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Kafka Error `DUPLICATE_BROKER_REGISTRATION`

Error code 101 · Non-retriable Broker

This broker ID is already in use.

Common Causes

Two broker processes were started with the same broker.id — typically from a misconfigured config file or copy-paste error in a new node setup
A broker was restarted and the old process did not fully terminate before the new one attempted to register with the KRaft controller
In cloud environments, a new VM was provisioned with an AMI/image that already had a broker.id baked in, conflicting with an existing running broker

Solutions

Ensure each broker has a unique broker.id (ZooKeeper mode) or node.id (KRaft mode) — audit all broker configs before starting new nodes
Confirm the old broker process has terminated (check PID file and process list) before starting the replacement with the same ID
In KRaft mode, use auto-generated node IDs or a provisioning script that allocates unique IDs from a registry before writing broker config

Diagnostic Commands

# Show KRaft quorum replication details
kafka-metadata-quorum.sh --bootstrap-server localhost:9092 describe --replication | grep -E 'NodeId|Broker'

# Look for duplicate registration events
grep 'DuplicateBrokerRegistration\|already registered\|broker.id' /var/log/kafka/server.log | tail -20

Related APIs

This error can be returned by: BrokerRegistration

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