apache2 reverse proxy configuration - apache

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]