you can solve this by setting expresion value to instance-id attribute, that enables you to reference any system property.
will set instance-id to value of "sysprop.server" system property.
properties itself can be defined inside host.xml
analogous, we use
so no additional property is required and you can see in mod_jk status 'who is who' ...
Thanks everyone for fast and comprehensive answers; it works;
for the records: we've just added the ability to specify the instance-id through the web cnsole. it will be included with the console 1.3.0 (>=7.1.2)