Kafka Bridge Error: Fixing InitProducerIdResponse

Are you encountering issues while trying to produce messages using Kafka Bridge in your Kafka cluster? Specifically, are you seeing the dreaded Unexpected error in InitProducerIdResponse? This article dives into the common causes and solutions for this error, providing a step-by-step guide to troubleshoot and resolve the problem. We will explore the configurations, potential pitfalls, and debugging techniques to get your Kafka Bridge up and running smoothly.

Understanding the Issue

The error message Unexpected error in InitProducerIdResponse; The server experienced an unexpected error when processing the request indicates that the Kafka broker is failing to initialize a producer ID for the Kafka Bridge. This often points to problems with transactional settings, authentication, or broker configurations. Let's break down the error and its potential causes:

2025-11-14 08:41:19 INFO  [kafka-producer-network-thread | producer-12] 
TransactionManager:544 - [Producer clientId=producer-12] 
Transiting to fatal error state due to org.apache.kafka.common.KafkaException: 
Unexpected error in InitProducerIdResponse; The server experienced an unexpected 
error when processing the request.

2025-11-14 08:41:19 ERROR [kafka-producer-network-thread | producer-12] 
Sender:524 - [Producer clientId=producer-12] Aborting producer batches due to fatal error

org.apache.kafka.common.KafkaException: Unexpected error in InitProducerIdResponse; 
The server experienced an unexpected error when processing the request.
    at org.apache.kafka.clients.producer.internals.TransactionManager$InitProducerIdHandler.handleResponse(TransactionManager.java:1525)
    at org.apache.kafka.clients.producer.internals.TransactionManager$TxnRequestHandler.onComplete(TransactionManager.java:1424)
    at org.apache.kafka.clients.ClientResponse.onComplete(ClientResponse.java:154)
    at org.apache.kafka.clients.NetworkClient.completeResponses(NetworkClient.java:669)
    at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:661)
    at org.apache.kafka.clients.producer.internals.Sender.maybeSendAndPollTransactionalRequest(Sender.java:452)
    at org.apache.kafka.clients.producer.internals.Sender.runOnce(Sender.java:328)
    at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:242)
    at java.lang.Thread.run(Thread.java:840)

2025-11-14 08:41:19 ERROR [kafka-producer-network-thread | producer-12] 
HttpSourceBridgeEndpoint:171 - Failed to deliver record ProducerRecord(
    topic=onprem.utv.test-data.add.v1,
    partition=0,
    headers=RecordHeaders(headers = [], isReadOnly = true),
    key=[B@5874f2df,
    value=[B@3c25d70a,
    timestamp=null
)

org.apache.kafka.common.KafkaException: Unexpected error in InitProducerIdResponse; 
The server experienced an unexpected error when processing the request.
    at org.apache.kafka.clients.producer.internals.TransactionManager$InitProducerIdHandler.handleResponse(TransactionManager.java:1525)
    at org.apache.kafka.clients.producer.internals.TransactionManager$TxnRequestHandler.onComplete(TransactionManager.java:1424)
    at org.apache.kafka.clients.ClientResponse.onComplete(ClientResponse.java:154)
    at org.apache.kafka.clients.NetworkClient.completeResponses(NetworkClient.java:669)
    at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:661)
    at org.apache.kafka.clients.producer.internals.Sender.maybeSendAndPollTransactionalRequest(Sender.java:452)
    at org.apache.kafka.clients.producer.internals.Sender.runOnce(Sender.java:328)
    at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:242)
    at java.lang.Thread.run(Thread.java:840)

This error generally arises when the Kafka producer, in this case the Kafka Bridge, fails to initialize its producer ID with the Kafka brokers. This initialization is crucial for ensuring idempotent and transactional message delivery. Let's explore the common causes and solutions to resolve this issue effectively.

Configuration Review: Kafka Bridge and Kafka Resources

To effectively troubleshoot this error, examining the configurations of both the Kafka Bridge and the Kafka cluster is essential. Here’s a detailed look at the provided configurations and potential areas for adjustment.

