The error occurs when trying to use the <If> directive in Apache's VirtualHost configuration. The specific error message indicates that Apache doesn't recognize this as a valid command, which typically means either:

1. The required module isn't loaded
2. The syntax format is incorrect for your Apache version

The <If> directive requires mod_version to be enabled in Apache. Check if it's loaded with:

apache2ctl -M | grep version

If not enabled, activate it with:

sudo a2enmod version
sudo systemctl restart apache2

For Apache 2.4+ (which supports the expression syntax), you have several alternatives:

Option 1: Using IfDefine-like syntax

<If "%{HTTPS} != 'on'">
    Redirect / https://www.mydomain.com/
</If>

Option 2: Using mod_rewrite (more compatible)

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://www.mydomain.com/$1 [R=301,L]

The exact syntax depends on your Apache version:

• Apache 2.4+: Supports full expressions in <If> directives
• Apache 2.2: Only supports <IfVersion>, <IfModule>, etc.
• Apache 2.0: Very limited conditional logic

Here's a fully functional VirtualHost configuration for HTTPS redirection:

<VirtualHost *:80>
    ServerName www.mydomain.com
    ServerAlias mydomain.com
    DocumentRoot /var/www/html
    
    # Option A: Using If directive (Apache 2.4+)
    <If "%{SERVER_PROTOCOL} != 'HTTPS'">
        Redirect permanent / https://www.mydomain.com/
    </If>
    
    # Option B: Using rewrite (more compatible)
    RewriteEngine On
    RewriteCond %{HTTPS} !=on
    RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
</VirtualHost>

If you still encounter issues:

1. Check Apache version: apache2 -v
2. Verify syntax: apache2ctl configtest
3. Inspect error logs: tail -f /var/log/apache2/error.log
4. Test modules: apache2ctl -M

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When working with Apache's VirtualHost configuration, you might encounter the frustrating "Invalid command '<If'" error. This typically happens when trying to use the <If> directive in your VirtualHost configuration without having the required module enabled.

The <If> directive is part of Apache's mod_rewrite module, specifically introduced in Apache 2.4+. Before this version, you'd need to use different syntax for conditional redirects. Even with Apache 2.4+, you must ensure:

# Check if mod_rewrite is enabled
sudo a2enmod rewrite
sudo systemctl restart apache2

Here are three working approaches depending on your Apache version and needs:

1. For Apache 2.4+ with mod_rewrite

<VirtualHost *:80>
    ServerName mydomain.com
    <If "%{HTTPS} != 'on'">
        Redirect permanent / https://www.mydomain.com/
    </If>
</VirtualHost>

2. Using traditional mod_rewrite syntax

<VirtualHost *:80>
    RewriteEngine On
    RewriteCond %{HTTPS} off
    RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
</VirtualHost>

3. Simple Redirect directive (no conditions)

<VirtualHost *:80>
    Redirect permanent / https://www.mydomain.com/
</VirtualHost>

After making changes:

# Test configuration
sudo apachectl configtest

# Restart Apache
sudo systemctl restart apache2

# Check enabled modules
apache2ctl -M | grep rewrite

• Using SERVER_PROTOCOL instead of HTTPS (more reliable)
• Forgetting to enable mod_rewrite
• Mixing Apache 2.2 and 2.4 syntax
• Not using proper comparison operators (!= vs ne)

For high-traffic sites, consider these optimizations:

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{HTTPS} !=on
    RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L,NE]
</IfModule>

The NE flag prevents escaping of special characters, and wrapping in <IfModule> makes the configuration more portable.