Understanding the Differences Between Older Kafka Versions and Kafka 4.0 — And How to Upgrade Smoothly
Apache Kafka has been a game-changer in the world of real-time data streaming for years. But with the release of Kafka 4.0, there are some big changes that everyone should know about—especially if you’re running older versions. Whether you’re a developer, a DevOps engineer, or a tech enthusiast, this blog will break down what’s new, what’s gone, and how to prepare your Kafka cluster for the upgrade.
What’s New in Kafka 4.0? The Big Picture
Kafka 4.0 isn’t just another update; it’s a major milestone. The biggest headline is that Kafka no longer uses ZooKeeper for managing cluster metadata and coordination. This is a huge architectural change that simplifies Kafka’s operation but also means the upgrade path requires some planning.
Let’s walk through the main differences between older Kafka versions (like 2.x or 3.x) and Kafka 4.0 in simple terms.
1. Goodbye ZooKeeper, Hello KRaft!
Older Versions:
Kafka used ZooKeeper as a separate system to keep track of cluster metadata — things like which brokers are alive, topic configurations, and partition leadership. This meant you had to run and manage a ZooKeeper ensemble alongside your Kafka brokers.
Kafka 4.0:
ZooKeeper is completely removed. Kafka now uses a built-in consensus system called KRaft (Kafka Raft Metadata mode) to handle all metadata internally. This means fewer moving parts, easier setup, and faster cluster management.
Why it matters:
No more ZooKeeper means less complexity and fewer components to maintain. But it also means you can’t just upgrade Kafka and keep ZooKeeper running—you need to migrate your cluster metadata to KRaft first.
2. Smarter Consumer Rebalancing
Older Versions:
When Kafka consumers (applications that read data) join or leave a group, Kafka pauses message consumption during rebalancing. This could cause noticeable delays or downtime, especially in large clusters.
Kafka 4.0:
Introduces a new consumer group protocol (called KIP-848) that makes rebalancing faster and less disruptive. Consumers can continue processing most partitions even while the group is rebalancing.
Why it matters:
Your streaming applications will experience fewer interruptions and better performance during scaling or recovery events.
3. Updated Java Requirements
Older Versions:
Kafka brokers and clients supported Java 8 and Java 11, which were the industry standards for many years.
Kafka 4.0:
Requires Java 17 for brokers, Connect, and tools, and Java 11 for clients and Kafka Streams applications.
Why it matters:
You’ll need to upgrade your Java runtime environments before moving to Kafka 4.0. This may require coordination with your infrastructure or development teams.
4. MirrorMaker 1 Is Gone
Older Versions:
MirrorMaker 1 was a basic tool for replicating data between Kafka clusters.
Kafka 4.0:
MirrorMaker 1 has been removed. Only MirrorMaker 2 remains, which is more robust, scalable, and easier to manage.
Why it matters:
If you’re still using MirrorMaker 1, you’ll need to migrate to MirrorMaker 2 before upgrading.
5. Logging Changes
Older Versions:
Kafka used Log4j for logging.
Kafka 4.0:
Kafka has fully switched to Log4j2, which is more secure and modern.
Why it matters:
You may need to update your logging configurations and tools.
6. API Clean-Up
Kafka 4.0 removes APIs that have been deprecated for over a year. This helps keep the codebase clean and encourages users to adopt the latest, supported features.
7. Early Access to Queues for Kafka
Kafka traditionally uses a publish-subscribe messaging model. Kafka 4.0 introduces early access to queue semantics (via KIP-932), enabling point-to-point messaging patterns.
This is exciting for use cases that require strict message ordering and processing guarantees.
How to Upgrade to Kafka 4.0: A Step-by-Step Guide
Upgrading to Kafka 4.0 isn’t as simple as flipping a switch—especially because of the ZooKeeper removal. Here’s a clear, step-by-step approach to make your upgrade smooth and safe.
Step 1: Check Your Current Setup and Prepare
Know your Kafka version: If you’re running anything older than 3.9.x, you’ll first need to upgrade to 3.9.x before moving to 4.0.
Check Java versions: Make sure your brokers and clients can run on the required Java versions (Java 17 for brokers, Java 11 for clients).
Backup everything: Always back up your Kafka data, configurations, and metadata before starting the upgrade.
Test in a staging environment: Don’t upgrade your production cluster first. Run tests on a staging or dev cluster.
Step 2: Upgrade to Kafka 3.9.x (The Bridge Version)
Kafka 3.9.x supports both ZooKeeper and KRaft modes and includes tools to migrate metadata from ZooKeeper to KRaft.
Upgrade your brokers to 3.9.x.
Make sure everything is stable and running as expected.
Start planning your migration to KRaft.
Step 3: Migrate from ZooKeeper to KRaft
This is the most critical step.
Use Kafka’s official migration tools and follow the detailed migration guide.
The migration process moves all cluster metadata from ZooKeeper into Kafka’s internal KRaft quorum.
Validate that your cluster is healthy and all topics, partitions, and configurations are intact after migration.
Step 4: Upgrade to Kafka 4.0
Once your cluster is running in KRaft mode on 3.9.x:
Upgrade your brokers to Kafka 4.0.
Upgrade clients and tools, making sure they’re compatible with Kafka 4.0 and the new Java versions.
Monitor your cluster closely for any issues.
Step 5: Post-Upgrade Cleanup and Optimization
Remove any deprecated APIs or features.
Switch from MirrorMaker 1 to MirrorMaker 2 if you haven’t already.
Update your logging configurations to use Log4j2.
Explore new features like improved consumer rebalancing and queue semantics.
Final Thoughts
Kafka 4.0 is a powerful, modernized release that simplifies cluster management and boosts performance. But because it removes ZooKeeper and updates core dependencies, it requires a thoughtful upgrade plan.
By following the steps above—starting with upgrading to Kafka 3.9.x, migrating to KRaft, and then moving to Kafka 4.0—you’ll ensure a smooth transition with minimal downtime.
If you’re running Kafka in production, don’t rush the upgrade. Test thoroughly, involve your teams, and take advantage of Kafka’s detailed documentation and tools.
Kafka 4.0 is the future of streaming platforms—embrace it to unlock new possibilities and keep your data pipelines running smoothly!
Have you started your Kafka 4.0 upgrade? Feel free to share your experiences or ask questions in the comments below!
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