A deep dive into Kafka SASL authentication mechanisms — PLAIN and SCRAM — focusing on how different login modules (PlainLoginModule, ScramLoginModule, FileBasedLoginModule) handle credential storage and whether they support hot-reload without broker restarts. SCRAM stores credentials in cluster metadata (KRaft), enabling native hot-reload via Admin APIs. Static JAAS PLAIN requires broker restarts for credential changes, while file-backed PLAIN modules support hot-reload through periodic file watching. The post includes a concrete three-listener broker configuration example, scenario-based comparisons of each mechanism's behavior during credential updates, and production recommendations for zero-downtime credential rotation.
Table of contents
SASL PLAIN and SCRAM in Kafka: The “What”Why “Hot-Reload” Matters for AuthenticationThe Three Login Modules: Plain, SCRAM, and File-BasedA Concrete Example: Three Listeners, Three BehaviorsScenarios: How Each Auth Path Handles ChangesOperational RecommendationsCall to Action363 Impressions