Event-Driven Microservices for Distributed Systems

Microservice Architecture has proven its advantages over Monolithic Architecture. Many organizations are adopting Microservice Architecture & transforming their Monolithic project into Microservices.  Event-driven microservices is a new approach in microservice architecture. 

What is an Event? 

In layman’s terms, something that happens is nothing but an Event, and in software terms, state change is nothing but an Event. When you click the button with your mouse, it triggers a button-click event. 

Normally, microservices are written in a request-response fashion. Calling microservice endpoint as a request by expecting a response on it. This is a synchronous way to consume microservice. Here the caller must wait till the microservice responds. Waiting for something & holding all other actions till time is a major culprit in software performance. Event-Driven-Microservices is a solution for it. 

Event-driven microservices work in an asynchronous way. This approach decouples services from each other, making them more scalable, resilient, and easier to maintain. Below are the basic building blocks of it: 

  • Event Producer:
    • Microservices that trigger events are called event producers. 
    • They publish events to an event broker or messaging system. 
  • Event Broker: 
    • An event broker is a central component responsible for routing events from producers to consumers. 
    • It acts as a decoupling layer, allowing producers and consumers to be developed and deployed independently without needing to know about each other directly. 
  • Event Consumers:
    • Microservices that are interested in specific events are called event consumers. 
    • They subscribe to relevant events through the event broker. 
    • When an event is published, the event broker delivers it to all subscribed consumers.   

Let us discuss Event-Driven-Microservice with an example. Here, we have a Pizza delivery system

Event Driven Microservices

As shown in the diagram, this system follows an Event-Driven-Microservice architecture. It has a place-order service acting as an event producer. Rabbit MQ acting as an Event broker. Order-Executor & Order-Dispatcher are acting as both Event producer & consumer. Order-Status-Service acting as an event consumer. Here, no service is directly communicating with each other. All are communicating indirectly through event messages present in Rabbit MQ.  

Benefits of Event-Driven Microservices for Distributed Systems: 

  • Loose Coupling: Services are loosely coupled as they communicate through events, not direct calls. This makes them more independent and easier to maintain. 
  • Scalability: Services can scale independently. You can scale event producers and consumers based on their individual loads. 
  • Resilience: If one service fails, it does not necessarily bring down other services. Consumers can receive events again when the service recovers. 
  • Flexibility: New services can easily integrate by subscribing to relevant events. 
  • Responsiveness: Event-driven systems can be more responsive as communication is asynchronous. Consumers can process events at their own pace. 

Challenges of Event-Driven Microservices:

  •  Complexity: Event Broker is an additional building block introduced in Event-Driven microservices, so designing and implementing event-driven systems can be more complex than traditional architectures. 
  • Debugging: Event-driven is asynchronous in nature, so debugging is a big challenge. While working with multiple microservices, distributed tracing is needed to follow the flow of events across services for debugging purposes. 
  • Data Consistency: The possibility of data repetition is always an issue with microservices, so maintaining data consistency across services can require careful design and implementation strategies. 

Conclusion

Event-driven architecture is a powerful approach for building modern microservices applications; but again, you must choose it as per the nature of your project. It is mostly applicable in distributed kinds of systems (e.g. order & billing systems). To decide on an event-driven architecture, consider the complexity of your system, the communication patterns between services, and your team’s experience.