Kafka Bridge Configuration

This is the configuration for your Kafka Bridge resource, defined using the Strimzi operator. Let's examine it:

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaBridge
metadata:
  name: kafka-bridge
  namespace: kafka
spec:
  authentication:
    audience: kafka
    clientId: kafka-bridge
    clientSecret:
      key: secret
      secretName: kafka-bridge-oauth-secret
    grantType: urn:ietf:params:oauth:grant-type:uma-ticket
    tokenEndpointUri: http://keycloak.keycloak.svc.cluster.local:8080/realms/master/protocol/openid-connect/token
    type: oauth
  bootstrapServers: kafka-kafka-bootstrap:9092
  consumer:
    config:
      auto.offset.reset: earliest
  http:
    port: 8080
  producer:
    config:
      acks: all
  replicas: 1

• Authentication: The bridge is configured to use OAuth with Keycloak for authentication. It specifies the tokenEndpointUri, clientId, and clientSecret to obtain tokens. Ensure these details are accurate and the Keycloak server is reachable from the Kafka Bridge.
• Bootstrap Servers: kafka-kafka-bootstrap:9092 points to the Kafka bootstrap service. Verify that this address is correct and accessible from within your Kubernetes cluster.
• Producer Configuration: acks: all ensures that the producer waits for all in-sync replicas to acknowledge the message, providing strong durability. However, issues in broker configuration can sometimes cause problems with this setting.
• Consumer Configuration: auto.offset.reset: earliest ensures that the consumer starts reading from the beginning of the topic if no initial offset is found. This is standard but good to confirm.

Kafka Resource Configuration

Here’s the configuration for your Kafka cluster, also managed by the Strimzi operator:

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
metadata:
  name: kafka
  namespace: kafka
spec:
  entityOperator:
    topicOperator: {}
    userOperator: {}
  kafka:
    authorization:
      clientId: kafka
      enableMetrics: false
      superUsers:
      - User:kafka
      tokenEndpointUri: http://keycloak.keycloak.svc.cluster.local:8080/realms/master/protocol/openid-connect/token
      type: keycloak
    config:
      auto.create.topics.enable: true
      default.replication.factor: 3
      min.insync.replicas: 2
      offsets.topic.replication.factor: 3
      transaction.state.log.min.isr: 2
      transaction.state.log.replication.factor: 3
    listeners:
    - authentication:
        clientId: kafka
        clientSecret:
          key: secret
          secretName: broker-oauth-secret
        enableMetrics: false
        jwksEndpointUri: http://keycloak.keycloak.svc.cluster.local:8080/realms/master/protocol/openid-connect/certs
        maxSecondsWithoutReauthentication: 3600
        type: oauth
        userNameClaim: preferred_username
        validIssuerUri: http://keycloak.keycloak.svc.cluster.local:8080/realms/master
      name: plain
      port: 9092
      tls: false
      type: internal
    metadataVersion: 4.1-IV1
    resources:
      limits:
        memory: 4Gi
      requests:
        cpu: 1
        memory: 2Gi
    version: 4.1.0

• Authorization: Kafka uses Keycloak for authorization, with a tokenEndpointUri specified. The superUsers list includes User:kafka, ensuring this user has elevated privileges. Verify that the Keycloak configuration is correct and accessible.
• Kafka Configuration:
  • auto.create.topics.enable: true allows topics to be created automatically. This can be helpful for initial setup but should be managed carefully in production.
  • default.replication.factor: 3 and min.insync.replicas: 2 ensure data is replicated for fault tolerance. The settings for offsets.topic.replication.factor and transaction.state.log should also be set to 3 and 2 respectively to maintain consistency.
• Listeners: An internal listener on port 9092 is configured with OAuth authentication. It's crucial to ensure that the jwksEndpointUri, validIssuerUri, and other OAuth settings are correctly configured and that the Kafka Bridge can authenticate against this listener.

Troubleshooting Steps

Given the configurations and the error message, here are several troubleshooting steps to diagnose and resolve the InitProducerIdResponse error.

