URL rewrite rule to capture response status 503 and redirect

Hi,

I have a site defined in IIS as "mysite_dot_com"

I have two applications defined under it as follows: "/myapp" and "/sec/myapp"

"mysite_dot_com/myapp" is our main application URL and servicing all http requests by passing to a downstream server. Under a failure a condition, "/myapp" will return a response with status code "503/Service Unavailable".

I need help to capture this event ( i.e. 503 event), using outbound rule and rewrite ( and redirect) the URL as "7.5 mysite_dot_com/sec/myapp". (no worry on "/sec" part, it can be trimmed before passing to my downstream server).

Alternative suggestions are most welcome.

Thanks a lot.

-Ram