Holding page for a request

Hi,

I am trying to create a holding page when the request exceeds the limit

if my maxconn is 10, then when the 11th connection comes I want to show the user a temporary holding page saying they are in a queue and process the request when the connection is available.

could someone help how to approach this design? is this achievable using HAProxy and Lua?

current setup has a Lua service which sends a response of html page for the 11th connection, this html page has a javascript to resubmit the page again after few seconds. Javascript reload is failing in certain browsers so we want to try a different approach for the holding page.