EventHeaders

EventHeaders is a generic term used in event-driven architectures to refer to the metadata associated with an event, separate from the event payload. They accompany events as they move between producers and consumers, enabling routing, filtering, correlation, and auditing. Headers are typically key-value pairs and may be serialized in headers, message envelopes, or storefronts depending on transport.

Typical fields include: type (event type or name), source (originating system or component), timestamp (when produced), id or eventId, correlationId (linking related events), causationId (the triggering event), contentType (MIME type of payload), schemaVersion, dataLocale, trace context. Some systems also include retryCount, deadline, or priority.

Relationship to standards: CloudEvents defines a standardized set of attributes for event metadata, and many message brokers expose headers that play a similar role. EventHeaders can be implemented as a separate header map in HTTP, as per Kafka headers, or as a nested envelope in various protocols.

Usage and design: Keep headers small and immutable once published, avoid sensitive data, and version headers to maintain compatibility. They should be opaque to the payload consumer if not needed by the business logic, but provide enough information to route, monitor, and troubleshoot.

Variants and examples: In HTTP, headers like ce-type, ce-source, ce-id (CloudEvents style). In messaging systems, headers may include equivalents of eventId, timestamp, and correlationId. EventHeaders are a practical construct in many event-driven platforms, serving as a lightweight metadata layer.