apache2 reverse proxy configuration

Question

I have one application that listens on TCP 127.0.0.1:81. I want to accomplish the following redirection:

www.example.com/?requestid=123456 --> http://127.0.0.1:81/?requestid=123456
www.example.com/ANYTHING_ELSE --> MY_IP_THAT_APACHE_LISTENS_ON

My understanding is that if I will not rewrite something explicitly, it will follow the regular path to the /var/www/html.

My /etc/apache2/sites-enabled/000-default.conf configuration:

<VirtualHost *:80>
        ServerName example.com
        ServerAdmin example@example.com
        DocumentRoot /var/www/html
        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

    <Location />
        RewriteEngine On
        RewriteRule ^/?requestid(.*)$ http://127.0.0.1:81/$1 [P]
        ProxyPassReverse http://127.0.0.1:81/
        Order allow,deny
        Allow from all
    </Location>

</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

Why it does not rewrite properly and keep hitting the normal patch?

Not Found
The requested URL /bullshit was not found on this server.

Apache/2.4.25 (Debian) Server at example.com Port 80

Answer 1

From RewriteRule Directive:

In VirtualHost context, The Pattern will initially be matched against the part of the URL after the hostname and port, and before the query string (e.g. "/app1/index.html"). This is the (%-decoded) URL-path.

If you wish to match against the hostname, port, or query string, use a RewriteCond with the %{HTTP_HOST}, %{SERVER_PORT}, or %{QUERY_STRING} variables respectively.

So, you will need something like this:

RewriteEngine On
RewriteCond %{QUERY_STRING} requestid=(.+)
RewriteRule ^/$ http://127.0.0.1:81/?requestid=%1 [P]