Monitoring Individual Application Tiers

I've seen this done various ways, but I think the lessor of evils is to let the web server determine if the tiers behind it are down and reflect that status by either shutting down its web-service or presenting a "down" status on a healthcheck page that the F5 is monitoring.

Another lessor-of-evils option is to create and apply an F5 monitor that sends test transactions to the web-servers. That test-transaction would need to be processed similar to real application transactions, which would allow the F5 to receive some expected response if the transaction was successful through all tiers.