supporting a http2 sni website with f5 ltm?

So the problem is only that ur sending app.external.com to your node but you have this hostname not configured and your node only listen to server.internal.com? So a simple Hostname Header rewrite is enough? Then create a LTM Policy with when host is app.external.com rewrite to server.internal.com 

iRule for logging? something like this 

when HTTP_REQUEST_RELEASE {
   log local0. "Client [IP::client_addr] This is the HTTP Host [HTTP::host]"
   log local0. "Query string of URI: [HTTP::uri] is [URI::query [HTTP::uri]]"
}