One Apache is listening to port 80 and handling lots of
virtual hosts via mod_proxy and ReWriteRules to the other
instances running on ports like 13000, 13100, 13200, …
All of them work fine, the only problem are the PERL Modules.
When I installed rt 3.0.4 the CPAN module HTML:Mason was
updated to 1.20 so our rt 2.0.x were not running anymore
because they need HTML:Mason 1.05.
We had to downgrade the Parser Module to get everything back.