URL rewrite (or HTTP forwarding) using iRule?

The HTTP response doesn't need to be manipulated, that's already too late.

If I understood Jatin correctly, he has one form pointing to the VS, but depending on a header value it needs to be "translated"/forwarded to different URIs towards the servers in the pool. Redirect is not allowed/possible, which would by the way also a little bit tricky with POST-requests.

I would go with a DGL like this:

ltm data-group internal /Common/header_uri_mapping {
    records {
        header1 {
            data /uri1
        }
        header2 {
            data /uri2
        }
    }
}

And an iRule like this:

WHEN_HTTP_REQUEST {
    set new_uri [class match -value [HTTP::header "header1"] equals header_uri_mapping]
    if { $new_uri ne "" }{
        HTTP::uri $new_uri
    }
}

Ciao Stefan 🙂