When developing microservices with NestJS, one of the most important concepts to master is the input/output (I/O) model, especially how to handle blocking and non-blocking operations. This decision directly impacts the scalability and performance of our applications.

✨ What is a Blocking Model?

A blocking model refers to operations that pause the flow of execution until a task is completed. This is common in processes like:

  • Database queries

  • External API calls

  • Disk write operations

In high-traffic systems, this behavior is risky, as a single thread can be held up waiting for a slow operation, preventing other requests from being processed.

🤔 Example of Blocking Code in NestJS 

@Post()
createUser(@Body() createUserDto: CreateUserDto) {
  const result = this.usersService.create(createUserDto); // Blocking if synchronous
  return result;
}

In this case, if create accesses the database synchronously, the server will wait for the response, halting other incoming requests.

✅ Non-Blocking Model (Recommended in NestJS)

NestJS is built on Node.js, which is designed for non-blocking I/O operations. This means we can execute long tasks (like database access) without stopping the main thread.

@Post()
async createUser(@Body() createUserDto: CreateUserDto) {
  const result = await this.usersService.create(createUserDto);
  return result;
}

Thanks to async/await, the request is only paused at that point, while the server continues handling other requests. This is the most efficient and scalable way to handle operations in NestJS.

✨ Benefits of the Non-Blocking Model

  • Higher performance under load
  • Improved scalability
  • Lower risk of timeouts
  • Better resource utilization

🚀 Best Practices

  • Use async/await for all I/O operations
  • Avoid blocking synchronous calls
  • Consider using queues (like RabbitMQ or Kafka) for heavy tasks
  • Use patterns like Circuit Breaker to handle slow external services

📄 Conclusion

In NestJS, mastering the non-blocking I/O model is essential for building efficient microservices. Whenever possible, choose asynchronous operations to maintain system flow and scalability. And if you have heavy tasks, consider offloading them to processing queues to avoid blocking the main thread.

Your server will thank you 🚀.