Apache Flink vs Kafka Streams

Apache Flink is a free, self-hosted framework and distributed processing engine for stateful computations over unbounded and bounded data streams. It supports event-driven applications, stream and batch analytics, and data pipelines and ETL. Listed correctness features include exactly-once state consistency, event-time processing and late-data handling. APIs include SQL for stream and batch data, DataStream and ProcessFunction for time and state. Operational capabilities cover flexible deployment, high availability, savepoints, scale-out architecture, very large state and incremental checkpoints. The project lists low latency, high throughput and in-memory computing. Flink runs in common cluster environments; for Kubernetes, the Kubernetes Operator is identified as the standard deployment mechanism. Connectors include AWS, Cassandra, Elasticsearch, Google Cloud PubSub, HBase, Hive, JDBC, Kafka, MongoDB, OpenSearch, Prometheus, Pulsar and RabbitMQ. Security requires configuration because SSL/TLS, REST authentication and SQL Gateway authentication are disabled by default. It is available at free under Apache License v2.

Kafka Streams is a free client library for building applications and microservices that use data stored in Kafka clusters. It processes Kafka data with event-time handling, windowing, and real-time queries of application state. The Streams DSL provides operations such as mapping, filtering, joins, and aggregations, while the Processor API supports custom processors and state stores. Fault-tolerant local state supports stateful work such as windowed joins and aggregations, and the library offers exactly-once processing semantics. Applications can run on one machine or scale across multiple machines, and can be deployed in containers, virtual machines, on bare metal, or in cloud environments. Kafka Streams uses Kafka as its internal messaging layer and does not require a separate processing cluster. It supports Java and Scala and integrates with Kafka security features for encryption in transit, client authentication, and authorization. The software is licensed under Apache License 2.0. The Apache Software Foundation says it does not sell its software or provide formal or commercial support for its packages; project communication is available through community mailing lists.