To use a shared Kafka cluster across multiple independent OpenNMS environments, you must set the "org.opennms.instance.id" property in OpenNMS and its Minions to guarantee unique Topic names in Kafka.
Then the confd based configuration was introduced, that property was supposed to be available via the YAML file:
Unfortunately, that is not working. It is ignored by the Minion when passed that property via the YAML file, and the default prefix is used.
The workaround is passing custom.properties (or custom.system.properties) via volume mount.