Check manual page of haproxy.server
HAProxy: Server Status
This check monitors the status of the servers of the HAProxy loadbalancer
for TCP and HTTP connections. It requires the mk_haproxy.freebsd agent
plugin to be installed on the FreeBSD host to be monitored.
The check is OK if the server indicates the status UP and either active
or backup. It is CRIT otherwise.
The name of backend and server, separated by a "/".
One service for each server is created.