Apache Kafka Cheat Sheet 2026

The 30 highest-yield Apache Kafka facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Which CLI tool is used to manage Kafka ACLs? → kafka-acls.sh
2. What HTTP endpoint checks the status of a running connector in Kafka Connect's REST API? → GET /connectors/{name}/status
3. What is the purpose of the `__consumer_offsets` internal topic in Kafka? → Stores committed consumer group offsets so consumers can resume after restart
4. What Kafka configuration property specifies the security protocol for a listener? → listener.security.protocol.map
5. What is a KStream in Kafka Streams? → An unbounded sequence of individual key-value records (changelog stream)
6. What does the `log.dirs` broker configuration specify? → One or more comma-separated directories where Kafka stores partition log data on disk
7. In Kafka, what is referred to as a broker? → Server
8. What is the significance of a Kafka Producer API? → It is responsible for covering two producers
9. What is the primary role of the Kafka Controller broker in a cluster? → It handles partition leader election and broker failure recovery
10. What is the Kafka Streams DSL `groupByKey()` method used for? → Groups records by their existing key as a prerequisite for aggregation operations
11. What is the function of the Kafka `__transaction_state` internal topic? → Stores the state of ongoing and completed transactions managed by transaction coordinators
12. Which setting must be enabled for a Kafka consumer to commit offsets automatically? → enable.auto.commit=true
13. How do you deploy a connector in Kafka Connect distributed mode? → By posting a JSON configuration to the Connect REST API
14. What does the `kafka-dump-log.sh` tool do? → Prints the raw contents of Kafka log segment files for low-level debugging
15. What is the effect of setting `retries=0` on a Kafka producer? → The producer will not retry failed sends, potentially losing messages on transient errors
16. Which Kafka configuration enables SSL mutual authentication (mTLS)? → ssl.client.auth=required on the broker side
17. Which Kafka tool applies dynamic broker configuration changes without a restart? → kafka-configs.sh --alter --entity-type brokers
18. Which JMX metric reports the number of under-replicated partitions in a Kafka cluster? → kafka.server:type=ReplicaManager,name=UnderReplicatedPartitions
19. Where is the `server.properties` file used in a Kafka deployment? → It is the main broker configuration file containing all broker settings
20. Apache Kafka is used to run a cluster of one or more servers known as ____. → Brokers
21. Which CLI tool is used to list, describe, and reset consumer group offsets in Kafka? → kafka-consumer-groups.sh
22. An application can publish streams of records using Apache Kafka's ______ Api. → Producer
23. What is the role of `buffer.memory` in a Kafka producer? → Total bytes of memory the producer uses to buffer records waiting to be sent
24. Which consumer configuration determines how frequently the consumer offsets are committed automatically? → auto.commit.interval.ms
25. What is the purpose of the `max.poll.records` consumer configuration? → Limits the maximum number of records returned in a single poll() call
26. What does the `fetch.min.bytes` consumer configuration control? → Minimum data the broker returns in a fetch response before sending
27. What does Active Controller Count equal in a healthy Kafka cluster? → Exactly 1, since only one broker can be the controller at a time
28. Which method is used to materialize a KTable into a queryable local state store? → Materialized.as()
29. What is the purpose of the `kafka-reassign-partitions.sh` tool? → To move partition replicas to different brokers
30. What does the `filter()` operation do in a Kafka Streams topology? → Passes only records that satisfy a given predicate, dropping the rest