1. Verify Keycloak Configuration

• Reachability: Ensure that the Keycloak server is reachable from both the Kafka brokers and the Kafka Bridge. Use kubectl exec to run commands inside the Kafka broker and Kafka Bridge pods to test network connectivity.
• Client Configuration: Double-check the clientId and clientSecret in both the Kafka and Kafka Bridge configurations. Ensure that these credentials are valid and have the necessary permissions in Keycloak.
• Token Endpoint URI: Verify that the tokenEndpointUri is correct and that Keycloak is properly configured to issue tokens for the specified audience and grant type.

2. Check Kafka Broker Logs

Examine the Kafka broker logs for any errors or warnings related to authentication, authorization, or transaction management. These logs can provide valuable insights into why the InitProducerIdResponse is failing.

3. Review Kafka Bridge Permissions in Keycloak

Ensure that the kafka-bridge client has the necessary permissions to produce messages to the specified topics. In Keycloak, check the client's roles and scope mappings to verify that it has the appropriate access.

4. Inspect Network Policies

Kubernetes network policies might be restricting traffic between the Kafka Bridge and the Kafka brokers or Keycloak. Review your network policies to ensure that the Kafka Bridge can communicate with these services.

5. Transactional Settings

Although not explicitly configured, the InitProducerIdResponse error often relates to transactional settings. Ensure that the Kafka cluster is properly configured to support transactions. Key parameters include transaction.state.log.replication.factor and transaction.state.log.min.isr, which should be set to appropriate values (e.g., 3 and 2, respectively) for fault tolerance.

6. Strimzi Operator Logs

Check the Strimzi operator logs for any errors or warnings related to the deployment or configuration of the Kafka cluster or Kafka Bridge. The operator might provide additional information about the cause of the error.

7. Test Kafka Broker Connectivity

Use kafkacat or a similar tool to test the connectivity and authentication to the Kafka brokers directly from within the Kubernetes cluster. This can help isolate whether the issue is with the Kafka Bridge or with the Kafka brokers themselves.

8. Verify Topic Configuration

Ensure that the topic onprem.utv.test-data.add.v1 exists and is correctly configured. Check the topic's replication factor and the number of in-sync replicas to ensure they meet the requirements for message durability.

Reproducing the Issue and Verifying the Fix

The steps to reproduce the issue are well-defined. After applying any fixes, repeat these steps to ensure the problem is resolved:

1. Deploy Kafka and Kafka Bridge: Deploy the Kafka cluster and Kafka Bridge using the Strimzi operator with OAuth enabled and Keycloak authorization.

2. Configure Keycloak: Create kafka and kafka-bridge clients in Keycloak. Configure the necessary resource permissions for the kafka-bridge client, ensuring it has READ, WRITE, CREATE, and DELETE permissions on the relevant topics.

3. Deploy Kafka Bridge: Deploy the Kafka Bridge with the updated configurations.

4. Test Message Production: Use curl to send a message to the Kafka topic via the Kafka Bridge:

   curl -X POST \
     http://localhost:8081/topics/onprem.utv.test-data.add.v1 \
     -H 'content-type: application/vnd.kafka.json.v2+json' \
     -d '{
       "records": [
           {
               "key": "my-key",
               "value": "sales-lead-0001",
               "partition": 0
           }
       ]
   }'
   

   Check the Kafka Bridge logs to ensure the message is successfully produced without the InitProducerIdResponse error.

Conclusion

The Unexpected error in InitProducerIdResponse error in Kafka Bridge can be challenging to diagnose, but by systematically reviewing the configurations, permissions, and network settings, you can identify and resolve the root cause. Focus on verifying the Keycloak integration, Kafka broker settings, and network policies to ensure smooth message production. Remember to leverage the Strimzi operator logs and Kafka broker logs for detailed insights into any underlying issues. By following these steps, you should be able to get your Kafka Bridge producing messages reliably.

For further information on Kafka and Strimzi, refer to the official Apache Kafka Documentation.