Redirecting and masquerading the result for the client.

Here's a very basic iRule that will catch headers and payload data. Apply an empty STREAM profile to the virtual server to enable STREAM processing in the iRule. If you don't need to catch payload, then you can remove the STREAM profile and all of the STREAM statements.

when HTTP_REQUEST {
    STREAM::disable
    HTTP::header remove Accept-Encoding

     inbound: replace Host header with internal name
    HTTP::header replace Host "foo.example.com"
}
when HTTP_RESPONSE {
     outbound: replace Host value (if it exists) in all headers
    foreach x [HTTP::header names] {
        if { [HTTP::header $x] contains "foo.example.com" } {
            HTTP::header replace $x [string map {"foo.example.com" "external.domain.com"} [HTTP::header $x]]
        }
    }

     outbound: replace Host value in payload
    STREAM::expression {@foo.example.com@external.domain.com@}
    STREAM::enable
}