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50 mostly-asked Apache Kafka interview questions

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Core Kafka Fundamentals

  1. What is Apache Kafka?
  2. Why do companies use Apache Kafka?
  3. What are Kafka topics?
  4. Explain partitions in Kafka.
  5. What is an offset in Kafka?
  6. What is a broker?
  7. What are producers and consumers?
  8. What is a consumer group?
  9. How does Kafka achieve fault tolerance?
  10. What is replication factor?

Architecture & Design

  1. How does Kafka store data?
  2. Explain the role of ZooKeeper (or KRaft mode).
  3. What are leader and follower replicas?
  4. What is ISR (In-Sync Replica)?
  5. How does Kafka guarantee order?

Performance & Tuning

  1. What are key Kafka configs for performance tuning?
  2. How do you optimize Kafka throughput?
  3. When should you increase partitions?
  4. Explain batching and compression.
  5. What metrics would you monitor in a Kafka cluster?

Delivery Semantics

  1. What are delivery guarantees in Kafka (at-most-once, at-least-once, exactly-once)?
  2. How do idempotent producers work?
  3. What is Kafka Transaction API?
  4. How do you handle consumer lag?
  5. How do you handle poison-pill messages?

Kafka Ecosystem

  1. What is Kafka Connect?
  2. What is Schema Registry and why use it?
  3. What is Kafka Streams?
  4. What is ksqlDB?
  5. How do connectors differ from streams?

Commands & CLI

  1. How to list topics via CLI?
  2. How to add/remove configs on a topic?
  3. How to consume messages from the beginning?
  4. How to view broker cluster details? (Controller, brokers)
  5. How to alter partition count using CLI?

Real-World & Scenario Questions

  1. What happens if consumers are slower than producers?
  2. How would you design a real-time analytics pipeline using Kafka?
  3. How do you do load balancing across consumers?
  4. How would you handle Kafka broker failure?
  5. How do you handle large messages in Kafka?

Advanced & Experienced Topics

  1. What are leader epochs?
  2. How do you ensure schema evolution compatibility?
  3. How would you secure a Kafka cluster?
  4. How to back up and restore Kafka data?
  5. How do Kafka interceptors work?

Java / Developer Specific

  1. How to integrate Kafka with Spring Boot?
  2. How do you serialize/deserialize custom objects?
  3. What are Kafka AdminClient APIs?
  4. How do you write a Kafka producer/consumer in Java?
  5. How to handle retries and errors in Kafka clients?

Tips for Kafka interviews:

  • Be ready to explain real-world use cases (data pipelines, event sourcing).
  • Expect scenario-based questions on scalability and failure handling.
  • Know key configs and metrics — MNCs often probe practical knowledge beyond theoretic definitions.