Kafka Connect

Connect Overview

At its core, connect is about doing one thing well inside your Apache Kafka project. Once you understand the pattern, you can apply it consistently across features and teams.

Good connect pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

// consume, transform, and re-produce (a simple stream stage)
await consumer.run({
  eachMessage: async ({ message }) => {
    const event = JSON.parse(message.value.toString());
    const enriched = { ...event, receivedAt: Date.now() };
    await producer.send({
      topic: 'orders-enriched',
      messages: [{ key: event.id, value: JSON.stringify(enriched) }],
    });
  },
});

Stream processing consumes from one topic, transforms events, and produces to another.

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

Apache Kafka Cheatsheet

Handy KafkaJS reference related to connect.

How Connect Works in Apache Kafka

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

Stream processing consumes from one topic, transforms events, and produces to another.

• 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 Connect

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

Common Mistakes

• Skipping error handling and edge cases when wiring up connect.
• Leaving connect untested, so regressions slip into production.
• Over-engineering connect before you actually need the extra flexibility.
• Ignoring documentation, which makes connect hard for the next developer to change.

Key Takeaways

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