When migrating from IIS to Apache while maintaining backward compatibility, the standard approach of proxying subdomains (like iis.example.com) won't work when application licensing (like dotnetCharting) is tied to the primary domain. We need to proxy specific paths (www.example.com/charts/) while serving other content from Apache.

Here's a complete VirtualHost configuration that proxies /subdir/ to your IIS server while serving other content from Apache:

<VirtualHost *:80>
    ServerName www.example.com
    
    # Main document root for Apache content
    DocumentRoot /var/www/html
    
    # Proxy configuration for the subdirectory
    <Location /subdir/>
        ProxyPass http://iis-internal-ip/
        ProxyPassReverse http://iis-internal-ip/
        ProxyPreserveHost On
        
        # Additional headers if needed for your dotnetCharting
        RequestHeader set Host "www.example.com"
        RequestHeader set X-Forwarded-Proto "http"
    </Location>
    
    # Other Apache configuration...
</VirtualHost>

If your IIS application generates absolute URLs, you'll need mod_rewrite to fix them:

RewriteEngine On
RewriteRule ^/subdir/(.*) http://iis-internal-ip/$1 [P]
ProxyPassReverse /subdir/ http://iis-internal-ip/

For HTTPS configurations, add these SSL-specific directives:

<VirtualHost *:443>
    SSLEngine on
    SSLCertificateFile /path/to/cert.pem
    SSLCertificateKeyFile /path/to/key.pem
    
    <Location /subdir/>
        ProxyPass https://iis-internal-ip/
        ProxyPassReverse https://iis-internal-ip/
        RequestHeader set X-Forwarded-Proto "https"
    </Location>
</VirtualHost>

After configuration, test with these commands:

# Check Apache syntax
apachectl configtest

# Test the proxy response
curl -v http://localhost/subdir/
curl -v https://localhost/subdir/ -k

If you encounter 502 errors or misrouted requests:

1. Verify network connectivity between Apache and IIS
2. Check IIS bindings accept requests from Apache
3. Inspect Apache error logs (/var/log/apache2/error.log)
4. Ensure mod_proxy and mod_proxy_http are enabled

For dotnetCharting specifically, you may need to add:

RequestHeader set Referer "http://www.example.com/subdir/"

When migrating from IIS to Apache while maintaining legacy system accessibility, developers often face a unique challenge when proprietary software licensing is tied to domain names. In our case, dotnetCharting's domain-based licensing requires creative reverse proxy configuration.

Apache's mod_proxy and mod_proxy_http modules can handle subdirectory proxying through careful VirtualHost configuration. Here's the technical implementation:

    ServerName www.example.com
    
    # Main document root for Apache content
    DocumentRoot /var/www/html
    
    # Proxy configuration for the subdirectory
    ProxyPass /subdir http://iis-server.example.com/
    ProxyPassReverse /subdir http://iis-server.example.com/
    
    # Additional directives to handle URL rewriting
    
        ProxyPassReverse /
        ProxyPreserveHost On
        RequestHeader set X-Forwarded-Proto "http"
    

The critical aspect is maintaining the original domain context for dotnetCharting. The ProxyPreserveHost On directive ensures IIS receives the original Host header, making the licensing validation work seamlessly.

For more complex scenarios, consider these additional configurations:

# For SSL termination at Apache level

    SSLEngine on
    SSLCertificateFile /path/to/cert.pem
    SSLCertificateKeyFile /path/to/key.pem
    
    ProxyPass /subdir http://iis-server.example.com/
    ProxyPassReverse /subdir http://iis-server.example.com/
    
    # Handle WebSocket connections if needed
    ProxyPass /subdir/ws ws://iis-server.example.com/ws
    ProxyPassReverse /subdir/ws ws://iis-server.example.com/ws

If you encounter 502 errors or broken assets:

• Verify mod_proxy and mod_proxy_http are enabled
• Check SELinux/permissions if running on Linux
• Inspect Apache error logs for detailed proxy errors
• Test connectivity between Apache and IIS servers

For production environments, add these directives to your proxy configuration:

ProxyRequests Off
ProxyTimeout 300
ProxyVia On
ProxyBadHeader Ignore