65 Apache Kafka interview questions to hire top talent (+ 25 sample answers)

Assessing technical skills accurately and objectively is more important than ever, especially when hiring data engineers and software developers to work on your big data projects. 

And, if your team uses Apache Kafka, you need to make sure future hires are proficient with it and know how to use it to handle massive streams of data. 

But how can you do that?

The easiest way to identify the best person to hire is to:

• Use pre-employment skills testing to filter out those who simply don’t have the right skills

• Interview shortlisted candidates to zero in on your top talent

For the first step, you can use our Data Analytics in AWS, Apache Spark, or Fundamentals of Statistics and Probability tests; for more ideas, check our extensive test library.

To help you with the second step, we’ve selected 65 Apache Kafka interview questions you can ask applicants during interviews. You’ll also find sample answers to 25 of them, so even if you’re no Kafka expert yourself, you’ll be able to spot the best talent.

Top 25 Kafka interview questions to hire the best data engineers and software developers

Below, you’ll find our selection of the best 25 interview questions you can use during interviews to evaluate candidates’ technical knowledge and hands-on experience with Apache Kafka. 

We’ve also included sample answers to help you assess responses, even if you’re not a Kafka expert yourself. 

1. Can you describe the basic architecture of Kafka?

Kafka is a distributed stream-processing platform, which has a storage layer and a compute layer. The key components of its architecture are:

• Producers

• Consumers

• Brokers

• Streams

• A Connector API

• The ZooKeeper

Look for descriptions of how Kafka enables real-time data feeding and stream processing.

2. What are producers and consumers in Kafka?

Producers are entities that publish data to Kafka topics; consumers are entities that subscribe to topics and process the data. 

Skilled candidates might also talk about consumer groups and the role of offset management in ensuring the correct consumption of data.

3. What is a Kafka broker?

A broker is a server in the Kafka cluster that stores data and serves client requests. 

Brokers handle data replication, request processing, and contribute to the overall fault tolerance of the system.

4. What is a topic in Kafka?

A topic is a category or feed name to which records are published. They’re partitionable and log-based, enabling the distribution and parallel processing of data across multiple brokers.

5. What is a partition in a Kafka topic?

Partitions are subsections of a topic where data is stored. Partitions enable Kafka to scale horizontally and support multiple consumers by dividing the data across different brokers. 

Mentioning the role of partitions in fault tolerance through replication is a plus.

6. How does Kafka ensure message durability?

The replication of partitions across multiple brokers ensures message durability; replication also uses write-ahead logs. Developers can configure retention policies in Kafka, which means they can store data even after it’s consumed.

7. How do you install Kafka on a server?

Do install Kafka on a server, an engineer would need to: 

• Download Kafka

• Configure ZooKeeper, or another coordination service if using a newer version

• Set up the Kafka configuration files

• Start the Kafka server

Knowledge of system requirements and basic troubleshooting is a plus.

8. How would you secure a Kafka cluster?

Top candidates would use multiple layers of security and strategies such as:

• SSL/TLS for encryption of data in transit

• SASL/SCRAM for authentication

• A Kerberos integration

• Network policies for controlling access to the Kafka cluster 

• ACLs (Access Control Lists) for authorizing actions by users or groups on specific topics

9. What is the role of the server.properties file?

The server.properties file is the primary configuration file for a Kafka broker. It includes settings related to the broker, network, logs, replication, and other operational parameters. 

Look for candidates to mention specific configurable properties that are crucial for setting up and managing Kafka brokers, such as broker.id, log.dirs, and zookeeper.connect.

10. How do you monitor the health of a Kafka cluster?

Here are some of the ways to monitor the health of clusters:

• Checking broker states

• Verifying consumer group status

• Assessing replication factors

• Checking logs for errors

• using JMX (Java Management Extensions) to monitor performance metrics

Top applicants will know how to use the Kafka command-line tools such as kafka-topics.sh to view topic details and kafka-consumer-groups.sh to get consumer group information.

