RewriteRule. Get the physical port number inside the Apache configuration

Question

2I have following configuration:

---443-> Load-Balancer-1 ---80> Apache-Proxy ---8080> Tomcat
---443-> Load-Balancer-2 ---81> Apache-Proxy ---8081> Tomcat
---443-> Load-Balancer-3 ---82> Apache-Proxy ---8082> Tomcat

There are several entries in the Apache server over different ports 80, 81, 81. There is a Tomcat listening port for every Apache port. Here is the simplified configuration:

  <VirtualHost *:80 *:81 *:82>
     RewriteRule ^/(.*) ://localhost:80<xx>/$1 [P,L]
  </VirtualHost>

In the configuration above instead of <xx> the physical apache port number must be used. In this case 80, 81 or 82.

I tried using %{SERVER_PORT}, but it is never a physical port. If the UseCanonicalName Off, it is the port of the load balancer (443 in my example). If the UseCanonicalName On, it is one of ports configured in the Apache configuration. In my case it always was 82.

UseCanonicalPhysicalPort On|Off directive was theoretically designed to solve this problem, but it seems not to be flexible enough for virtual host configuration.

http://httpd.apache.org/docs/current/mod/core.html#usecanonicalphysicalport

I tried to access CGI variable SERVER_PORT as %{ENV:SERVER_PORT}, but it did not exist.

I tried to workaround the problem using SetEnvIf, but this directive has no access to the port number at all (why?).

Current working solution was creating three different virtual host and hardcode the port number, but I do not like it.