Building Synchronous or Asynchronous APIs

When developers, engineers or architects start analyzing a new software solution, it is common to be faced with the decision of whether to build synchronous or asynchronous APIs. Which is the correct way?

I will talk more about this, but let me tell you in advance: the answer is: it depends. Why? Because we must consider a series of factors.

The great challenge of modern applications and even of the modern world is that we want everything right away, whether it is an order on a delivery app, making a purchase or loading a news story, for example, everything needs to be fast. This directly affects how we design software and the ability to handle multiple tasks simultaneously is crucial for application performance.

APIs are like building blocks, essential in software development. In this article, I will explore some of the differences between synchronous and asynchronous APIs, their pros and cons, and how to choose the most appropriate approach for your projects.

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How Synchronous APIs Work

A synchronous API operates sequentially: the request is made, the code waits for the response, and only after receiving the response does the next code execute. It's like asking a question and waiting patiently for the answer before continuing the conversation.

Pros:

• Simplicity: The synchronous model is easier to understand and implement, since the execution flow is linear.

• Debugging: Errors are easier to identify and debug, since the code is executed sequentially.

Cons:

• Thread blocking: While a synchronous API waits for the response, the thread that called it is "blocked", preventing other tasks from being executed.

• Low performance: In scenarios with many I/O (input/output) operations, such as calls to databases or external services, synchronous APIs can lead to significantly lower performance.

• Limited Scalability: Applications with high concurrency may suffer from scalability issues when using synchronous APIs, since the number of available threads is limited.

Asynchronous APIs

An asynchronous API, on the other hand, allows the code to continue executing while the asynchronous operation is in progress. It is like asking a question and continuing to work on other tasks while waiting for the answer.

Pros:

• High performance: Asynchronous APIs allow the thread to continue working on other tasks while the asynchronous operation is being performed, improving performance, especially in I/O operations.

• Scalability: Applications with high concurrency can scale better with asynchronous APIs, since fewer threads are needed to handle a larger number of requests.

• Better user experience: In applications with a graphical interface, asynchronous APIs help prevent the interface from freezing while time-consuming operations are being performed.

Cons:

• Complexity: The asynchronous model can be more complex to understand and implement, especially for less experienced developers.

• Debugging: Errors in asynchronous code can be more difficult to identify and debug, since the flow of execution may be less obvious.

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Comparison between Synchronous and Asynchronous APIs

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Table comparing characteristics of synchronous and asynchronous APIs

When to use each approach?

Synchronous APIs:

• Simple and fast operations.

• Critical code that cannot be interrupted.

• Scenarios where simplicity is more important than performance.

Asynchronous APIs:

Time-consuming I/O operations (databases, web services).

Applications with high concurrency.

Scenarios where performance and scalability are priorities.

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Conclusion

The choice between synchronous and asynchronous APIs depends on the specific needs of each application. In general, and in my opinion, asynchronous APIs are the best option for most modern scenarios, as they offer better performance, scalability, and user experience. However, synchronous APIs can still be useful in many cases, for example, in applications with specific scopes, some monoliths, and microservices.

This article presents an overview of synchronous and asynchronous APIs, their concepts, and applications in software development, but for a deeper understanding, I recommend also analyzing the technology that will be used.

Best regards and see you next time!