HTTPS to HTTP redirection from three external web urls to internal web urls using F5 as a revers proxy

Do all of the external sites work on the same IP or are they all discrete VIP's? If they are all discrete then it looks like adding the internal address as a pool member would do it (assuming you enable port address translation). If they are all on the same VIP then there are several ways to do it, either using a datagroup or a case select (to make it easier to add more in the future), something like:

when HTTP_REQUEST {

switch -glob [string tolower [HTTP::host]] {

    "siteex1.com" {
        node 172.16.46.32 8080
    }
    "siteex2.com" {
        node 172.16.40.253 8081
    }
    "siteex3.com" {
        node 172.16.40.201 8082
    }
}

}