Apache proxy load balancing backend server failure detection

Question

Here\'s my scenario (designed by my predecessor):

Two Apache servers serving reverse proxy duty for a number of mixed backend web servers (Apache, IIS, Tomcat, etc.). T

Answer 1

http://httpd.apache.org/docs/2.4/mod/mod_proxy.html Section "BalancerMember parameters", property=retry:

If the connection pool worker to the backend server is in the error state, Apache httpd will not forward any requests to that server until the timeout expires. This enables [one] to shut down the backend server for maintenance, and bring it back online later. A value of 0 means always retry workers in an error state with no timeout.

However there are other failure conditions that wouldn't be caught using mod_whatever, for example, IIS backend running an application which is down. IIS is up so a connection can be made and a page can be read, it's just that the page will always be 500 internal server error. Here you will have to use failonerror to catch it and force the worker into an error state.

In all cases once the worker is in an error state traffic will not be directed to it. I've been trying different ways of consuming that first failure and retrying it but there always seems to be cases where an error page makes it back to the client.