Node.js Architecture: Understanding Core Components with Diagram

Think of a chat app with millions of users sending typed messages every second or a streaming service pushing live data around the world. How can a server handle millions of requests without crashing or slowing down performance?
This is where Node.js comes into play. Node.js is built on Google’s V8 engine and event-driven, non-blocking architecture, changing the way we build scalable, high-performance applications. In this blog, we will explain Node.js architecture, its event loop, along with the thread pool, and show you why every developer should be using it for modern web development. So let’s start with web applications for the basics!

Table of Contents:

• Web Applications in Node.js Architecture
• What is NodeJS Architecture
• Single-Threaded Event Loop Architecture in Node.js
• Node.js Architecture Diagram
• Core Components of NodeJS Architecture
• Workflow of Node.js Server Architecture
• Advantages of Node.js Server Architecture
• Disadvantages of Node.js Server Architecture
• Best Practices for Node.js Application Architecture
• What Makes Node.js Application Architecture the Right Choice for Applications
• Node.js Architecture vs Other Server Architectures

Web Applications in Node.js Architecture

A web application is simply software that runs on some sort of server, rendered by some sort of client (the browser or app) that accesses all of your application’s resources via the Internet. There are three main layers in a web application.

• Client (Front-End) – The client is the layer where users interact with the application via a browser or mobile app. Clients can send requests (submitting a form, logging in, fetching data, etc.) to the server.
• Server (Back-End) – The server, as the name implies, is the area that will receive requests from clients, perform tasks automatically, and return results to those clients. The server allows the client to perform operations on data that was stored and is later retrieved through the web application front-end. Node.js has a very efficient event-driven, non-blocking architecture that doesn’t block the event loop for multiple requests, as it doesn’t create a new thread for each request.
• Database (Storage Layer) – A database is where the data used in a web application resides. The data stipulated in the request can be created, modified, and deleted. Node.js is able to use both SQL and NoSQL type databases (MySQL, MongoDB) seamlessly and usually uses asynchronous queries to ensure good performance.

These three elements together serve as the building blocks for any contemporary web application. Node.js fits into the server layer, it has a lightweight and scalable architecture, and it is suitable for applications that require real-time processing, like chats, online gaming, streaming, and APIs, without sacrificing performance – even under heavy contention.

What is NodeJS Architecture?

At the most basic level, Node.js implements a Single-Threaded Event Loop Architecture. Rather than create a new thread for each new request (like Java or .NET does), Node.js handles all requests on a single thread using an event loop with a background thread pool (managed by libuv).
This allows Node.js to handle multiple requests from clients at the same time, while waiting for requests to fully complete, in a non-blocking mode, which is perfect for I/O bound processing.

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Single-Threaded Event Loop Architecture in Node.js

Node.js is a single-threaded, event-driven architecture. Node.js is based on two basic components of software: Node.js “runtime”, which consists of everything you need to create an event loop, and the “libuv” library, which is a C library responsible for managing the event loop, thread pool, and asynchronous I/O operations. Let’s examine these in detail:

Node.js is Single Threaded Event Loop

The event loop of Node.js is running on a single main thread, which means all the tasks being processed happen in one place, instead of spawning multiple threads for each request. All requests can have a synchronous task (which is executed right away) and a part of an asynchronous task (which would have a delay, such as reading a file, querying a database, or performing some encryption), or both of these.
The event loop processes synchronous tasks one by one, immediately after the previous task completes. If the event loop reaches an asynchronous task, the event loop would not block the main thread. There would be a couple of options to handle asynchronous tasks: either schedule them with libuv’s timers and queues, or offload to a thread pool (only for file I/O, crypto, and DNS) so as not to block the main thread while continuing to process other tasks in the queue. This way, the main thread can take up the synchronous part of new requests, while the asynchronous part of the request is processed in the background.

