Demo: Using kafka-leader-election.sh

The demo shows how to use kafka-leader-election.sh command-line utility for Partition Leader Election.

The demo is made up of the following steps:

Start Kafka Cluster
Create Topic
Shutting Down Leader Broker
Trigger Preferred Leader Election

Start Kafka Cluster

You’ll be using kafka-docker project to run Apache Kafka in Docker (using Docker Compose).

docker-compose up -d --scale=kafka=3

The goal is to run 3 brokers as easily as possible (let me know if you know a simpler way. Thanks!).

Create Topic

In this step you’ll create a topic with 3 partitions (one for every broker in the cluster) and 2 replicas.

docker exec -it kafka-docker_kafka_1 /bin/bash

kafka-topics.sh \
    --bootstrap-server :9092 \
    --create \
    --topic demo-kafka-leader-election \
    --partitions 3 \
    --replication-factor 2

Review the leader and ISR brokers. Yours may be different.

$ kafka-topics.sh \
    --bootstrap-server :9092 \
    --describe \
    --topic demo-kafka-leader-election
Topic: demo-kafka-leader-election	PartitionCount: 3	ReplicationFactor: 2	Configs: segment.bytes=1073741824
	Topic: demo-kafka-leader-election	Partition: 0	Leader: 1002	Replicas: 1002,1001	Isr: 1002,1001
	Topic: demo-kafka-leader-election	Partition: 1	Leader: 1001	Replicas: 1001,1003	Isr: 1001,1003
	Topic: demo-kafka-leader-election	Partition: 2	Leader: 1003	Replicas: 1003,1002	Isr: 1003,1002

Shutting Down Leader Broker

In this step, you’re going to shut down a leader broker to simulate a broker failure. That triggers a leader election and promote the other broker (in the ISR list) to become the leader.

docker stop kafka-docker_kafka_2

You should have 2 brokers up and running.

$ docker ps
CONTAINER ID        IMAGE                    COMMAND                  CREATED             STATUS              PORTS                                                NAMES
f7224b2bdf90        kafka-docker_kafka       "start-kafka.sh"         2 minutes ago       Up 2 minutes        0.0.0.0:32785->9092/tcp                              kafka-docker_kafka_3
52ac4b64648e        wurstmeister/zookeeper   "/bin/sh -c '/usr/sb…"   2 minutes ago       Up 2 minutes        22/tcp, 2888/tcp, 3888/tcp, 0.0.0.0:2181->2181/tcp   kafka-docker_zookeeper_1
ad05db816dc1        kafka-docker_kafka       "start-kafka.sh"         2 minutes ago       Up 2 minutes        0.0.0.0:32784->9092/tcp                              kafka-docker_kafka_1

Review the leaders.

$ kafka-topics.sh \
    --bootstrap-server :9092 \
    --describe \
    --topic demo-kafka-leader-election
Topic: demo-kafka-leader-election	PartitionCount: 3	ReplicationFactor: 2	Configs: segment.bytes=1073741824
	Topic: demo-kafka-leader-election	Partition: 0	Leader: 1001	Replicas: 1002,1001	Isr: 1001
	Topic: demo-kafka-leader-election	Partition: 1	Leader: 1001	Replicas: 1001,1003	Isr: 1001,1003
	Topic: demo-kafka-leader-election	Partition: 2	Leader: 1003	Replicas: 1003,1002	Isr: 1003

Trigger Preferred Leader Election

In this step, you will trigger preferred leader election for the partitions with the other leader elected (non-preferred leader).

Let’s bring the stopped broker up.

$ docker start kafka-docker_kafka_2
kafka-docker_kafka_2

Review the leaders.

$ kafka-topics.sh \
    --bootstrap-server :9092 \
    --describe \
    --topic demo-kafka-leader-election
Topic: demo-kafka-leader-election	PartitionCount: 3	ReplicationFactor: 2	Configs: segment.bytes=1073741824
	Topic: demo-kafka-leader-election	Partition: 0	Leader: 1001	Replicas: 1002,1001	Isr: 1001,1002
	Topic: demo-kafka-leader-election	Partition: 1	Leader: 1001	Replicas: 1001,1003	Isr: 1001,1003
	Topic: demo-kafka-leader-election	Partition: 2	Leader: 1003	Replicas: 1003,1002	Isr: 1003,1002

Time to fix the partition 0 so the broker 1002 is the leader again.

kafka-leader-election.sh \
  --bootstrap-server :9092 \
  --topic demo-kafka-leader-election \
  --partition 0 \
  --election-type preferred

You should see the following message for a successful election.

Successfully completed leader election (PREFERRED) for partitions demo-kafka-leader-election-0

Review the leaders.

$ kafka-topics.sh \
    --bootstrap-server :9092 \
    --describe \
    --topic demo-kafka-leader-election
Topic: demo-kafka-leader-election	PartitionCount: 3	ReplicationFactor: 2	Configs: segment.bytes=1073741824
	Topic: demo-kafka-leader-election	Partition: 0	Leader: 1002	Replicas: 1002,1001	Isr: 1001,1002
	Topic: demo-kafka-leader-election	Partition: 1	Leader: 1001	Replicas: 1001,1003	Isr: 1001,1003
	Topic: demo-kafka-leader-election	Partition: 2	Leader: 1003	Replicas: 1003,1002	Isr: 1003,1002

Demo: Using kafka-leader-election.sh