Load-Balance servers monitor issue

[drivard]

Hi,

I am trying to setup pfsense as a load-balancer, it is not the first time I configure it but this time I want more than a simple port health check.
Here is the setup:

WAN: 10.255.2.15
LAN: 192.168.1.0/24
DHCP: 192.168.1.100/192.168.1.200

mysql-db1 -> 192.168.1.21
mysql-db2 -> 192.168.1.22
mysql-db3 -> 192.168.1.23

What I am trying to accomplish a load-balancer that load-balance port 3306 but monitors port 80 to check the mysql health, but I can't figure this out. I have mysql servers that have an Apache server running and if you request the root http://192.168.1.21/ it will execute a PHP script and in this script I made some MySQL health check. the apache servers return the perfect answer at the moment if I call them in the browser.

So I configured a new monitor with type HTTP with path / and host: empty because I am unsure of what to put there, but I tried the WAN ip, I tried a VIP but still I am having some issues.  Then I configured a pool with my 3 servers, the port I specified was 3306 and the monitor is my newly created http monitor. Then I created my virtual server that point to my WAN ip and port 3306.

How can I accomplsih this setup?