Example Code:

const fs = require('fs');

console.log("1️⃣ Start");

// Synchronous code
for (let i = 0; i < 2; i++) {
  console.log(`2️⃣ Sync loop iteration ${i}`);
}

// Asynchronous timer (macrotask)
setTimeout(() => {
  console.log("3️⃣ setTimeout callback (macrotask)");
}, 0);

// Promise (microtask)
Promise.resolve().then(() => {
  console.log("4️⃣ Promise resolved (microtask)");
});

// Asynchronous file read (delegated to libuv thread pool)
fs.readFile(__filename, 'utf8', () => {
  console.log("5️⃣ File read complete (I/O callback from thread pool)");
});

console.log("6️⃣ End");

Output:

1️⃣ Start
2️⃣ Sync loop iteration 0
2️⃣ Sync loop iteration 1
6️⃣ End
4️⃣ Promise resolved (microtask)
3️⃣ setTimeout callback (macrotask)
5️⃣ File read complete (I/O callback from thread pool)

Node has Non-Blocking I/O Model

In traditional systems an input/output (I/O) operations like reading files, querying a database, or calling an API are blocking. This means the program must wait for a task to finish before moving on to the next task. If something takes a long time, then everything gets delayed.
Unlike traditional systems, Node.js uses a non-blocking I/O model that prevents the main thread from being blocked. It offloads the heavy-lifting asynchronous task(s) to a background thread (called the libuv thread pool). Once the background / libuv thread finishes the async task(s), it notifies the main thread to continue execution, either the callback or promise code. Thus, while the async operation is performing I/O, the main thread is not blocked at all. This is why Node.js has become very popular for developing real-time apps like chat apps, streaming platforms, APIs, etc.

Example Code:

const fs = require('fs');

console.log("1️⃣ Start");

// Blocking I/O (synchronous)
const data = fs.readFileSync('example.txt', 'utf8');
console.log("2️⃣ Blocking read:", data);

// Non-blocking I/O (asynchronous)
fs.readFile('example.txt', 'utf8', (err, result) => {
  if (err) throw err;
  console.log("4️⃣ Non-blocking read:", result);
});

console.log("3️⃣ End");

Suppose example.txt contains Hello Node.js Intellipaat

Output:

1️⃣ Start
2️⃣ Blocking read: Hello Node.js Intellipaat
3️⃣ End
4️⃣ Non-blocking read: Hello Node.js Intellipaat

Event-Based, Instead of Waiting for I/O Operation

Node.js handles I/O tasks without blocking the main thread using an event-driven architecture. When an async task starts (e.g., file read, DB query), Node.js sends it to the libuv thread pool or OS APIs instead of waiting for it to complete. When the I/O work is done, libuv notifies the event loop that work has been completed, and the appropriate callback or promise resolution is added to the event queue. The event loop picks it up in its next turn in the overall cycle, keeping the main thread non-blocking and responsive. Node.js’s architecture can handle a large number of concurrent connections with very little overhead, making it suitable for I/O-oriented and real-time applications.

Example Code:

const fs = require('fs');
const EventEmitter = require('events');

// Create an event emitter
const emitter = new EventEmitter();

console.log("1️⃣ Start");

// Register an event listener for "fileRead"
emitter.on("fileRead", (content) => {
  console.log("3️⃣ Event received: File content ->", content);
});

// Start an async I/O operation
fs.readFile("example.txt", "utf8", (err, data) => {
  if (err) throw err;

  // Instead of blocking, emit an event when the file is ready
  emitter.emit("fileRead", data);
});

console.log("2️⃣ End (Node.js did not wait for file read!)");

Output:

1️⃣ Start
2️⃣ End (Node.js did not wait for file read!)
3️⃣ Event received: File content -> Hello Node.js Intellipaat

Node.js Architecture Diagram

Now, let’s understand each part of the Node.js architecture and the workflow of a web server developed using Node.js.

Core Components of NodeJS Architecture

1. Requests: Depending on the actions that a user needs from the server, requests can either be blocking (complex) or non-blocking (simple).
2. Node.js Server: This is simply a server that accepts requests from the user, processes them, and returns results to the user.
3. Event Queue: The Event Queue is your FIFO temporary storage for incoming client requests. It controls the sequential pass of the requests to the Event Loop when it has the capacity.
4. Thread Pool: The Thread pool on a Node.js server is the available threads to perform operations required to process requests.
5. Event Loop: The Event Loop accepts requests from the Event Queue and sends responses out to the clients.
6. External Resources: External resources are used to handle blocking client requests. External resources can be anything (computation, storage, etc.).

Workflow of Node.js Server Architecture

A web server developed using Node.js typically has a workflow that is quite similar to the diagram illustrated below. Let’s explore this flow of operations in detail.

