BrokerHeartbeatManager heartbeatManager() {
        if (heartbeatManager == null) {
            throw new RuntimeException("ClusterControlManager is not active.");
        }
        return heartbeatManager;
    }
Returns true if the broker is active. Active means not fenced nor in controlled
shutdown; Returns false if it is not active or if it does not exist.
metadata/src/main/java/org/apache/kafka/controller/ClusterControlManager.java