Web Dispatcher as Reverse Proxy

Hi All,

We are trying to redirect the user to a different URL when SAP ECC AS is down.
User is interacting with the application through a simple HTML Based web application(No Enterprise Portal/WDA).

After doing a lot of research, i found out that we should configure the Web Dispatcher as Reverse Proxy to achieve this. But, i am only getting information on these in context of SAP Enterprise Portal.

Kindly, share some resources or suggestions in case of only SAP NW ECC and External Web Application related landscapes.

Thanks

Sahil