Kafka Streams

A lightweight Java library for building distributed, fault-tolerant stream processing applications directly on top of Apache Kafka.

Kafka Streams eliminates the need for separate processing clusters by running as a standard library within your JVM application. It handles core stream processing requirements: stateful aggregations (windowed joins), exactly-once semantics (EOS), and event-time processing using internal Kafka topics for fault tolerance. By leveraging RocksDB for local state storage and Kafka consumer groups for scalability, it enables developers to build microservices that process millions of events per second with millisecond latency.

https://kafka.apache.org/documentation/streams/