Clients send requests to the web server to interact with the web application. Requests can be non-blocking or blocking:

• Querying for data
• Deleting data
• Updating the data

Node.js picks up the incoming requests and pushes them onto the Event Queue.
The requests are then relayed through the Event Loop one at a time.
The Event Loop examines whether the requests are simple enough not to require any external resources.
The Event Loop performs simple requests (non-blocking operations) like I/O Polling and returns the responses to the appropriate clients.
One of the threads in the Thread Pool will be assigned to each complex request.
This thread will complete a single blocking request. It will be consuming the external resources such as compute, database, file system, etc.
When the task is complete, the thread returns the result to the Event loop, and it will trigger the callback function to send the response back to the client.

Advantages of Node.js Server Architecture

1. Node.js server can handle a high number of requests efficiently through an Event Queue and Thread Pool.
2. Instead of creating a thread for each request like traditional servers, Node.js uses an event loop, which optionally uses a thread pool, totally increasing the server’s context, allowing for multiplexing of I/o operations throughput.
3. The entire process of serving requests to a Node.js server consumes fewer memory and server resources, as requests are handled one at a time.

Disadvantages of Node.js Server Architecture

1. It is limited to one thread only, which means it can be a bottleneck for CPU-intensive tasks.
2. The complex nesting of callbacks can result in hard-to-maintain code.
3. Not good for heavy tasks, since it is built on a non-blocking I/O model.
4. Heavy reliance on third-party libraries can cause unforeseen stability or security issues.
5. Frequent API changes can lead to backward compatibility issues.
6. JavaScript’s lack of strong typing contributes to unexpected runtime errors and bugs.

Best Practices for Node.js Application Architecture

1. Adopt the Publish and Subscribe Model
   In the pub/sub model, publishers can publish messages to channels without knowing which clients they are sending the messages to, and subscribers can listen to the messages without knowing which clients they are receiving the messages from. When using a message broker, clients can exchange messages even if they are offline (subscribers can check for new messages until they are up to date with the latest from a publisher). Using this model makes applications that are decoupled, scalable, and efficient for real-time communication.
2. Adopt a Layered Approach
   Create a Layer of Controllers, Services, and Data access. Layered architecture improves code quality, debugging, and scalability while keeping background processes manageable.
3. Make Use of Dependency Injection
   Dependency injection will decrease the tight coupling between modules and make it easier to test, maintain, and extend the system.
4. Use Third-party Solutions
   Instead of reinventing the wheel, utilize some well-known third-party packages (e.g., Passport.js for authentication, Winston for logging, Joi for validation, etc.), which can save you development time and provide assurance that best practices are being implemented.
5. Use a Consistent Folder Structure
   A simple folder structure (e.g., routes, controllers, services, models, etc.) allows the application to be maintained, scalable, and collaborative, especially with larger teams.
6. Use Linters, Formatters, Style Guides, Comments
   Utilize tools such as ESLint, Prettier, and JSDoc to promote clean coding standards. When coding style is consistent and meaningful comments are used, it promotes better code readability and may lessen the number of bugs.
7. Fixing Bugs with Unit Testing, Logging, and Error-handling
   The addition of unit testing (Mocha, Jest), logging (Winston, Morgan), and structured error-handling middleware promotes early bug detection, better debugging, and a more robust application.
8. Use of Config File and Environment Variables
   Make sure you keep sensitive credentials and environment-specific settings in .env files or config services so that it improves security and creates a better deployment experience in other environments.Enable HTTP compression (Gzip/Brotli)
   Enable Gzip compression for API responses to reduce payload size, improving speed and performance, especially for applications handling large data or high traffic.

What Makes Node.js Application Architecture the Right Choice for Applications?

Node.js is the best because it is a non-blocking and event-driven architecture and is lightweight, fast, and scalable. Plus, Node.js manages concurrent requests in a non-blocking way, so it is perfect for any real-time applications, chats, streams, and APIs.

Node.js Architecture vs Other Server Architectures

Node.js operates on a single-thread event loop and asynchronous I/O instead of a traditional multi-threaded architecture (like Java, .NET, Python). This allows Node.js to provide more requests with fewer resources; thus, making it better for I/O-heavy applications and others better for CPU-heavy applications.

Conclusion

Node.js has changed the way we build modern apps. With its single-threaded event loop, non-blocking I/O, and lightweight runtime, it can handle thousands of requests at once without eating up too many resources. That’s why it’s perfect for real-time apps like chats, streaming platforms, APIs, and collaborative tools. Sure, it’s not the best for heavy CPU tasks, but if you follow good practices like using a layered design, dependency injection, and reliable third-party tools, you’ll end up with apps that are scalable, easy to maintain, and high-performing.

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Node.js Architecture – FAQs