Siva Samanthapudi

Posted on Aug 9

React Mastery Series – Day 31: Advanced React Architecture – Designing Large-Scale Applications

#react #reactjsdevelopment #webdev

Welcome back to the React Mastery Series!

We've completed the first 30 days of our React journey.

So far, we've covered:

React Fundamentals
Components & Props
Hooks
Context API
Redux Toolkit
API Integration
Forms & Validation
Performance Optimization
Testing
Authentication & Authorization
Design Patterns
Error Handling
Enterprise Project Structure

Now it's time to move from:

"How do I build a React application?"

to:

"How do I architect a React application that can scale?"

This is where the responsibilities of a Senior Frontend Engineer / Frontend Architect begin.

What Does "Large-Scale React Application" Mean?

A small React application might have:

10–50 Components
5–10 Pages
2–3 Developers

A large enterprise application might have:

1000+ Components
100+ Pages
Multiple Business Domains
Multiple Teams
Multiple APIs
Multiple Environments
Millions of Users

At this scale, writing good components isn't enough.

We need a clear architecture.

The Architecture Problem

Imagine a banking application containing:

Accounts
Cards
Payments
Loans
Investments
Transactions
Notifications
Customer Support

If every feature can directly access everything else:

Accounts
   ↕
Payments
   ↕
Cards
   ↕
Loans
   ↕
Investments

The application eventually becomes tightly coupled.

One feature starts depending on another.

Changes become risky.

The Goal of Architecture

A good architecture should provide:

Low Coupling
      +
High Cohesion
      +
Clear Boundaries
      +
Reusable Components
      +
Testability
      +
Scalability

Let's understand each one.

1. High Cohesion

Code that belongs together should stay together.

For example:

features
└── payments
    ├── components
    ├── hooks
    ├── services
    ├── types
    └── utils

Everything related to payments is located inside the payments domain.

This is high cohesion.

2. Low Coupling

Features shouldn't unnecessarily depend on each other's internal implementation.

Bad:

Payments
   ↓
Accounts Internal Component
   ↓
Accounts Internal Service

Better:

Payments
   ↓
Accounts Public API

The payments feature only knows what it needs to know.

Public APIs Between Features

One useful technique is to expose only the functionality that other features need.

Example:

accounts
├── components
├── hooks
├── services
├── types
└── index.ts

The index.ts acts as a public entry point.

export { AccountSummary } from "./components/AccountSummary";
export { useAccounts } from "./hooks/useAccounts";
export type { Account } from "./types";

Other features can import from:

import {
  AccountSummary,
  useAccounts,
} from "@/features/accounts";

Instead of reaching into internal files:

import { AccountSummary } from "@/features/accounts/components/internal/AccountSummary";

This creates a clear boundary.

Feature-Driven Architecture

A large React application can be organized around business domains.

src
├── app
├── features
│   ├── auth
│   ├── accounts
│   ├── cards
│   ├── payments
│   ├── loans
│   └── investments
├── shared
├── layouts
└── routes

This is often easier to scale than organizing everything by technical type.

Layered Architecture Inside a Feature

A feature can also have internal layers.

payments
├── components
├── hooks
├── services
├── store
├── types
├── validation
└── utils

Each layer has a responsibility.

Components

UI and presentation.

Hooks

Reusable React behavior.

Services

Communication with APIs and external systems.

Store

Feature-specific state.

Types

TypeScript models.

Validation

Input and business validation rules.

Utils

Pure helper functions.

Clean Architecture Concepts

Clean Architecture separates business rules from infrastructure.

A simplified React interpretation looks like:

UI Layer
   ↓
Application Layer
   ↓
Domain Layer
   ↓
Infrastructure Layer

Let's understand this.

UI Layer

Responsible for:

Rendering
User interactions
Navigation
Visual states

Example:

function PaymentForm() {
  const { submitPayment, isSubmitting} = usePayment();

  return (
    <form onSubmit={submitPayment}>
      {/* Form UI */}
    </form>
  );
}

The component shouldn't know how the backend works.

Application Layer

This layer coordinates application behavior.

Example:

function usePayment() {
  const submitPayment = async ( payment: PaymentRequest) => {
    return paymentService.createPayment(payment);
  };

  return {submitPayment};
}

The hook coordinates the UI with the underlying services.

Domain Layer

The domain contains business concepts and rules.

For example:

type Payment = {
  amount: number;
  currency: string;
  accountId: string;
};

Business rules might include:

function canMakePayment( balance: number, amount: number) {
  return balance >= amount;
}

This logic shouldn't depend on React.

Infrastructure Layer

This layer communicates with external systems.

Examples:

REST APIs
GraphQL
Browser storage
Analytics
External SDKs

Example:

export async function createPayment(payment: PaymentRequest) {
  const response = await api.post("/payments",payment);
  return response.data;
}

Why Separate These Layers?

Imagine the backend changes from:

REST API

to:

GraphQL

If API implementation is isolated:

UI
 ↓
Application
 ↓
Domain
 ↓
GraphQL Service

We can replace the infrastructure without rewriting the entire UI.

That's the power of separation of concerns.

Dependency Direction

A key architectural principle is:

Dependencies should point toward stable business logic.

Instead of:

Component
   ↓
Axios
   ↓
API
   ↓
Business Rules

Prefer:

UI
 ↓
Application
 ↓
Domain

Infrastructure
 ↓
Implements External Communication

This makes business logic easier to test.

Dependency Injection Concept

React doesn't have traditional dependency injection like Angular.

