How to start an event driven microservice backend application using Spring Kafka

Have you ever started a project from the start and it became a very large Project? 

As your application grows, the complexities to your code also grows. Even the once perfect, orderly project can turn into chaos because you constantly put more and more features, services and assets into the project, making maintenance a nightmare. 

One of the solutions to prevent a growing application from becoming a mess is by separating your application into smaller microservices. Microservice is a contrast to monolithic architecture, rather than putting your feature into one giant codebase, in microservice you divide your project into smaller projects(microservice), and then each microservice has only one responsibility with a specific task or functionality.

Here’s some feature what most application has that can be divided into microservices:

1. User authentication and user Management

Make your authentication and authorization of your APIs into different services, usually this type of service called Single sign on(SSO),  using some techniques like producing JWT tokens that can be used for authentication located on other services. Other than signing in, you can also put your user registration, user details and signing out combined in this service.

2. Website and app information

You can separate your company, web or app  information management into specific services, so that it makes it easier to maintain the code related to this feature. You can put features like managing pages, links, blogs in this type of microservice.

3. Product management Microservice

Whatever is related to the product must be handled by this microservice. This service provides APIs for listing, sorting, and product searching. Also handle the creation and updating of products.

4. Order Management

Processing and tracking orders can be isolated into a microservice. You can handle product checkout, order listing, order status updates, and related operations in this service.

5. Payment Gateway

Integration with external payment providers, managing transactions, and handling payment-related operations can be dedicated to this microservice.

6. Analytics and Reporting

Collecting and analyzing application usage data, generating reports, and providing insights can be performed by a separate microservice. This service aggregates and processes data, enabling businesses to gain valuable insights.

7. File Management

Handling image or file uploads, storage, retrieval, and serving can be abstracted into a dedicated microservice. You can utilize some cloud storage solutions or have your own storage infrastructure.

Microservice Spring and Kafka

When it comes to building scalable, maintainable backend systems, the Spring framework is one of the most popular choices not only in the Java ecosystem, but considered to be the perfect solution out of many frameworks in many programming environments.

In this article, we will develop a starting point on the journey of event-driven microservices using Kafka.

With Spring, you have the flexibility to choose the modules that best suit your needs. It provides seamless integration with various messaging systems, and one standout option is Kafka. Kafka is the right distributed streaming platform because Kafka is very excels at handling high-throughput, fault-tolerant, and scalable event streams.

This is a guide process step by step to start your Microservice in spring:

1. Setting Up Kafka Broker

First things first, we need to set up our development environment. Course you must have a kafka broker for your message streaming. Kafka broker is  a single instance of the Kafka server. It is just a running Kafka process that handles the storage of your message. Your kafka message is distributed into topics and then your message is consumed by a kafka group.

Best practice to set up a kafka for development is just by using Docker. Use this simple docker compose:

To run or start your Kafka broker for development, use the following docker command on the same folder where you put the docker-compose.yml:

docker-compose up -d

Open your docker, if you are seeing any Kafka broker in your docker container, it means that you have successfully run Kafka. Now that your kafka is running on your machine, let’s continue to configure it into your Spring project. 

So let's dive into the exciting part of coding our backend application development, with event driven microservice architecture.

2. Implementing Microservices with Spring Boot

With a kafka server running and a solid foundation about micro service provided above, it's time to get our hands dirty by starting to write our example microservice. We will be implementing the Product Microservice based on the chart above, a simple project consuming  product ID and producing and producing the ID to another topic.

To use Kafka in Spring-boot project, add Kafka in your maven dependency list.

And then set your kafka configuration inside application.yml, here’s an example of Kafka configuration in Spring boot, in the local machine, you can just use localhost. If you run Kafka on the server, change the bootstrap server with your server IP address.

Now comes to the Java part, integrating Spring Kafka into our microservices by writing  consumers and producers. In this example you will learn how to consume events within your microservices and how to publish events to Kafka topics, enabling seamless communication and event-driven behavior.

3. Testing

A robust backend application requires rigorous testing. In this tutorial I will provide you with a simple testing of our application. It will test the process of testing your event-driven microservices, ensuring that they perform as expected. Here’s how a simple  test can be written.

The above code is to test the processing of the kafka event method inside the MyKafkaService. When our application is running, processMessage will be triggered each time there’s an event coming into the productTopic.

In the next chapter we'll also discuss deployment strategies and best practices for scaling your system to handle increasing loads, so stay tuned.

This is just your first journey of event-driven microservices using Spring Kafka. Microservice means breaking down the application into smaller, independent services, you now maintain a project that has good levels of scalability and maintainability. With this new knowledge, you're well-equipped to the next level, I hope you can do more implementation of building scalable backend systems. Go fort and start building more amazing applications that you think will have a positive impact, but always remember that you must always love the process of building it.