Correlation id

As explained in Kafka for Architects

A correlation ID is an identifier carried with related request and response messages so they can be matched.

In request-response messaging, a correlation ID is a shared identifier that lets a service match a reply to its request. In Kafka, it is commonly carried in a message header and echoed in the response. section 7.1.2

Matching messages is only part of the design: the response must also reach the service instance that holds the request context. If a consumer fails and another instance takes over its partition, that instance may lack the context needed to process the reply. RabbitMQ uses the same matching principle with a reply queue and correlation ID. section 7.1.2 section 5.3.1

Figure 7.5 Both services participating in the request-response pattern have a producer and consumer container. The request and response are matched using the correlation ID, specified in the message header.

The diagram shows request and response services matching messages through the correlation ID in their headers. section 7.1.2

How Kafka for Architects covers it

How deep it goes

Defines header-based matching and explains response-routing and lost-context problems, without detailing a complete recovery implementation.

Examples

Uses a CORRELATION_ID header in Kafka services and matching IDs on RabbitMQ request-reply queues.

What you can do after

Understand how a shared identifier pairs a reply with its request and why routing it to the originating service instance matters.

How it connects

Connects request-response messaging with message headers, reply queues, consumer groups, and partition assignment.

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Also explained in

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  Secure APIsA trace ID is an identifier shared by telemetry records belonging to the same request execution or distributed processing path.
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  Go by ExampleA trace ID is an identifier that correlates processing and log records belonging to the same request or distributed operation.
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  gRPC Microservices in GoA trace ID is an identifier that correlates all operations belonging to one distributed request.
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  Cloud Observability in ActionA trace identifier is the identifier shared by spans belonging to one distributed request trace.

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Related concepts

• trajectoryused by · A trajectory is an ordered sequence of states, actions, events, or operations that records or describes progression through successive steps or over time.
• request-response APIused by · A request-response API is an interaction pattern in which a requester sends a request to a provider and receives a corresponding response.
• loguses · A log is a record of events, activity, or diagnostic information produced during the operation of a system or process, often ordered by time.
• spanhas part · A span is a record of an individual operation within a trace, typically including its timing, context, outcome, and relationships to other operations.
• contextuses · In Go, context.Context is an interface carrying cancellation signals, deadlines, and request-scoped values across function and service boundaries.

This explainer was generated by Manning's knowledge graph from the text of Kafka for Architects. The section links point to the parts of the book it draws on.