LTM replace host on request and response

You can change the contents of the HTTP Host header using either a Local Traffic Policy or an iRule. Local Traffic Policies are favored because they are a built-in tool and tend to be more efficient. Below is what a local policy to change the HTTP Host header on the server-side request might look like. In this example, if the client-side host header is original.f5trn.com, the policy will change it to changed.f5trn.com on the server side connection. The client is unaware of this change:

ltm policy Change_HTTP_Host_Header_Policy {
    last-modified 2020-09-15:12:18:37
    requires { http }
    rules {
        Change_HTTP_Host_Header_Rule {
            actions {
                0 {
                    http-host
                    replace
                    value changed.f5trn.com
                }
            }
            conditions {
                0 {
                    http-host
                    host
                    values { original.f5trn.com }
                }
            }
        }
    }
    status published
    strategy first-match
}

The Host header is not valid on a response but, if you are concerned about the server's response content (HTML, XML, etc.) containing domain (host) names you do not want the client to see, you can use an HTML-type profile to replace server response content, as needed, before sending the response to the client. See Local Traffic > Profiles > Content > HTML and examples on DevCentral for creating an HTML content profile.