The Avro Gateway is a little API in front of a Schema Registry. It ensure that all the consumers/producers schemas are compatible between them inside a topic. It keeps track of all the schema versions used by the clients and refuse to serve any schema versions susceptible to breaking the current clients.
You have a Kafka topic which is consumed by some other teams and you want to upgrade the Avro schema for you producer. How do you ensure not to break the consumers with a breaking change into you schema? Which consumer should you upgrade before?
You need to consume a Kafka topic managed by an another team. How do you ensure that you current Avro schema version will be able to decode the messages? Which version should you use? How do you prevent the producer team to make a schema change not handled by your consumer?
The Avro Gateway aims to resolve those issues.