How does event-driven architecture relate to microservices?

Event-driven architecture

Event-driven architecture (EDA) uses events to drive data and application behavior. It empowers applications to take action or respond to events with an event-driven architecture. As a result, clients receive data automatically when an event occurs within the application, which eliminates the need to request the server. In contrast to the traditional request-response model, the clients request the updated data periodically. Overall, EDA offers a more efficient and streamlined approach. A client must only subscribe to an event once and let the server send the events automatically whenever an update occurs.

The following diagram illustrates the difference between the EDA and the request-response model:

REST APIs vs. event-driven
REST APIs vs. event-driven

Microservices architecture

Microservices architecture structures applications as a collection of independent and loosely coupled services. Within it, each service can perform a specific function, which allows greater flexibility and agility. These services can be developed and scaled independently to provide better scalability, fault tolerance, and maintainability than monolithic architecturesIn monolithic architecture, an application is built as a single, unified and tightly coupled unit, with combining all components and functionalities..

Microservices architecture
Microservices architecture

However, implementing microservices architecture introduces distributed system complexities, inter-service communication, and monitoring challenges. Successful implementation requires proper design, governance, and infrastructure management.

Advantages and disadvantages of microservices architecture

In the subsequent section of this Answer, let's discuss how EDA mitigates some disadvantages of microservices architecture.

The synergy of EDA and microservices

EDA and microservices are related and mainly used to build loosely coupled and scalable systems. EDA enables asynchronous communication among microservices by implementing an event queue as an intermediary between them. When a service triggers an event, it is placed in the event queue, which broadcasts it to all connected services for consumption.

The following are some ways in which EDA relates to microservices:

Loose coupling

Both EDA and microservices architecture advocate for loose coupling between components. In an event-driven system, microservices communicate through events, empowering them to function independently and undergo modifications or replacements without impacting the entire system. The loose coupling fosters flexibility and agility that facilitates the development and evolution of microservices-based applications.

An example of loosely coupled services
An example of loosely coupled services

The services communicate with each other through an event queue.

Asynchronous communication

EDA encourages asynchronous communication between components, which aligns well with the asynchronous nature of microservices. Microservices can produce and consume events asynchronously, which decouples the timing and availability of services. This asynchronous communication pattern helps to handle varying workloads, prevent cascading failures, and improve scalability. However, asynchronous communication also introduces challenges like event ordering, eventual consistency, and ensuring reliable message delivery.

Scalability

Horizontal scalability is facilitated by event-driven architecture that enables the parallel processing of events across multiple microservices instances. This scalability is particularly significant in distributed systems as it empowers microservices to handle substantial event volumes autonomously. Moreover, event-driven systems exhibit resilience in the face of failures by offering mechanisms to retry or queue events. Therefore, this guarantees event preservation even during temporary service disruptions.

The vertical scaling of the system by adding a new microservice gets easier with EDA as compared to request-response models. The new microservice is connected to the event queue and can start generating or consuming new events. Moreover, all the connected services can communicate with this new integrated service.

An example of scaling microservices
An example of scaling microservices

Conclusion

Integrating EDA and microservices empowers developers to construct robust and adaptable systems that exhibit exceptional scalability, resilience, and loose coupling. Using event-driven communication, microservices gain the ability to function independently and respond promptly to changes or events within the system. This combined approach fosters agility, scalability, and fault tolerance, making it an ideal choice for constructing sophisticated distributed applications. By decoupling components and facilitating efficient communication through events, developers can unlock the full potential of microservices and meet the demands of modern, dynamic environments.

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