Apache Kafka 4 Cheatsheet

Start a broker (KRaft)

• Generate a cluster ID — Create a random ID for a new cluster.
• Format the log directories — Prepare storage for a single-node cluster. Do this once per new cluster.
• Start the broker — Start Kafka with the default configuration.
• Check the broker is reachable — List the APIs and versions the broker supports.
• Check the controller quorum — Show the KRaft quorum status and who the leader is.

Topics

• Create a topic — Create a topic with three partitions.
• List topics — Show the topics in the cluster.
• Describe a topic — Show partitions, leaders and replicas.
• Add partitions — Increase a topic's partition count. You can't reduce it.
• Delete a topic — Delete a topic and its data.
• Set a topic's retention — Keep messages for 7 days.
• See the latest offsets — Print the end offset of each partition.

Producing and consuming

• Send messages from the terminal — Type one message per line. Press Ctrl+C to stop.
• Send keyed messages — Type key:value pairs. Messages with the same key go to the same partition.
• Read messages from the start — Read a topic from the earliest offset.
• Show keys and timestamps — Print each message's key and timestamp too.
• Consume as part of a group — Join a consumer group so the group's offsets are saved.

Consumer groups

• List consumer groups — Show all consumer groups in the cluster.
• Check consumer lag — Show each partition's current offset, end offset and lag for a group.
• Preview an offset reset — Show what resetting to the earliest offset would do, without changing anything. The group must have no active consumers.
• Reset offsets — Move the group back to the earliest offset so it reprocesses messages.
• Delete a consumer group — Delete a group that has no active members.

Performance and debugging

• Test producer throughput — Send 100,000 records of 100 bytes as fast as possible.
• Test consumer throughput — Read 100,000 messages and report the rate.
• Inspect a log segment — Print the messages in a log segment file on a broker's disk.

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