Hi,
To not declare a real server down if one of its applications fail, you should configure your probes in your serverfarm, and (if not already done) create a serverfarm per application.
If you want to be able to redirect a request send to a failed serverfarm, you can configure a backup serverfarm in you L7 policy map like this:
serverfarm name1 backup name2
The second serverfarm should then be of the type:
serverfarm redirect name2
webhost-redirection relocation_string [301 | 302]
where the relocation_string is the URL that should be used, 301 is permanently moved and 302 is temporarily.
For the relocation_string, you can use following special characters:
%h Inserts the hostname from the request Host header
%p Inserts the URL path string from the request
Mor info can be found in this doc:
http://www.cisco.com/en/US/docs/interfaces_modules/services_modules/ace/v3.00_A2/configuration/slb/guide/slbgd.html
Hope this helps.
Kr,
Dario