Monitor which does not bring the service down for 20 seconds?

"The default setting for monitor is 5 sec interval and 16 sec timeout." That is not 5+16 until marked down. If a successful response isn't received with 16s it is marked down. The timeout value is the value that determines if a member is marked down. The interval is just how often a probe is sent. You could set your interval to 30s and have a timeout of 2s if you really wanted to. That would mean a probe is only sent every 30s and a member must respond within 2s or it will be marked down. Bets practice though is typically to set the timeout to the (interval*3)+1. That gives you the possibility of 3 failures before a member is marked down. I hope this explanation helps.