Apache Flink vs Esper

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.

Esper is a language, compiler, and runtime for complex event processing and streaming analytics in Java and .NET. Its Event Processing Language extends SQL with expressions over events and time. The compiler turns EPL into bytecode that can be packaged in JAR files. Esper and NEsper embed inside Java or .NET processes rather than running as standalone servers. The in-memory runtime is described as memory-efficient and low-latency and does not require external storage or services. Adapters handle CSV, JMS, HTTP, Kafka, database, and socket input and output, with JMX metrics exposure. Queries can join event streams with web services and relational databases through SQL-query or method-invocation joins. Esper Enterprise Edition adds scale-out architecture with elastic scaling, load balancing, fault tolerance, and multi-datacenter support using Apache Kafka and Apache Zookeeper. Listed uses include business-process monitoring, financial applications such as fraud detection, network and application monitoring, and sensor networks. Esper 9.0.0 is listed under GNU GPL (GPL v2); commercial redistribution licenses are available. Production support has Bronze, Silver, and Gold levels, plus a Developer Seat for how-to questions.