The error message you're seeing - "Invalid command 'ProxyPass'" - typically occurs when Apache's proxy modules aren't properly configured or loaded, despite what the debug output might suggest. The key detail here is that while proxy_http_module appears in your debug output, you're missing its fundamental dependency: mod_proxy.so.

Apache's proxy functionality works in a layered architecture:

mod_proxy.so (core proxy module)
├── proxy_http_module (HTTP protocol support)
├── proxy_ajp_module (AJP protocol support)
└── ... other protocol modules

Uncomment and activate the core proxy module in your httpd.conf:

# Old (incorrect):
#LoadModule proxy_module modules/mod_proxy.so

# New (correct):
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

Here's a verified working SSL proxy configuration:

<VirtualHost _default_:443>
    SSLEngine on
    SSLCertificateFile "conf/ssl/server.crt"
    SSLCertificateKeyFile "conf/ssl/server.key"
    
    # REQUIRED proxy modules
    ProxyRequests Off
    ProxyPreserveHost On
    SSLProxyEngine On
    
    # Proxy configuration
    ProxyPass /app/ http://backend-server:8080/
    ProxyPassReverse /app/ http://backend-server:8080/
    
    # Security restrictions
    <Proxy *>
        Require all granted
    </Proxy>
</VirtualHost>

After making changes:

1. Run httpd -t to test configuration syntax
2. Check loaded modules with httpd -M
3. Look for both proxy_module and proxy_http_module in output

• Module load order matters - core modules must load first
• Windows paths require double backslashes or forward slashes
• Firewall may block internal proxy connections

If issues persist, enable detailed logging:

LogLevel debug
ProxyVia On
SSLProxyCheckPeerCN off
SSLProxyCheckPeerName off

Many developers encounter this puzzling situation where Apache clearly shows proxy_http_module loading in debug output, yet stubbornly claims ProxyPass is an invalid command. Here's what's really happening under the hood.

The critical detail often missed is that mod_proxy_http.so depends on mod_proxy.so being loaded first. Even though your debug output shows proxy_http_module loading, the parent module isn't active. Here's the proper loading sequence:

# Essential proxy modules must load in this order:
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

When working with SSL VirtualHosts, there are additional considerations. The ProxyPass directive in your httpd-ssl.conf needs proper context. Here's a working example:

<VirtualHost _default_:443>
    SSLEngine on
    SSLCertificateFile "conf/ssl/server.crt"
    SSLCertificateKeyFile "conf/ssl/server.key"
    
    # Proxy configuration
    <IfModule mod_proxy.c>
        ProxyRequests Off
        ProxyPreserveHost On
        ProxyPass / http://backend-server:8080/
        ProxyPassReverse / http://backend-server:8080/
    </IfModule>
</VirtualHost>

For quick verification of loaded modules, use:

httpd -M | grep proxy

You should see both proxy_module and proxy_http_module in the output.

Watch out for these configuration mistakes:

• Module load order matters - parent modules must load before their dependencies
• Check for duplicate LoadModule directives
• Verify module files exist in the specified path

For complex proxy setups with SSL termination:

<VirtualHost *:443>
    ServerName api.example.com
    SSLEngine On
    # SSL certificates configuration...
    
    # Proxy configuration with custom timeout
    ProxyTimeout 300
    ProxyPass /api/ http://internal-api-cluster/
    ProxyPassReverse /api/ http://internal-api-cluster/
    
    # Headers management
    RequestHeader set X-Forwarded-Proto "https"
    RequestHeader set X-Forwarded-Port "443"
</VirtualHost>