Blog

Engineering notes from a visual Kafka Streams builder: client-library traps, testing stories, and the reasoning behind design decisions. RSS.

• The compiler was never what you wanted 3 Sept 2026

  Reading an Avro topic from Kafka Streams in Java is seven steps, and five of them run again every time you need a field somebody added. What that buys is a compiler — and a compiler answers a narrower question than the one you actually have.

• SpEL in Kafka Streams: from evaluator to editor 31 Aug 2026

  Spring's SpEL tokenizer is package-private. What it takes to build an editor on an evaluator: highlighting, completions, and errors a user can act on.

• Kafka Streams topologies you can draw and run 19 Aug 2026

  A Kafka Streams diagram shows the shape but not the logic. What changes when you draw the topology with the expressions inside, checked on real records.

• KafkaStreams.state() says REBALANCING. Every thread is dead. 2 Aug 2026

  A Kafka Streams client whose processing threads have all died keeps reporting REBALANCING — forever. Why it happens, how to detect it, and what any tool showing raw state() should do instead.