How to Set Replication Factor in Kafka: Simple Guide

To set the replication.factor in Kafka, specify it when creating a topic using the --replication-factor option with the kafka-topics.sh command. This controls how many copies of each partition Kafka keeps across brokers for fault tolerance.

Syntax

The replication factor is set during topic creation using the Kafka command line tool. The key parts are:

• --create: to create a new topic
• --topic: the name of the topic
• --partitions: number of partitions
• --replication-factor: number of copies of each partition
• --bootstrap-server: Kafka broker address

bash

kafka-topics.sh --create --topic <topic-name> --partitions <num> --replication-factor <num> --bootstrap-server <broker-address>

Example

This example creates a topic named my-topic with 3 partitions and a replication factor of 2, meaning each partition has 2 copies on different brokers.

bash

kafka-topics.sh --create --topic my-topic --partitions 3 --replication-factor 2 --bootstrap-server localhost:9092

Output

Created topic "my-topic".

Common Pitfalls

Common mistakes when setting replication factor include:

• Setting replication factor higher than the number of brokers available, which causes topic creation to fail.
• Trying to change replication factor after topic creation without using proper reassignment tools.
• Not specifying --replication-factor during creation, which defaults to 1 and risks data loss if a broker fails.

bash

## Wrong: replication factor higher than brokers
kafka-topics.sh --create --topic test-topic --partitions 1 --replication-factor 5 --bootstrap-server localhost:9092

## Right: replication factor less or equal to brokers
kafka-topics.sh --create --topic test-topic --partitions 1 --replication-factor 1 --bootstrap-server localhost:9092

Output

Error: replication factor: 5 larger than available brokers: 3
Created topic "test-topic".

Quick Reference

Option	Description
--create	Create a new Kafka topic
--topic	Name of the topic
--partitions	Number of partitions for the topic
--replication-factor	Number of copies of each partition
--bootstrap-server	Kafka broker address

Key Takeaways

Set replication factor during topic creation with --replication-factor option.

Replication factor must not exceed the number of Kafka brokers.

Replication factor controls data durability by keeping copies on multiple brokers.

Changing replication factor after creation requires partition reassignment tools.

Default replication factor is 1 if not specified, which risks data loss.