If you are trying to use F5 Big IP LTM (Local Traffic Manager) to load balance webservers running Lighttpd and have configured default http health monitor from F5, you would notice that the F5 would treat the servers as non responsive and mark then down.
This is because the send string in the default monitor is configured as GET /\r\n which is not accepted by few standard webservers like lighttpd.
A simple solution to this problem is to create a custom monitor with the help of default http monitor.