I have a servlet
(parent) that needs to invoke another servlet (child) that resides on the same appserver (Could be Tomcat
, Websphere or Weblogic). The way we build the URL now to reach the child servlet is to build the URL up by pulling the protocol, host and port out of the request object when the parent servlet executes. Since the child is on the same appserver, we use the same host/port and protocol. The host is always going to be local, so we could just use localhost instead of a getHost() call.
This code works fine, but some clients have started to use a load balancer and if the LB is not configured to pass through the client's address in the request object, what happens is we wind up getting back the IP/port of the LB instead of the app server and our servlet request will fail.
As a solution, we could change to use "localhost" instead of calling srcURL.getHost(), however how would we resolve the port? For instance, the port Tomcat is listening on is not guaranteed to be 8080 and can be changed by the user (same with other appservers). Is there a way to dynamically determine what port the app server is using without requiring the user to have to tell the servlet or by getting it out of the request object?