However, we can implement similar concepts using:

Props
Context
Factory functions
Interfaces
Provider patterns

For example:

type PaymentService = { createPayment: (
    payment: PaymentRequest
  ) => Promise<Payment>;
};

The hook can receive the service:

function createPaymentController(service: PaymentService) {
  return {
    submitPayment: (
      payment: PaymentRequest
    ) => service.createPayment(payment),
  };
}

Now testing becomes easier because we can inject a mock service.

Testing Becomes Easier

Without separation:

Component
   ↓
Axios
   ↓
Backend

Testing requires mocking multiple dependencies.

With separation:

Component
   ↓
Controller
   ↓
Interface
   ↓
Mock Service

We can test business behavior without making real network requests.

State Management Architecture

Not every piece of state belongs in Redux.

A useful rule is:

Local State

Use for:

Modal visibility
Input values
Temporary UI state

Context

Use for:

Theme
Authentication
Localization

Server State

Use tools such as:

TanStack Query

for:

API data
Caching
Refetching
Synchronization

Global Client State

Redux Toolkit can be useful for:

Complex shared application state
Cross-feature workflows
Client-side business state

Don't Put Everything in Redux

A common architectural mistake is:

Everything
   ↓
Redux

This creates unnecessary complexity.

Instead:

UI State
   ↓
useState

Shared Context
   ↓
Context API

Server State
   ↓
TanStack Query

Complex Global State
   ↓
Redux Toolkit

Choose the simplest appropriate tool.

Shared Components

Enterprise applications usually have a design system.

Example:

shared
└── components
    ├── Button
    ├── Input
    ├── Modal
    ├── Table
    ├── DatePicker
    └── Notification

These components should be:

Reusable
Accessible
Consistent
Well tested

Don't Put Business Logic in Shared Components

A shared Button shouldn't know about payments.

Bad:

<Button
  onClick={submitPayment}
  paymentType="INTERNATIONAL"
  accountId={accountId}
/>

The button should only care about being a button.

Business logic belongs in the feature.

Domain Boundaries

Think about each feature as a small business domain.

Payments
     │
     ├── Payment Form
     ├── Payment API
     ├── Payment Validation
     └── Payment State

The payments domain owns its own logic.

This makes teams more independent.

Architecture for Multiple Teams

Imagine four teams:

Team A → Accounts

Team B → Payments

Team C → Cards

Team D → Investments

A feature-based architecture allows each team to work within its domain.

Accounts Team
     ↓
features/accounts

Payments Team
     ↓
features/payments

Cards Team
     ↓
features/cards

This reduces conflicts and improves ownership.

When the Application Becomes Very Large

Eventually, even a well-structured monolithic React application can become difficult to manage.

At that point, organizations may consider:

Modular Monolith
        ↓
Micro Frontends

Micro Frontends allow independently developed frontend modules to be composed into a larger application.

For example:

Shell Application
       │
       ├── Accounts
       ├── Payments
       ├── Cards
       └── Investments

However:

Micro Frontends should solve an organizational or deployment problem—not simply be introduced because the application is large.

Architecture Decision Framework

Before introducing a new technology, ask:

What problem are we solving?
        ↓
How frequently does this problem occur?
        ↓
How many teams are affected?
        ↓
What complexity does the solution introduce?
        ↓
Is the benefit greater than the cost?

This is architectural thinking.

Example Enterprise Architecture

A mature React application might look like:

┌──────────────────────────────┐
│          React UI            │
├──────────────────────────────┤
│ Components / Pages / Routes  │
├──────────────────────────────┤
│     Application Services     │
├──────────────────────────────┤
│       Domain Logic           │
├──────────────────────────────┤
│ Infrastructure / API Layer   │
├──────────────────────────────┤
│ REST / GraphQL / External    │
│ Services                     │
└──────────────────────────────┘

This separation makes the application easier to evolve.

Common Architectural Mistakes

1. Overengineering

Don't introduce:

10 Layers
20 Abstractions
5 State Libraries

for a simple application.

Architecture should match the problem.

2. Creating a Global Utility for Everything

A huge utils.ts file eventually becomes difficult to understand.

Group utilities by domain when appropriate.

3. Excessive Shared Code

Sharing code is useful.

But excessive sharing creates coupling.

Sometimes duplication is cheaper than creating a tightly coupled abstraction.

4. Mixing Infrastructure with Business Logic

Avoid:

Component
   ↓
Axios
   ↓
Business Rules

Keep infrastructure replaceable.

Senior Engineer Mindset

A junior developer often asks:

"How can I implement this feature?"

A senior developer asks:

"Where should this feature belong?"

An architect asks:

"How will this decision affect the system six months from now?"

That shift in thinking is extremely important.

Architecture Checklist

Before adding a new feature, ask:

What business domain does it belong to?
What state does it require?
Is that state local or global?
Does it require server data?
Where should API communication live?
Can the logic be reused?
What should be publicly exposed?
How will it be tested?
What happens when the API fails?
Will this architecture scale to additional teams?

Key Takeaways

Today, we learned:

✅ Large React applications need clear architectural boundaries.
✅ Feature-based architecture improves scalability and ownership.
✅ High cohesion and low coupling are fundamental principles.
✅ Clean Architecture separates UI, application, domain, and infrastructure concerns.
✅ Not every piece of state belongs in Redux.
✅ Dependency injection concepts can improve testability even in React.
✅ Micro Frontends should be introduced only when they solve a real organizational or deployment problem.
✅ Good architecture is about managing complexity, not adding complexity.