11. What tools can you use for Kafka monitoring?

Skilled candidates will mention several tools, including:

• Kafka's own JMX metrics for in-depth monitoring at the JVM level

• Prometheus with Grafana for visualizing metrics

• Elastic Stack (Elasticsearch, Logstash, Kibana) for log aggregation and analysis

• Datadog, New Relic, or Dynatrace for integrated cloud monitoring

Use our Elasticsearch test to evaluate candidates’ proficiency with this tool. 

12. How would you upgrade a Kafka cluster with minimal downtime?

This question enables you to assess candidates’ hands-on experience with Kafka. Look for smart strategies such as performing a rolling upgrade, which involves updating brokers one at a time to avoid downtime. 

Candidates should mention the importance of backing up configurations and data, testing the new version in a staging environment first, and carefully monitoring the cluster during the upgrade process. A strong understanding of version compatibility and configuration changes between Kafka versions is key.

13. Explain the concept of Kafka MirrorMaker.

Kafka MirrorMaker is a tool used for cross-cluster data replication. It enables data mirroring between two Kafka clusters, which is particularly useful for disaster recovery and geo-replication scenarios. 

MirrorMaker works by using consumer and producer configurations to pull data from a source cluster and push it to a destination cluster.

14. What is exactly-once processing in Kafka?

Exactly-once processing ensures that records don’t get lost and aren’t seen more than once, despite failures. This is critical in applications where duplicate processing can lead to significant issues. 

Candidates might discuss Kafka’s transactional APIs, which use idempotent producers and transactional consumers for exactly-once processing.

15. How does partitioning work in Kafka?

Partitioning involves the division of topics into multiple segments across brokers, in order to: 

• Enable parallel processing

• Increase throughput

• Enhance fault tolerance

Strong candidates will explain how Kafka assigns partitions to consumers in a group and how partitions ensure load balancing within a cluster.

16. What are ISR in Kafka?

ISR (short for In-Sync Replicas) are replicas of a Kafka partition that are fully in sync with the leader. They’re critical for ensuring data durability and consistency. If a leader fails, one of the ISRs can become the new leader. 

17. How do you reassign partitions in Kafka?

Reassigning partitions to different brokers requires using command-line tools like kafka-reassign-partitions.sh to generate a reassignment JSON file and then execute the reassignment. 

Developers also need to balance the load across brokers and minimize the impact on the cluster performance during this process.

18. What might cause latency issues in Kafka?

There are several potential causes of latency, such as:

• High volume of network traffic or inadequate network hardware

• Disk I/O bottlenecks due to high throughput or slow disks

• Large batch sizes or infrequent commits causing delays

• Inefficient consumer configurations or slow processing of messages

Look for candidates who can explain how they’d diagnose and mitigate these issues, such as adjusting configurations and upgrading hardware.

19. How can you reduce disk usage in Kafka?

Some of the best ways to reduce disk usage are to: 

• Adjust log retention settings to keep messages for a shorter duration

• Use log compaction to only retain the last message for each key

• Configure message cleanup policies effectively

• Compress messages before sending them to Kafka

20. What are some best practices for scaling a Kafka deployment?

To scale a deployment successfully, developers should:

• Size and partition topics to distribute load evenly across the cluster

• Use adequate hardware to support the intended load

• Monitor performance and adjust configurations as necessary

• Use replication to improve availability and fault tolerance

• Use Kafka Streams or Kafka Connect for integrating and processing data at scale

21. What are the implications of increasing the number of partitions in a Kafka topic?

Increasing partitions can improve concurrency and throughput but also has its downsides, because it might: 

• Increase overhead on the cluster due to more open file handles and additional replication traffic

• Lead to possible imbalance in data distribution 

• Lead to longer rebalancing times and 

• Make it more difficult to manage consumer groups

Careful planning and testing before altering partitions is key. 

22. What are some security risks when working with Kafka?

Some of Kafka’s security risks are:

• Unauthorized data access

• Data tampering

• Service disruption

It’s essential to secure network access to Kafka, protect data at rest and in transit, and put in place robust authentication and authorization procedures. 

