When the user uses fabric to generate Active MQ clusters, fabric assigns free ports to these brokers and it is hard to configure serverURL without using discovery. But when you set the following
<config-property name="ServerUrl">
discovery:(fabric:a-mq-east)
</config-property>
It will fail due to missing zookeeper and fabric libraries.

17:09:30,326 ERROR [org.apache.activemq.ra.ActiveMQEndpointWorker] (default-threads - 1) Failed to connect to broker [discovery:(fabric:a-mq-east)]: Could not create Transport. Reason: java.io.IOException: DiscoveryAgent scheme NOT recognized: [fabric]:

javax.jms.JMSException: Could not create Transport. Reason: java.io.IOException: DiscoveryAgent scheme NOT recognized: [fabric]