What is a dead letter queue (DLT) in Kafka?

A dead letter queue (dead letter topic, DLT) is a topic that receives records that could not be processed, so one bad record does not block the rest. Plain Kafka consumers have no built-in DLQ; it is a pattern you or a framework implement. Apache Kafka components that support it: for Kafka Connect sink connectors, set errors.tolerance=all and errors.deadletterqueue.topic.name; errors.deadletterqueue.context.headers.enable=true adds headers (prefixed __connect.errors.) describing the error. In Kafka Streams, errors.dead.letter.queue.topic.name makes the default exception handler send a dead letter record to that topic. In Spring for Apache Kafka (reference 4.1.1), DeadLetterPublishingRecoverer used with DefaultErrorHandler publishes the failed record, after the configured retries, to a topic named <original>-dlt by default, in the same partition, with headers carrying the exception and the original topic, partition and offset.

Expected key concepts: dead letter topic, DLT, DLQ, errors.tolerance, errors.deadletterqueue.topic.name, errors.dead.letter.queue.topic.name, DeadLetterPublishingRecoverer, DefaultErrorHandler, headers, retries