Kafka Tutorial: Using Kafka from the command line

May 13, 2017

If you are not sure what Kafka is, start here “What is Kafka?”.

Getting started with Kafka tutorial

Let’s show a simple example using producers and consumers from the Kafka command line.

Download Kafka 0.10.2.x from the Kafka download page. Later versions will likely work, but this was example was done with 0.10.2.x.

We assume that you have Java SDK 1.8.x installed.

We unzipped the Kafka download and put it in ~/kafka-training/, and then renamed the Kafka install folder to kafka. Please do the same.

Next, we are going to run ZooKeeper and then run Kafka Server/Broker. We will use some Kafka command line utilities, to create Kafka topics, send messages via a producer and consume messages from the command line.


Run ZooKeeper for Kafka

Kafka relies on ZooKeeper. To keep things simple, we will use a single ZooKeeper node.

Kafka provides a startup script for ZooKeeper called zookeeper-server-start.sh which is located at ~/kafka-training/kafka/bin/zookeeper-server-start.sh.

The Kafka distribution also provide a ZooKeeper config file which is setup to run single node.

To run ZooKeeper, we create this script in kafka-training and run it.


~/kafka-training/run-zookeeper.sh

#!/usr/bin/env bash
cd ~/kafka-training

kafka/bin/zookeeper-server-start.sh \
   kafka/config/zookeeper.properties


Run run-zookeeper.sh

~/kafka-training
$ ./run-zookeeper.sh


Wait about 30 seconds or so for ZooKeeper to startup.


Run Kafka Server

Kafka also provides a startup script for the Kafka server called kafka-server-start.sh which is located at ~/kafka-training/kafka/bin/kafka-server-start.sh.

The Kafka distribution also provide a Kafka config file which is setup to run Kafka single node, and points to ZooKeeper running on localhost:2181.

To run Kafka, we create this script in kafka-training and run it in another terminal window.


~/kafka-training/run-kafka.sh

#!/usr/bin/env bash
cd ~/kafka-training

kafka/bin/zookeeper-server-start.sh \
   kafka/config/zookeeper.properties


Run run-kafka.sh

~/kafka-training
$ ./run-kafka.sh

Wait about 30 seconds or so for Kafka to startup.

Now let’s create the topic that we will send records on.


Create Kafka Topic

Kafka also provides a utility to work with topics called kafka-topics.sh which is located at ~/kafka-training/kafka/bin/kafka-topics.sh.

We will use this tool to create a topic called my-topic with a replication factor of 1 since we only have one server. We will use thirteen partitions for my-topic, which means we could have up to 13 Kafka consumers.

To run Kafka, create this script in kafka-training\lab1, and run it in another terminal window.


~/kafka-training/lab1/create-topic.sh

#!/usr/bin/env bash

cd ~/kafka-training

# Create a topic
kafka/bin/kafka-topics.sh --create \
  --zookeeper localhost:2181 \
  --replication-factor 1 --partitions 13 \
  --topic my-topic


Run create-topic.sh

~/kafka-training/lab1

$ ./create-topic.sh

Created topic "my-topic".


Notice we created a topic called my-topic.


List Topics

You can see which topics that Kafka is managing using kafka-topics.sh as follows.

Create the file in ~/kafka-training/lab1/list-topics.sh. and run it.


~/kafka-training/lab1/list-topics.sh

#!/usr/bin/env bash

cd ~/kafka-training

# List existing topics
kafka/bin/kafka-topics.sh --list \
    --zookeeper localhost:2181



Notice that we have to specify the location of the ZooKeeper cluster node which is running on localhost port 2181.


Run list-topics.sh

~/kafka-training/lab1
$ ./list-topics.sh
__consumer_offsets
_schemas
my-example-topic
my-example-topic2
my-topic
new-employees


You can see the topic my-topic in the list of topics.


Run Kafka Producer Console

The Kafka distribution provides a command utility to send messages from the command line. It start up a terminal window where everything you type is sent to the Kafka topic.

Kafka provides the utility kafka-console-producer.sh which is located at ~/kafka-training/kafka/bin/kafka-console-producer.sh to send messages to a topic on the command line.

Create the file in ~/kafka-training/lab1/start-producer-console.sh and run it.


~/kafka-training/lab1/start-producer-console.sh

#!/usr/bin/env bash
cd ~/kafka-training

kafka/bin/kafka-console-producer.sh \
    --broker-list localhost:9092 \
    --topic my-topic


Notice that we specify the Kafka node which is running at localhost:9092.


Run start-producer-console.sh and send at least four messages

~/kafka-training/lab1
$ ./start-producer-console.sh
This is message 1
This is message 2
This is message 3
Message 4
Message 5


In order to see these messages, we will need to run the consumer console.


Run Kafka Consumer Console

The Kafka distribution provides a command utility to see messages from the command line. It displays the messages in various modes.

Kafka provides the utility kafka-console-consumer.sh which is located at ~/kafka-training/kafka/bin/kafka-console-producer.sh to receive messages from a topic on the command line.

Create the file in ~/kafka-training/lab1/start-consumer-console.sh and run it.


~/kafka-training/lab1/start-producer-console.sh

#!/usr/bin/env bash
cd ~/kafka-training

kafka/bin/kafka-console-consumer.sh \
    --bootstrap-server localhost:9092 \
    --topic my-topic \
    --from-beginning


Notice that we specify the Kafka node which is running at localhost:9092 like we did before, but we also specify to read all of the messages from my-topic from the beginning --from-beginning.


Run start-consumer-console.sh in another terminal

~/kafka-training/lab1
$ ./start-consumer-console.sh
Message 4
This is message 2
This is message 1
This is message 3
Message 5
Message 6
Message 7


Notice that the messages are not coming in order. This is because we only have one consumer so it is reading the messages from all 13 partitions. Order is only guaranteed within a partition.


Review of using Kafka from the command line

What server do you run first?

You need to run ZooKeeper than Kafka.

What tool do you use to create a topic?

kafka-topics.sh

What tool do you use to see topics?

kafka-topics.sh

What tool did we use to send messages on the command line?

kafka-console-producer.sh

What tool did we use to view messages in a topic?

kafka-console-consumer.sh

Why were the messages coming out of order?

The messages were being sharded among 13 partitions.

How could we get the messages to come in order from the consumer?

We could use only one partition or start up 13 consumers.


More about Kafka

To learn about Kafka see Kafka architecture, Kafka topic architecture and Kafka producer architecture.



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