In this article we provide a step-by-step guide to getting started with MigratoryData KE (Kafka Edition), an ultra-scalable Websocket publish/subscribe broker which integrates natively with Apache Kafka. Thanks to its huge vertical scalability (1000x more scalable than the C10K problem) and linear horizontal scalability both for publishers and subscribers, MigratoryData KE can enable bidirectional messaging communication between Apache Kafka and millions of Web and Mobile users or IoT devices - and do so cost-effectively.

Topics and Subjects

We’ve already explained why MigratoryData is a perfect fit for extending Apache Kafka to the Internet, reliably and at scale, as well as the compatibility and complementarity between the two messaging systems.

It is sufficient to say here that both systems MigratoryData and Kafka are publish/subscribe messaging systems, both using a similar notion - named topic in Kafka and subject in MigratoryData - to connect subscribers and publishers. Both Kafka topics and MigratoryData subjects are strings of characters with the following restrictions:

  • A Kafka topic can be any string of up to 255 of the following ASCII characters a-z, A-Z, 0-9, . (dot), _ (underscore), and - (dash), e.g. vehicles
  • A MigratoryData subject can be any string starting with / (slash), and consisting of one or more substrings of any UTF-8 characters excluding / (slash), named segments, separated between them by / (slash), e.g. /vehicles/car1/speed

Topics/Subjects Mapping

We use a simple convention to dynamically map between Kafka topics and MigratoryData subjects. The first segment of the MigratoryData subject corresponds to a Kafka topic, and the remaining segments of the subject correspond to a Kafka key. Therefore, in MigratoryData KE, the first segment of a subject, corresponding to a Kafka topic, must use at most 255 of the following ASCII characters permitted by the Kafka topics, i.e. [a-zA-Z0-9_-]. The subsequent segments of the subject, corresponding to a Kafka key, can use any UTF-8 characters as there are no restrictions for the keys in Kafka.

For example, the following MigratoryData subject /vehicles/car1/speed corresponds to the Kafka topic vehicles and the Kafka key car1/speed as illustrated here:

drawing

Because in Kafka it is possible to publish a message on a topic, say vehicles, without using a key, i.e. using a null key, then the Kafka topic vehicles corresponds to the MigratoryData subject /vehicles, consisting only of the first segment without using any subsequent segments:

drawing

Installing Kafka and MigratoryData KE

MigratoryData KE comes with installers for Linux and instructions on how to deploy in production MigratoryData KE clusters either on premises or in the cloud, using Docker and Kubernetes. Also, a platform-independent tarball useful for development and testing on platforms like Linux, Windows, MacOS is available.

Apache Kafka is available from production-ready cloud services like Confluent or Azure Event Hubs. Also, a platform-independent tarball useful for development and testing on platforms like Linux, Windows, MacOS is available.

The only requirement both for MigratoryData and Apache Kafka is to have installed Java Runtime Environment (JRE) version 8.

Deploying Kafka

Make sure that you have Java version 8 installed. Download the platform-independent tarball package of Apache Kafka and unzip it to any folder, change to that folder, and run the following two commands in two different terminals on Linux or MacOS (run the similar commands with the bat extension instead of the sh extension on Windows):

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

This will deploy a cluster of one instance of Apache Kafka which will listen for Kafka producers and consumers on localhost, on the default port 9092.

Deploying MigratoryData KE

Make sure that you have Java version 8 installed. Download the platform-independent tarball package of MigratoryData KE and unzip it to any folder, change to that folder, and run the following command on Linux or MacOS (run the similar command with the bat extension instead of the sh extension on Windows):

./start-migratorydata-ke.sh

This will deploy a cluster of one instance of MigratoryData KE which will listen for client connections on localhost, on the default port 8800.

