An introduction to event-driven microservices

You can replace old monoliths with event-driven microservices. They facilitate the creation of flexible and scalable systems. This article explains how you can build microservices using event-driven techniques.

Definition of the problem with monolithic architectures

Legacy architectures are unable to meet the requirements of today’s constantly changing IT world. Modern applications should be durable, scalable, cloud-native and be able to function around the clock with an availability of as close to 100% as possible. Conventional architectures cannot cope with these requirements and obstacles. In order to meet these expectations, new technologies such as IoT, event hubs, cloud, machine learning and microservices have emerged. Event-driven microservices can help you replace obsolete monoliths with systems that are more flexible, scalable, and easier to manage.

What is an event-driven architecture?

Event-driven programming is not a new term; In fact, it is older than the software itself. You can take advantage of the event-driven architecture in microservices and serverless architectures. Event-driven architectures help you develop systems that are reliable, loosely connected, and scalable.

This type of design is both expandable and manageable. Event-driven architectures help in the development of systems with increased availability. If one of the components in an event-driven architecture model fails, the others can continue to operate normally. In contrast, in a typical monolithic application, failure of one component can cause failure of another.

Read: Serverless functions versus microservices

What is an event-driven microservice?

Microservices and event-driven computing have grown in popularity recently. Modern microservice designs are reactive and event-driven. This makes them loosely connected and easy to update and maintain. You can use event-driven microservices to build applications that are more adaptable and easier to maintain over time.

Consider the following scenario: You have numerous microservices that need to interact with each other asynchronously. You may want your services to be scalable, segregated, and managed independently. You may also want your microservices to generate events that other services can use. This is where event-driven microservices come into play. A microservice in an event-driven microservices architecture sends an event when an important action is taken or something remarkable occurs.

For example, when the status of an order changes, a service changes its data. Note that these events are subscribed to by the other microservices. It should be noted that both LinkedIn and Netflix use an event-driven, asynchronous communication architecture. Event-driven microservices can be used to carry out business transactions that involve many services. Let me illustrate this with an example.

Consider two services: notification and user. Assume that the notification service owns the notification table and the user service owns the user table. For example, suppose the notification service generated a notification with notification status “New” and published a “Notification Created” event. This event is processed by the e-mail service, the notification status is changed to “In progress”, and a “Send notification” event is published. The notification service then consumes the “Send notification” event and changes the notification status to “Processed”. This is a simple example of how event-driven services work asynchronously.

Event-driven microservices also help in the development of responsive applications. Let us understand this with an example. Look at the notification service we just talked about. For example, suppose the notification service needs to notify the user when a new notification is generated and queued. For example, suppose multiple users are trying to access the application at the same time and they know the notifications being processed.

In the event-driven model, all alerts are queued before being forwarded to the appropriate user. In this situation, the user does not have to wait while the notification (email, SMS, etc.) is processed. The user can continue to use the application while the notification is processed asynchronously. In this way, you can design your application to be responsive and loosely coupled.

Read: How to align your team with microservices

Challenges of event-driven microservices

While traditional applications are useful for a wide variety of use cases, they face challenges in terms of availability, scalability, and reliability. Typically, you have a single database in a monolithic application. Hence, it was difficult to support polyglot persistence.

Access to data in a microservices-based application is different. Each microservice usually has its own data, which means that the data controlled by a microservice is exclusive to it. When a service wants to access someone else’s data, it must do so through the API that that service can access.

Encapsulating the data in this way enables the creation of loosely coupled microservices that can be managed, maintained, and modified separately as needed.

When multiple services are accessing the same data, things get tricky. To make matters even more complicated, you may have microservices that use heterogeneous databases, that is, multiple types of databases. You may have microservices that use a combination of SQL and NoSQL databases, known as polyglot persistence.

Although multilingual persistence has several advantages, such as: For example, loosely connected services and improved efficiency and scalability also create significant problems in distributed data management.

One such problem is figuring out how to conduct business transactions that span multiple systems while maintaining data integrity. To ensure consistency in a typical monolithic application, you may want to use ACID transactions. However, translating this into a microservice application is not an easy task.

Read: Security challenges and solutions for the microservices architecture

Event-Driven Microservices Architecture Pattern

The following patterns are used in event-driven microservices development: Event Stream, Event Sourcing, Polyglot Persistence, and Command Query Responsibility Separation (CQRS).

The event streaming architecture publishes event streams to a broker using messaging technologies such as Apache Kafka and Confluent. Event streaming platform consumers can access and consume events from any stream.

Unlike traditional processing, event stream processing involves asynchronous processing of events in real time. As a result, event stream processing helps software components work together in real time in a decoupled and scalable manner.

Event sourcing is a popular architectural technique used in the transition from a monolith to a microservice. The application status is determined by a series of events in the Event Sourcing pattern. Like queues, events are displayed in the order they are received.

Polyglot Persistence is a strategy for storing data in heterogeneous databases. Let me illustrate this with an example. Data can be stored as a standalone service using the microservices architecture. You can also save data in various formats.

For example, if you’re developing an online ecommerce application, you might want a full text search. The database used by this search engine may be different from the relational database used by the e-commerce application (e.g. MongoDB or other document database to aid in quick searches). Your search engine and database should work together seamlessly. This coexistence of multiple storage formats is known as polyglot persistence.

The Command and Query Responsibility Segregation (CQRS) pattern is another paradigm that separates the reading and writing models. This architectural pattern separates read and write operations in an application. More specifically, the insert or update operations are usually handled by another service. You would also have a separate service for querying data. The CQRS pattern helps improve the performance, scalability, and security of your application.

Summary of the event-driven microservices

In this article, we discussed event-driven microservices and how to build your microservices using event-driven approaches. In an event-driven architecture, the publisher publishes an event and a consumer subscribes to it. These events help the services to communicate in a decoupled manner.

Read: Strategies for the success of microservices

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