Logstash Error: Kafka Leader not available - Common Causes & Fixes

Brief Explanation

The "Kafka Leader not available" error in Logstash occurs when the Logstash Kafka input or output plugin cannot connect to the leader broker for a particular Kafka topic partition. This error indicates that Logstash is unable to read from or write to the Kafka cluster due to leadership issues.

Common Causes

1. Kafka broker(s) are down or unreachable
2. Network connectivity issues between Logstash and Kafka cluster
3. Misconfiguration of Kafka broker addresses in Logstash
4. Kafka cluster undergoing leadership election or rebalancing
5. Insufficient replicas for the affected topic partitions

Troubleshooting and Resolution Steps

1. Verify Kafka cluster health:

   • Check if all Kafka brokers are running
   • Ensure there are no network issues between Logstash and Kafka

2. Review Logstash configuration:

   • Confirm that the Kafka broker addresses are correct
   • Verify that the topic and partition configurations are accurate

3. Check Kafka topic status:

   • Use Kafka command-line tools to check topic and partition status
   • Ensure that the topic has the correct number of replicas and in-sync replicas

4. Increase connection timeout and retry settings:

   • Adjust retry_backoff_ms and reconnect_backoff_ms in Logstash Kafka plugin configuration

5. Monitor Kafka logs for any leadership changes or errors

6. If the issue persists, consider restarting Kafka brokers or re-creating the affected topics

Best Practices

• Implement proper monitoring for both Logstash and Kafka clusters
• Use multiple Kafka brokers for high availability
• Configure appropriate replication factor for Kafka topics
• Regularly update Logstash and Kafka to the latest stable versions
• Implement circuit breakers or error handling in Logstash pipelines to manage Kafka connectivity issues

Frequently Asked Questions

Q: How long should I wait before considering the "Leader not available" error as persistent?
A: It's recommended to wait for at least 5-10 minutes, as temporary leadership changes or cluster rebalancing can cause short-lived errors. If the error persists beyond this time, further investigation is needed.

Q: Can this error occur even if all Kafka brokers are running?
A: Yes, it can occur if there are network issues, misconfiguration, or if the Kafka cluster is undergoing internal changes like leadership election.

Q: Will increasing the number of Kafka brokers help prevent this error?
A: While increasing the number of brokers can improve availability, it doesn't guarantee prevention of this error. Proper configuration and monitoring are equally important.

Q: How can I prevent data loss during such errors?
A: Implement proper error handling in Logstash, use persistent queues, and ensure your Kafka topics have an appropriate replication factor. Also, consider implementing a dead-letter queue for messages that fail to be processed.

Q: Is this error specific to certain versions of Logstash or Kafka?
A: This error can occur in various versions of Logstash and Kafka. However, staying updated with the latest stable versions can help mitigate known issues related to leadership and connectivity.