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 Kafka Streams DSL `groupByKey()` method used for? → Groups records by their existing key as a prerequisite for aggregation operations
10. What is the function of the Kafka `__transaction_state` internal topic? → Stores the state of ongoing and completed transactions managed by transaction coordinators
11. Which setting must be enabled for a Kafka consumer to commit offsets automatically? → enable.auto.commit=true
12. How do you deploy a connector in Kafka Connect distributed mode? → By posting a JSON configuration to the Connect REST API
13. 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
14. Which Kafka configuration enables SSL mutual authentication (mTLS)? → ssl.client.auth=required on the broker side
15. Which Kafka tool applies dynamic broker configuration changes without a restart? → kafka-configs.sh --alter --entity-type brokers
16. Where is the `server.properties` file used in a Kafka deployment? → It is the main broker configuration file containing all broker settings
17. Apache Kafka is used to run a cluster of one or more servers known as ____. → Brokers
18. An application can publish streams of records using Apache Kafka's ______ Api. → Producer
19. 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
20. Which consumer configuration determines how frequently the consumer offsets are committed automatically? → auto.commit.interval.ms
21. What is the purpose of the `max.poll.records` consumer configuration? → Limits the maximum number of records returned in a single poll() call
22. What does the `fetch.min.bytes` consumer configuration control? → Minimum data the broker returns in a fetch response before sending
23. Which method is used to materialize a KTable into a queryable local state store? → Materialized.as()
24. What does the `filter()` operation do in a Kafka Streams topology? → Passes only records that satisfy a given predicate, dropping the rest
25. What determines which partition a keyed message is written to? → hash(key) % number_of_partitions
26. How does a follower replica know it is out of sync with the leader? → When its LEO lags behind the leader's LEO for more than replica.lag.time.max.ms
27. When using `assign()` instead of `subscribe()`, what is the consumer responsible for? → Manually managing partition assignment without group coordinator involvement
28. What is a KTable in Kafka Streams? → A changelog stream interpreted as a table where each record is an upsert by key
29. What is the largest message a Kafka server can receive? → 1,000,000 bytes
30. Consumers utilize Apache Kafka's control records to → filter out aborted transactional messages