How do you handle Kafka message patterns and access message headers and partition info via KafkaContext in NestJS?

Q: How do you handle Kafka message patterns and access message headers and partition info via KafkaContext in NestJS?

// Handler — access Kafka metadata via KafkaContext @MessagePattern('order-events') async handleOrderEvent( @Payload() message: KafkaMessage, @Ctx() ctx: KafkaContext, ): Promise { const topic = ctx.getTopic(); const partition = ctx.getPartition(); const offset = ctx.getMessage().offset; const headers = ctx.getMessage().headers; const correlationId = headers?.['x-correlation-id']?.toString(); console.log(`Topic: ${topic}, Partition: ${partition}, Offset: ${offset}`); await this.processEvent(message.value); } // Publisher — send with key and headers async publishOrderCreated(order: Order): Promise { const message = { key: order.id.toString(), // key determines partition — ensures ordering per order value: order, headers: { 'x-correlation-id': randomUUID(), 'x-source-service': 'orders-service', }, }; this.client.emit('order-events', message).subscribe(); } Message key determines which partition receives the message — same key always goes to the same partition. All messages with the same key are ordered within their partition — critical for event sourcing. Without a key, Kafka round-robins across partitions — no ordering guarantee. Offset identifies the message position within a partition — use it for manual offset commits. Headers are available via ctx.getMessage().headers — use for correlation IDs and trace context propagation.

Difficulty: 5/10

KafkaContext, message headers, partition handling

@MessagePattern maps to a Kafka topic name. Use @Ctx() to inject a KafkaContext which exposes getTopic(), getPartition(), and getMessage() containing the offset and headers. Publish messages with a key to determine partition assignment and include headers for cross-cutting concerns like correlation IDs.

KafkaContext metadata access and keyed message publishing

Kafka message key and ordering guarantees:

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Message key determines which partition receives the message — same key always goes to the same partition.
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How do you handle Kafka message patterns and access message headers and partition info via KafkaContext in NestJS?

Scenario Questions

Follow-up Questions