23. How does Kafka support GDPR compliance?

Kafka ensures robust data protection thanks to its: 

• Data encryption features, both in transit using SSL/TLS and at rest

• Ability to handle data retention policies 

• Deletion capabilities that can be used to comply with GDPR’s right to erasure

• Logging and auditing features to track data access and modifications

Need to evaluate candidates’ GDPR knowledge and their ability to handle sensitive data?

Use our GDPR and Privacy test.

24. What authentication mechanisms can you use in Kafka?

Kafka supports:

• SSL/TLS for encrypting data and optionally authenticating clients using certificates

• SASL (Simple Authentication and Security Layer) which supports mechanisms like GSSAPI (Kerberos), PLAIN, and SCRAM to secure Kafka brokers against unauthorized access

• Integration with enterprise authentication systems like LDAP

25. How can you use Kafka’s quota feature to control client traffic?

Kafka quotas can be set to limit the byte-rate for producing and consuming messages, which prevents the overloading of Kafka brokers by aggressive clients. 

Candidates might discuss setting quotas at the broker level to manage bandwidth and storage and explain how this can help maintain the Kafka cluster’s stability.

26. Describe an instance where Kafka might lose data and how you would prevent it.

A good response will mention cases such as unclean leader elections, broker failures, or configuration errors that lead to data loss. 

Candidates should explain how they’d configure Kafka’s replication factors, min.insync.replicas, and acknowledgment settings to prevent data loss. They should also mention they’d do regular backups and set up consistent monitoring to prevent issues. 

40 more Kafka interview questions you can ask candidates

Looking for more questions you can ask candidates to evaluate their proficiency in Apache Kafka? 

Below, you can find 40 more questions you can use during interviews, ranging from easy (at the top), to more challenging (towards the bottom of the list). 

1. How do you use Kafka with Spark?

2. What are some common mistakes developers make with Kafka?

3. What are some alternatives to Kafka?

4. Explain the role of ZooKeeper in Kafka.

5. What is a Consumer Group in Kafka?

6. What are offsets in Kafka?

7. How do you configure a Kafka producer?

8. How do you configure a Kafka consumer?

9. How does Kafka Connect work?

10. How would you handle Kafka’s logs?

11. How does Kafka handle failover?

12. What is log compaction in Kafka?

13. How can you optimize Kafka throughput?

14. How do you handle large messages in Kafka?

15. How do you troubleshoot network issues in Kafka?

16. How would you handle an instance where consumers are slower than producers?

17. What steps would you take if your Kafka cluster unexpectedly goes down?

18. How would you retrieve old messages in Kafka?

19. How do you ensure message order in a Kafka topic?

20. How do you manage offsets for a consumer in Kafka?

21. How do you produce and consume messages to Kafka using the Java API?

22. What are some other languages that Kafka supports?

23. How do you use Kafka with Hadoop?

24. Explain how transactions are handled in Kafka.

25. How do you implement idempotence in Kafka?

26. What is the role of timestamps in Kafka messages?

27. How do you encrypt data in Kafka?

28. How do you audit data access in Kafka?

29. What is SASL/SCRAM in Kafka?

30. Explain how to configure TLS for Kafka.

31. How do you protect sensitive data in Kafka?

32. What are the best practices for Kafka data modeling?

33. How do you handle data retention in Kafka?

34. What are the limitations of Kafka Streams?

35. How does Kafka fit into a microservices architecture?

36. Explain the role of Kafka in a cloud environment.

37. How do you back up Kafka data?

38. What is a dead letter queue in Kafka?

39. How do you use Kafka for event sourcing?

40. Can you use Kafka for batch processing?

If you need more ideas, check out our Spark interview questions and our data engineer interview questions.

Use the right skills assessments to hire top Kafka talent

Assessing applicants’ Kafka skills quickly and reliably is essential for making the right hire. For this, you need to be equipped with the right skills tests and interview questions. 

This way, you’re not leaving anything to chance and can be sure that the person you hire will have what it takes to contribute to your big data projects. 

To chat with one of our experts and find out whether TestGorilla is the right platform for you, simply sign up for a free demo. Or, if you prefer to test our tests yourself (pun intended), check out our free forever plan.