I finally found the reason for the error I was getting. Approach #2 is actually as simple as written above, binding to the same address(es) but different ports does work. But there is of course more than one place in which you can specify ports that an instance should use. I had a remote debugging port specified in the JVM parameters under [JBOSS_HOME]/bin/standalone.conf. I changed this port as well in the second instance, and now it starts smoothly.