Structured Logging

In this lesson you will learn structured logging in Apache Kafka, why it matters within observability, and how to use it correctly with clear, copy-ready examples.

Structured Logging Overview

Structured Logging is a building block you will reach for often in Apache Kafka. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn structured logging properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real Apache Kafka projects.

import { Kafka, logLevel } from 'kafkajs';

const kafka = new Kafka({
  clientId: 'my-app',
  brokers: ['localhost:9092'],
  logLevel: logLevel.INFO,
});

// create producers, consumers, or an admin client from `kafka`

Every KafkaJS app starts from a Kafka client configured with a clientId and broker list.

Structured Logging Example

import { Kafka } from 'kafkajs';

const kafka = new Kafka({ clientId: 'app', brokers: ['localhost:9092'] });
const producer = kafka.producer();
const consumer = kafka.consumer({ groupId: 'group' });

Start from a minimal Structured Logging example and grow it only as needed.
Keep configuration explicit so Structured Logging behaves the same in every environment.
Name things clearly so teammates understand your Structured Logging at a glance.
Add tests around Structured Logging early to lock in expected behaviour.

Apache Kafka Cheatsheet

Handy KafkaJS reference related to structured logging.

Task	Example	Purpose
Create client	`new Kafka({ clientId, brokers })`	Connect to the cluster
Produce	`producer.send({ topic, messages })`	Publish events
Consume	`consumer.run({ eachMessage })`	Process events
Subscribe	`consumer.subscribe({ topic })`	Choose topics to read
Group	`kafka.consumer({ groupId })`	Scale consumers
Admin	`admin.createTopics(...)`	Manage topics
Commit offset	auto-commit or `commitOffsets`	Track progress

How Structured Logging Works in Apache Kafka

Structured Logging builds on Kafka's log-based design, where producers append events to partitioned topics and consumer groups read them independently, tracking their own offsets.

Every KafkaJS app starts from a Kafka client configured with a clientId and broker list.

Topics are split into partitions for parallelism and ordering per key.
Producers choose a partition, usually by message key.
Consumer groups share partitions so work scales horizontally.
Offsets record how far each group has read.

Practical Guidance for Structured Logging

In production, structured logging needs attention to delivery guarantees, retries, and observability. Make handlers idempotent and monitor consumer lag closely.

Concern	Recommendation
Ordering	Key related events so they land on one partition
Reliability	Use acks=all and idempotent producers
Idempotency	Handle duplicate deliveries safely
Monitoring	Track consumer lag and error rates

Common Mistakes

Copying structured logging snippets without understanding what each line does.
Skipping error handling and edge cases when wiring up structured logging.
Leaving structured logging untested, so regressions slip into production.
Over-engineering structured logging before you actually need the extra flexibility.

Key Takeaways

Structured Logging is a core part of working effectively with Apache Kafka.
Start small and keep structured logging focused on a single responsibility.
Apply consistent patterns so structured logging scales across your project.
Test and document structured logging to keep it maintainable over time.

Pro Tip

Pair structured logging with automated tests from day one. It is far cheaper to catch Apache Kafka regressions in CI than in production.