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Nowadays, more users yarn for interactive experiences. Instead of hitting the refresh button, they expect to be told if having something changed.

Receive notifications when someone likes your post on Instagram or one of your Facebook friends has just updated her/his status are examples of frontend applications reacting to events in the backend

This is made possible through event-driven APIs, which are supported through various modes of asynchronous event-driven communication between the client application and the backend.

So, as developers and architects, how should we handle asynchronous or event-driven communication in the world of APIs where synchronous communication is predominant and most firewalls block non-HTTP traffic?

It’s a matter of having an event-driven backend, choosing an asynchronous web API technology based on your exact async requirements, and a client that can work with remote events.

In this article, you will find helpful information about why even-driven APIs are worth adopting, which Asynchronous API Technology suits your purpose and tools for managing event-driven APIs.

When Should You Use Event-Driven API?

Event-enabling APIs is a relatively recent phenomenon compared to event-driven architecture (EDA), and it uses EDA to support scalable, real-time (or near-real-time), push-based communication in APIs published to third parties.

Being event-driven is about taking advantage of events as they happen, and consumers can register their interest (subscribe) and react to events in real time.

Making APIs event-driven or asynchronous (along with an underlying server-side event-driven architecture) can eliminate the need for inefficient polling requests and send updates to the client (event subscriber) as soon as they occur.

This provides a much better experience for users.

So, in a nutshell, event-enable APIs if:

  • The application should push changes from the server to the client rather than waiting for a client request.
  • The application must provide users with a highly active two-way communication channel.
  • The application requires many continuous interactions between the client and the backend that create scaling issues for the backend if synchronous APIs are used.
  • The application needs to be able to monitor system-wide events.
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Choosing an Asynchronous API Technology

Event-enabling APIs do come with multiple complexities — starting from what frameworks and networking protocols to choose, to building the reliability of delivery, and ensuring the scalability of a web-scale solution.

The asynchronous protocols commonly used today solve the problem of real-time communication, but they solve different aspects of this problem in different ways — thereby making some protocols serve different purposes better than others.

For multiplexed, bidirectional streaming and for applications that need a considerable amount of messages from both ends of the connection, WebSockets is ideal.

Server-Sent Events are especially useful in cases where a browser client is just interested in subscribing to a stream of data, without needing to communicate back with the server in the same connection.

Webhooks can be used for a simple implementation of pushing notifications to one or a small number of servers.

The newer async variants of GraphQL (Subscriptions and Live Queries) come with the benefits associated with GraphQL, however, the implementation is relatively complex and entails a considerable learning curve. gRPC and Kafka are generally used for communication between internal microservices.

What the Backend Architecture Should Look Like

While the client architecture must subscribe to state change events that originate from the backend, the typical backend architecture can be extended to create remote event connections with the clients via:

  • Event-driven APIs (ideally exposed through an API management platform that supports eventing semantics).
  • A message broker (if one is not already present).
  • Microservices that publish and process state change events.

Although event-driven APIs do not explicitly require a broker, using an intermediary between event producers and consumers helps to implement the required patterns to deliver more manageable and scalable solutions.

The broker receives events from IoT devices, change data capture (CDC) tools, other backend systems and services, and from client applications if two-way communication is enabled.

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It can then alert the services that subscribe to those events.

A scalable microservices architecture (MSA) is the optimal architecture for complex event-driven backend services.

These event-driven microservices can act as event subscribers or publishers to process events, handle errors, and persist event-driven states.

The remote event connection between the backend and web clients can be established through event-driven APIs powered by various asynchronous API technologies — such as Webhooks, WebSockets, Server-Sent Events, GraphQL subscriptions, etc.

The backend uses these APIs to send events pertinent to the clients and also receive events that originate from clients.

Managing Event-Driven API

An event-driven backbone will manage the overall real-time data flow securely and at scale, while asynchronous APIs can be managed for external and internal consumption with a traditional API management solution that comes with inherent or extended capabilities to support event-driven semantics.

Most organizations have basic event processing infrastructure, but many don’t have the capabilities to design, develop, test and manage event-centric APIs.

Essential API management capabilities — particularly governance, access control, monitoring, analytics, and monetization — provided by API management solutions can be used to manage asynchronous and REST APIs.

Some API management solutions already support Webhooks or/and Websockets.

Support for asynchronous APIs in API management tools gained traction with the AsyncAPI initiative standardizing event-driven APIs.

AsyncAPI is an open specification format similar to the Open API Specification, but focuses on asynchronous interfaces.

AsyncAPI is protocol-agnostic and lets you document how events are structured, their semantics, how consumers can subscribe, how events are delivered by a producer or consumer, and how endpoints are secured and authenticated.

A-high-level-backend-architecture-to-support-event-driven-APIs-alongside-synchronous-APIs.

A high-level backend architecture to support event-driven APIs alongside synchronous APIs.

Conclusion

Synchronous APIs are ideal for many scenarios — particularly if you need an instant response.

In other cases, when clients need to be informed of events or the processing required for the response happens at a different time, ordinary synchronous messaging becomes tricky and event-driven APIs can aptly address such needs.

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EDA is flexible enough that you can start with simple notifications, or combine two-way event communication with a synchronous approach to delivering an optimal architecture.

So, using an event-driven design alongside a traditional request/response design for your APIs brings the best of both worlds to build highly scalable and reactive web applications.

Furthermore, combining traditional API management capabilities with an event-driven architecture provides tremendous value additions to expand business reach and adoption.

About InApps

As the #1 software development company in Vietnam and #5 in Southeast Asia, we’ve gained valuable insights and experiences to help clients realize their projects.

At InApps technology, one of our core values is to be a business’s best companion. That’s why we keep sharing helpful content like this and listen thoughtfully to our customer’s demands and expectations before starting any project.

If you’re seeking solutions for your software development, you might want to learn more about us. Contact us for free, here!

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