyPass /owncloud http://192.168.0.10/
    ProxyPassReverse /owncloud http://192.168.0.10/
    
    # Rest of your main site configuration
</VirtualHost>

This configuration maintains cleaner URL structures while still routing requests to the appropriate backend server.