We are using the mirror maker to sync on-premise and AWS Kafka topics. How can a topic with its schema registered in on-premise be replicated exactly the same in other clusters (AWS in this case)? How Avro schema is replicated using mirror maker?
MirrorMaker only copies byte arrays, not schemas. And doesn't care about the format of the data
As of Confluent 4.x or later, Schema Registry added endpoint GET /schemas/ids/(number). So, if your consumers are configured to the original registry, this shouldn't matter since your destination consumers can lookup the schema ID.
You otherwise can mirror the _schemas topic as well, as recommend by Confluent when using Confluent Replicator
If you absolutely need one-to-one schema copying, you would need to implement a MessageHandler interface, and pass this on to the MirrorMaker command, to get and post the schema, similar to the internal logic I added to this Kafka Connect plugin (which you could use Connect instead of MirrorMaker). https://github.com/OneCricketeer/schema-registry-transfer-smt