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Running Kafka in Docker

Introduction

Running Apache Kafka with Docker can be harder than it should be. Or perhaps it’s easy once you know what exactly you need to do. In this post, I’m going to discuss about how I run Kafka in Docker.


Table of Contents


What is Kafka?

Apache Kafka is a distributed real-time event streaming and ingestion platform that is capable of handling very large volume of data. With the rise in the Microservices architecture in recent years, Kafka has gained a lot of popularity.

Is this going to be a production or a development setup?

Contrary to the popular belief that Docker is an amazing tool only meant for production deployments, Docker can be pretty useful for development environments also. While the steps listed here are applicable for a production environment as well, there are many more things one needs to take into consideration for a production setup. This article is more geared towards creating a development setup than a production one.

Why Bitnami images over Confluent?

Unlike many other software, Apache Kafka does not have an official Docker image. Apache Kafka as an open source project only releases compiled tarball packages that can be extracted and executed on Linux, MacOS or Windows. There are other third-party companies including Confluent and Bitnami that package and release Kafka Docker images. Although Confluent images are more popular as they are from a company that provides commercial support for Kafka deployments, the reason I chose Bitnami over Confluent is that their images seemed simpler to start with for a development environment, were up to date with upstream and had good documentation.

Setting up a Docker network

In a Kafka environment, usually there will be multiple components interacting with each other. I will be creating a dedicated Docker network that will be used by the containers to connect with each other. The following command creates a Docker network named kafka-net.

docker network create kafka-net

Starting Zookeeper

Zookeeper is another software from Apache that is used by Kafka to store metadata information. We will need to start a Zookeeper instance before spawning the Kafka broker containers.

docker run -d --rm --network kafka-net \
                    -p 2181:2181 \
                    --name zookeeper \
                    -e ALLOW_ANONYMOUS_LOGIN=yes \
                    bitnami/zookeeper:latest

A few points about the above command:

Starting one Kafka broker

The next step is to start a Kafka broker instance with the following command.

docker run -d --rm --network kafka-net \
            -p 9092:9092 \
            -p 29092:29092 \
            --name kafka \
            -e ALLOW_PLAINTEXT_LISTENER=yes \
            -e KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181 \
            -e KAFKA_CFG_LISTENER_SECURITY_PROTOCOL_MAP=INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT \
            -e KAFKA_CFG_LISTENERS=INTERNAL://:9092,EXTERNAL://:29092 \
            -e KAFKA_CFG_ADVERTISED_LISTENERS=INTERNAL://kafka:9092,EXTERNAL://localhost:29092 \
            -e KAFKA_CFG_INTER_BROKER_LISTENER_NAME=INTERNAL \
            bitnami/kafka:2.5.0

A few points to note about the above command:

Testing the cluster

Now that we have our local Kafka cluster up and running, it’s time for testing it out. For this we will need a Kafka producer that will publish data to our Kafka cluster and a consumer that will listen to it. While we can use the kafka-console-producer.sh and the kafka-console-consumer.sh scripts that ship with Kafka, I will use a utility called kafkacat. Although kafkacat can be installed in multiple ways, it can also be used as a Docker container without the need to install it. This is the method that I am going to use here.

Connect from within the kafka-net

The producer

The following command creates a kafkacat Docker container that reads input from the stdin and publishes to the test-topic. Topics will be automatically created on use.

docker run -it --network kafka-net edenhill/kafkacat:1.5.0 \
				-b kafka:9092 \
				-t test-topic \
				-P

Noticed the --network kafka-net flag? It tells Docker to attach our kafkacat container to the kafka-net network that we created earlier. And probably you have already guessed that we are going to use the INTERNAL listener here. This is the reason why we are passing kafka:9092 as the broker address.

The consumer

In a separate terminal, use the following command to create a kafkacat Docker container that reads from the test-topic and prints to the stdout.

docker run -it --network kafka-net edenhill/kafkacat:1.5.0 \
				-b kafka:9092 \
				-t test-topic \
				-C

Now when you type something in the producer terminal and press enter, you should see the same text being printed by our consumer on the consumer terminal.

kafka-on-docker-internal-clients

Press Ctrl + D to end the producer session.

Connect from outside of kafka-net

Now if we want to do the same thing using the EXTERNAL listener, here are the commands:

# producer
docker run -it --network host edenhill/kafkacat:1.5.0 \
				-b localhost:29092 \
				-t test-topic \
				-P

And in a separate terminal,

# consumer
docker run -it --network host edenhill/kafkacat:1.5.0 \
				-b localhost:29092 \
				-t test-topic \
				-C

Start/stop scripts

It’s inconvenient to use the individual commands every time we need to start a Kafka cluster for development and shutting it down and cleaning it up. Most people use Docker Compose for this, a reasonable solution from Docker. But I prefer using a plain old bash script with the individual commands over using Docker Compose. Because it’s more customizable and therefore more useful and it also makes one less thing to learn for me.

Here’s how my start and stop script looks like:

#!/bin/sh

echo "Creating network kafka-net.."
docker network create kafka-net

echo "Starting zookeeper.."
docker run -d --rm --network kafka-net -p 2181:2181 \
            --name zookeeper \
            -e ALLOW_ANONYMOUS_LOGIN=yes \
            bitnami/zookeeper:latest

echo "Starting kafka broker.."
docker run -d --rm --network kafka-net -p 9092:9092 \
            -p 29092:29092 --name kafka \
            -e ALLOW_PLAINTEXT_LISTENER=yes \
            -e KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181 \
            -e KAFKA_CFG_LISTENER_SECURITY_PROTOCOL_MAP=INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT \
            -e KAFKA_CFG_LISTENERS=INTERNAL://:9092,EXTERNAL://:29092 \
            -e KAFKA_CFG_ADVERTISED_LISTENERS=INTERNAL://kafka:9092,EXTERNAL://localhost:29092 \
            -e KAFKA_CFG_INTER_BROKER_LISTENER_NAME=INTERNAL \
            bitnami/kafka:2.5.0

echo "Printing all running docker containers.."
docker ps
#!/bin/sh

echo "stoping kafka.."
docker stop kafka

echo "stoping zookeeper.."
docker stop zookeeper

echo "stopping network kafka-net"
docker network rm kafka-net

Conclusion

As always, the code is available on my GitHub. The step to create the Kafka broker container can be repeated to create a cluster with multiple broker instances. The steps were tested on MacOS and Debian but they should also work under Windows. Hopefully this article should save some time if you are looking for an easy way to run Kafka in Docker for your development environment. And once you understand the steps, it’s easy to even customize it further to suit your requirements.

Here are a few references that might come handy:



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