You can replace old monoliths by microservices that are event driven. They make it easier to create systems that are more flexible and scalable. This article discusses how you can create microservices using event driven techniques.
Defining the Problem with Monolithic Architectures
Legacy architectures are incapable of meeting the demands of today’s ever-changing world of IT. Modern applications should be durable, scalable, and cloud native, and should be able to function 24×7 with an uptime as near to 100% as feasible. Traditional architectures are incapable of meeting such demands and obstacles. To meet these expectations, new technologies such as IoT, Event Hubs, Cloud, Machine Learning, and Microservices have emerged. Microservices deployed in an event-driven fashion may assist you in replacing outdated monoliths with systems that are more flexible, scalable, and easy to manage.
What is an Event-driven Architecture?
Event-driven programming is not a new notion; in fact, it predates software itself. You can take advantage of event driven architecture in microservices and Serverless architectures. Event-driven architectures assist you in developing systems that are dependable, loosely connected, and scalable.
This kind of design is both extensible and manageable. Event-driven architectures aid in the development of systems with increased availability. If one of the components in an event-driven architectural model fails, the others may continue to work normally. In contrast, in a typical monolithic application, the failure of one component can cause the failure of another.
What is an Event-driven Microservice?
Microservices and event-driven computing have recently gained popularity. Modern microservices designs are reactive and event driven. As a result, they are loosely connected and simple to update and maintain. You may use event-driven microservices to create applications that are more adaptable and simpler to maintain over time.
Consider the following scenario: you have numerous microservices that must interact with one another asynchronously. You may want your services to be scalable, disconnected from one another, and independently maintained. You may also want your microservices to generate events that other services may consume. This is where Event-driven Microservices come into play. A microservice in an event-driven microservices architecture broadcasts an event when some important action is done or something noteworthy occurs.
As an example, when an order’s status is changed, a service changes its data. Note that those events are subscribed to by the other microservices. It should be noted that both LinkedIn and Netflix use event-driven, asynchronous communications architecture. Event-driven microservices may be used to execute business transactions that span many services. Let me illustrate this with an example.
Consider two services: Notification and User. Assume that the Notification Service has ownership of the Notification table, and the User Service has ownership of the User table. Suppose the Notification Service has generated a notification with the Notification Status “New” and published a “Notification Created” event. This event will be consumed by Email Service, the notification status will be changed to “Processing” and a “Send Notification” event will be 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 helps in the development of responsive applications as well. Let us understand this with an example. Consider the notification service we just talked about. Suppose the notification service needs to inform the user when a new notification is generated and stored in the queue. Assume that there are several concurrent users attempting to access the application and know the notifications that have been 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, text message, etc.) is being processed. The user can continue to use the application while the notification is processed asynchronously. This is how you can make your application responsive and loosely coupled.
Challenges of Event-Driven Microservices
Although traditional applications are useful for a variety of use cases, they face availability, scalability, and reliability challenges. Typically, you’d have a single database in a monolithic application. So, providing support for polyglot persistence was difficult.
Accessing data in a microservices-based application, on the other hand, is different. Each microservice normally owns its own data, implying that the data controlled by a microservice is exclusive to it. When one service wishes to access data held by another, it must do so using the API accessible by that service.
Encapsulating the data in this manner allows for the creation of loosely coupled microservices that may be managed, maintained, and altered separately as required.
When numerous services access the same piece of data, things get tricky. To complicate matters further, you may have microservices that utilize heterogeneous databases, i.e., multiple types of databases. You may have microservices that use a combination of SQL and NoSQL databases, which is referred to as polyglot persistence.
While polyglot persistence provides several advantages, such as loosely connected services and improved efficiency and scalability, it also brings significant distributed data management issues.
One such problem is figuring out how to perform business transactions that span several systems while maintaining data integrity. To ensure consistency in a typical monolithic application, you might want to use ACID transactions. However, putting this into practice in a microservices application is not an easy task.
Patterns of Event-Driven Microservices Architecture
The following patterns are utilized in the event-driven manner of developing microservices: Event Stream, Event Sourcing, Polyglot Persistence, and Command Query Responsibility Separation (CQRS).
Event Streaming architecture publishes streams of events to a broker using messaging technologies such as Apache Kafka and Confluent. Consumers of event-streaming platforms can access and consume events from each stream.
Unlike traditional processing, event stream processing entails the real-time processing of events asynchronously. As a result, event stream processing helps enable software components to collaborate in real-time in a decoupled and scalable way.
Event Sourcing is a popular architectural technique that is utilized while transitioning from a monolith to a microservice. The application state is determined by a series of events in the Event Sourcing pattern. Like queues, events are presented in the order they were received.
Polyglot Persistence is a strategy used to store data in heterogenous databases. Let me illustrate this with an example. Data may be stored as a distinct service using the microservices architecture. You may also save data in a variety of formats.
For instance, if you are developing an online e-commerce application, you may want a full text search capability. The database utilized by this search engine may be different from the relational database used by the e-commerce application (for example, MongoDB or any other document database for supporting rapid searches). Your search engine and its database should work together seamlessly. This coexistence of several storage formats is known as Polyglot persistence.
The Command and Query Responsibility Segregation (CQRS) pattern is yet another paradigm that separates the read and write models. This architectural pattern separates read and write operations in an application. To be more specific, the insert or update operations are usually handled by a different service. For querying data, you would additionally have a separate service. The CQRS pattern helps enhance performance, scalability, and security of your application.
Summary of Event Driven Microservices
In this article we have 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.