When shading Drools jars into an uber-jar (packing project dependencies into one final project jar), a META-INF/kie.conf file needs to be created in the resouces folder of the uber-jar. This file contains references to Drools service classes (like KieServices).

We have a new component in Drools that loads and handles service classes, called ServiceRegistry. This registry needs a kie.conf file so it knows which class it should load for each specific service. For normal kjars, no custom kie.conf file is needed, because the Drools jars are not packed into an uber-jar, so kie.conf is at its proper location (it is in each Drools jar). However when packed in an uber-jar, there is no META-INF/kie.conf file in the resources folder of the uber-jar, which is the location ServiceRegistry searches for this conf file.