public Set<String> clusters() {
        return new HashSet<>(getList(CLUSTERS_CONFIG));
    }
Top-level config describing replication flows between multiple Kafka clusters.
 <p>
 Supports cluster-level properties of the form cluster.x.y.z, and replication-level
 properties of the form source->target.x.y.z.
 e.g.

<pre>
     clusters = A, B, C
     A.bootstrap.servers = aaa:9092
     A.security.protocol = SSL
     --->%---
     A->B.enabled = true
     A->B.producer.client.id = "A-B-producer"
     --->%---
</pre>
connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorMakerConfig.java