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The best way to monitor a multi-tier app is to configure a monitor that makes a request to the load balanced tier that will only return the expected result if all underlying tiers are functional.

 

 

For example, if you are load balancing only the web tier, you can construct a monitor that makes an HTTP request via the web tier for a dynamic page that can only be properly generated if the app tier and the database are alive & well. cURL may be used to construct a scripted monitor if more than one request must be made to simulate the required transaction.

 

 

Monitoring only the app tier can be a bit trickier because the client may not be available on BIG-IP, but the same approach is recommended: Send a request to the tier you are LB'ing that reaches all the way through to the backend, and mark the middle tier server down if the expected response is not received. Netcat (nc) may be used to construct a scripted monitor if there is no builtin monitor type available, or if more than one request must be made to simulate the required transaction.

 

 

hth

 

/deb