Kafka headers are optional key-value pairs of metadata attached to each record, next to its key and value. Use them for information about a message that should not live inside the payload.
Common uses:
- Routing, where consumers route messages based on a header.
- Tracing, where a correlation ID follows a request across services.
- Security context, such as an authentication token.
- Content metadata, such as the MIME type or encoding.
- Source identification, naming the origin system.
// Producer adding headers
ProducerRecord<String, String> record = new ProducerRecord<>(
"my-topic", "key", "value");
record.headers().add("correlation-id", "12345".getBytes());
record.headers().add("source-system", "order-service".getBytes());
Headers do not affect partitioning, and they add metadata without changing the message payload.
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