The Apache Kafka ecosystem is undergoing its most significant architectural evolution: the transition from ZooKeeper to KRaft (Kafka Raft Metadata mode). By integrating a native Raft-based consensus system directly into Kafka, the platform eliminates the complexity of external coordination, resulting in a more scalable, resilient, and operationally streamlined architecture.
Confluent Platform supports this transition through three primary pathways: Manual Migration, Ansible Automation, and Confluent for Kubernetes (CFK). This guide explores the three-state journey to KRaft and the critical considerations for a successful cutover.
Why the Move to KRaft?
The shift to KRaft is a fundamental requirement for the future of Kafka.
- System Consolidation: Metadata management moves into Kafka itself, removing the “double-management” overhead of a separate ZooKeeper ensemble.
- Enhanced Scalability: KRaft supports higher partition counts and faster recovery times by eliminating the metadata loading bottleneck.
- Operational Simplicity: A unified security model and a single set of monitoring tools simplify the infrastructure stack.
- Deprecation Timeline: ZooKeeper is officially deprecated. Migration is a prerequisite for upgrading to the latest Confluent Platform versions.
The 3 States of Migration
Regardless of the tool you use, the journey follows three distinct operational states. This phased approach ensures data integrity and allows for validation before the final cutover.
| State | Mode | Operational Reality |
| State 1 | ZooKeeper Mode | The Baseline: The cluster operates traditionally. ZooKeeper handles all metadata (leader elections, configs, and ACLs). Brokers are unaware of KRaft. |
| State 2 | Dual-Write Mode | The Bridge: KRaft Controllers are active. Metadata is synchronized between ZooKeeper and KRaft in real-time. This is the last point where a rollback is possible. |
| State 3 | KRaft-Only Mode | The Destination: Migration is finalized. ZooKeeper is decommissioned. The cluster is now simpler and faster. Rollback is no longer possible. |
Choosing Your Migration Path
1. Manual Migration (Classic Approach)
Manual migration offers the most granular control. It is best suited for administrators who need to manage every step of the process without relying on external automation frameworks.
- How it works: You manually retrieve the Cluster ID from ZooKeeper, format the new KRaft controller storage, and perform a rolling restart of all brokers with migration properties enabled.
- Best For: Small clusters or environments where automation tools are not permitted.
- The Trade-off: Higher risk of human error and manual configuration mismatches.
2. Automated Migration with Confluent Ansible
If you manage Kafka on Virtual Machines or Bare Metal, Confluent Ansible provides a repeatable, “declarative” workflow.
- How it works: You update your inventory with a migration flag and run dedicated playbooks. Ansible handles the logic of fetching the Cluster ID, deploying controllers, and sequencing the rolling restarts of the brokers.
- Best For: Enterprise fleets where consistency and speed across multiple environments are critical.
- The Trade-off: Requires an established Ansible infrastructure and expertise.
3. Kubernetes-Native Migration with CFK
For organizations running on Kubernetes, Confluent for Kubernetes (CFK) provides a fully orchestrated, cloud-native experience.
- How it works: You deploy a KRaftMigrationJob Custom Resource. The CFK operator then takes over, managing the state transitions from Dual-Write to Finalization automatically while monitoring the health of your pods.
- Best For: GitOps-driven environments and teams already using the CFK operator.
- The Trade-off: Restricted to the CFK ecosystem.
The “One-Way Door”: What You Must Know
Migration is a high-stakes operation. Adhering to these rules is non-negotiable.
1. The Point of No Return
Once you move from State 2 (Dual-Write) to State 3 (KRaft-Only), you have crossed a “one-way door.” Brokers stop writing to ZooKeeper entirely. You can never roll back to ZooKeeper after finalization. Any failure after this point requires a brand-new cluster build.
2. Never “First Time” in Production
Practice the full 3-state transition in a staging or QA environment that mirrors your production security (TLS/SASL) and data volume.
3. Backups are Non-Negotiable
Before moving to State 2, take full backups of ZooKeeper data directories, broker configurations, and broker log directories. These are your only safety nets if State 2 fails.
4. Cluster ID Integrity
KRaft controllers must be formatted with the exact same Cluster ID used by your current ZooKeeper ensemble. A mismatch will cause brokers to reject the new controllers, leading to a split-brain scenario or total downtime.
5. Don’t Mix Upgrade and Migration
First, upgrade your Confluent Platform to a version that supports KRaft migration (7.7.x is recommended). Stabilize the cluster. Then, and only then, initiate the migration to KRaft.
Conclusion
Migrating to KRaft is more than just a version update; it is a foundational transformation of your data infrastructure. Whether you choose the control of a Manual approach, the scalability of Ansible, or the orchestration of CFK, the goal is a leaner, faster Kafka.
Plan carefully, validate thoroughly in the Dual-Write state, and only close the “One-Way Door” when you are 100% confident in your new KRaft quorum.
Ready to Seamlessly Migrate to KRaft?
If you are planning the critical shift from ZooKeeper to KRaft and want to ensure a zero-downtime transition, Alephys is here to guide your journey.
Navigating the “One-Way Door” requires precision. Whether you are validating Dual-Write performance, managing complex Ansible workflows, or orchestrating a Kubernetes-native cutover with CFK, our team of data experts ensures your infrastructure remains resilient. We help you eliminate the risks of split-brain scenarios and data loss so you can unlock the full scalability of a controller-less architecture with confidence.
Author: Siva Munaga, Solution Architect at Alephys.
Gireesh Krishna Paupuleti, Solution Architect at Alephys.
I specialize in building scalable data infrastructure and executing complex Kafka migrations that modernize enterprise platforms. Let’s connect on LinkedIn to discuss your move to KRaft and your long-term infrastructure goals!