When upgrading to OpenNMS Horizon 30, you may find that even after following standard upgrade procedures it will produce a HTTP/503 for you. Meaning Jetty started but… Karaf is dead. This appears to be another *finger guns* gotcha by the OpenNMS team for the non-paid product.

You must MANUALLY update your config.properties file in opennms/etc to update the reference for Felix that was upgraded from 6.0.4 to 6.0.5;

config.properties:karaf.framework.felix=mvn\:org.apache.felix/org.apache.felix.framework/6.0.4

to

config.properties:karaf.framework.felix=mvn\:org.apache.felix/org.apache.felix.framework/6.0.5