The default configuration of MigratoryData KE contains a group of Kafka consumers with a single consumer connecting to the Kafka cluster deployed at the address localhost:9092, and subscribing to the Kafka topic vehicles as you can find in the configuration file kafka/consumer.properties:

bootstrap.servers=localhost:9092
topics=vehicles
consumers.size=1

Also, the default configuration of MigratoryData KE contains a group of Kafka producers with a single producer connecting to the Kafka cluster deployed at the address localhost:9092, as you can find in the configuration file kafka/producer.properties:

bootstrap.servers=localhost:9092
producers.size=1
Note the asymmetry between the default configuration files of the Kafka producer and Kafka consumer implemented into MigratoryData KE.

On one hand, the Kafka consumer includes a supplementary parameter topics, meaning that an Internet client of MigratoryData KE will be able to subscribe only to the subjects having as the first segment, the Kafka topic vehicles, e.g. /vehicles/car11/temperature, /vehicles/car1/speed, etc - provided however that the Internet client is entitled by your authorization rules to subscribe to those subjects. Multiple Kafka topics can be configured with the parameter topics as a comma-separated list.

On the other hand, an Internet client of MigratoryData KE will be able to publish to any Kafka topic, without the need to configure any parameter. For example, a message on the subject /trucks/t1/location published by an Internet client will be automatically sent to the Kafka cluster on the topic trucks with the key t1/location, provided that the Internet client is entitled by your authorization rules to publish on the subject /trucks/t1/location.

Testing

MigratoryData KE Messaging

At this stage, you can open the demo web application built with MigratoryData SDK for JavaScript and bundled with MigratoryData KE as follows. Start a web browser on the machine where you have installed MigratoryData KE and Kafka and open the following URL:

http://localhost:8800

If a browser is not available on the machine where you installed MigratoryData KE and Kafka, then, supposing the address of the machine is push.example.com and the port 8800 is not blocked by the firewall, you can remotely test the installation by opening the following URL from a remote machine: http://push.example.com:8800

This will open the welcome page of MigratoryData KE which contains certain docs and demos. Click on the DEMO button of the welcome page. You should see a web page like the following one:

drawing

Supposing you installed MigratoryData KE and Kafka on your machine, click on the Connect button to connect the demo application to your deployment. Otherwise, if you installed MigratoryData KE and Kafka on a remote machine, say http://push.example.com:8800, change the Location in the demo app to http://push.example.com:8800 before clicking on the Connect button.

Subscribe, to the subject /vehicles/1/speed by clicking the Subscribe button. You can also subscribe and unsubscribe to and from other subjects.

Finally, publish some messages on the subject /vehicles/1/speed by clicking on the Publish button. You should see how these messages are received in real-time. Also, you can open the demo app in another browser to see that, in fact, the messages are delivered from the backend to all subscribers of that subject.

Kafka Messaging

By opening a Kafka consumer on the topic vehicles you will see that the messages published by the demo web app on the subject /vehicles/1/speed are automatically received by Kafka on the topic vehicles with the key 1/speed as follows:

./bin/kafka-console-consumer.sh --topic vehicles \
--bootstrap-server localhost:9092 \
--consumer.config config/consumer.properties \
--property print.key=true \
--from-beginning
1/speed	100
1/speed	102

Also, you can produce messages to Kafka on the topic vehicles with the key 1/speed and see them arriving to your web application automatically and in realtime as follows:

./bin/kafka-console-producer.sh --topic vehicles \
--bootstrap-server localhost:9092 \
--producer.config config/producer.properties \
--property "parse.key=true" \
--property "key.separator=:"
>1/speed:88
>1/speed:90
>1/speed:99

Conclusion

This was a quick introduction to MigratoryData KE. Please refer to the Architecture Guide, Configuration Guide, and Installation Guide to learn more about MigratoryData KE. Then, start building your realtime web and mobile apps or IoT project using your preferred programming languages to communicate with your MigratoryData KE cluster and your Kafka ecosystem. Please refer to the documentation of the MigratoryData Client SDKs and MigratoryData Plugin SDKs for your preferred programming languages.