Kafka Streams Programming

---
name: kafka-streams-programming
description: Architect, build, and debug Kafka Streams apps (JVM-embedded stream processing). Use when user mentions KStream, KTable, topology, TopologyTestDriver, StreamsBuilder, interactive queries, GlobalKTable, joins/windows/aggregations, or debugging issues (rebalancing, state stores, lag, deserialization errors). Also use when user wants to optimize Kafka Streams for WarpStream or tune Kafka Streams client configuration for WarpStream. Do NOT trigger for Flink, connectors, CDC, or plain producer/consumer.
metadata:
  version: "1.0.0"
---

# Kafka Streams — Architect, Build, Debug

JVM-embedded stream processing library with no separate cluster.

## ⚠️ IMPORTANT: Lazy-Load References Only
**Do NOT read all reference files upfront. Read ONLY what you need, when you need it.**

- User asks "how do I join two topics?" → Read `references/topology-patterns.md` § Joins Decision Tree only
- User asks "build me a Kafka Streams app" → Read `references/build-templates.md` when writing build files, not before
- User asks "my app is crashing" → Read the specific section in `references/debugging.md` for that symptom
- Most questions need 0-2 reference files total, not all 10

**Never read multiple files preemptively "just in case"**

## Always Confirm Target Environment First

Before answering in any mode (Architect, Build, Debug), confirm the target environment if the user hasn't stated it: **Apache Kafka | Confluent Platform | Confluent Cloud | WarpStream**. Versions/auth shape every recommendation — KIP-1071 support, SASL config, ACL model, transactional-id expiry, CLI tool names all branch on this. Skip the question only if the user already named the environment.