# How Instagram, WhatsApp, Uber & Netflix Would Be Built Today Using Expo Router

Most of the react native tutorials teaches you how to build application or new screens but very few talks about the systems.

That is why the developers can easily build attractive screens but failed to manage the architecture when the application scales.

Making a small app is easy but a production scale application is completely different engineering challenge.

The architecture with:

*   5 screens
    
*   1 developer
    
*   3 - 4 API calls
    

will be completely get collapsed when application become:

*   Hundred of screens
    
*   Millions of users
    
*   Multiple team members
    
*   Realtime systems
    
*   Offline support
    
*   Complex navigations
    
*   Background synchronisation
    

That's why the big companies like Instagram, Whatsapp, User ... invest heavy in architecture engineering.

The UI is just a surface for interaction. The actual complexity in underneath.

Let's explore more about how modern large applications are structured, and how the architecture matters in React Native.

## Why Simple folder structure fails to scale

Most beginner react native start like this:

```javascript
/components
/screens
/navigation
/hooks
/utils
/services
```

At first, this structure feels organized but then the app grows. Suddenly:

*   `/components` has 400 files
    
*   `/screens` becomes impossible to navigate
    
*   Logic might be duplicate
    
*   API calls logic are not organized
    
*   Navigation becomes tangled
    

This happens because the structure is organized for small projects, not scalable systems.

Example:

```javascript
/components
    Button.tsx
    MessageBubble.tsx
    FeedCard.tsx
```

These files belong to completely different domains:

*   Button - Shared UI systems
    
*   MessageBubble - Messaging
    
*   FeedCard - Ratings
    

As application scale, this creates:

*   Tight coupling
    
*   Dependency confusion
    
*   Hard to refactor
    

Now, you can see that the architecture has become more important than UI.

## Architecture Thinking vs Small-App Thinking

Small app development focuses on:

**How do I make this screen work?**

Production engineering focuses on:

**How will this system survive growth?**

This difference actual change everything. Production engineering focuses on:

*   Maintainability
    
*   Scalability
    
*   Developer experience
    
*   Performance
    
*   Reliability
    
*   Long-term evolution
    
*   Team collaboration
    
*   Feature isolation
    

At scale, architecture becomes a business decision.

Because poor architecture eventually slows down the entire company.

## The Evolution of Mobile App Architecture

Most apps evolve through stages:

### Beginner Architecture

```plaintext
/components
/screens
/navigation
```

Works fine for:

*   Personal projects
    
*   MVP's
    
*   Small demos
    

But fails for:

*   Multiple developers can join
    
*   The feature will become interconnected
    
*   Business logic grows
    

### Medium Scale Architecture

Developer starts separating:

```plaintext
/api
/store
/hooks
/navigation
/modules
```

This improves the organization of code.

But eventually:

*   Features still depend on each other heavily
    
*   Shared state becomes more complex
    
*   Growing navigation is difficult to manage.
    

### Production Features Architecture

Large applications usually shift towards feature-based architecture.

Instead of organizing by file type:

```plaintext
/components
/hooks/services
```

Example:

```plaintext
/features
    /auth
    /feed
    /chat
    /profile
    /payments
```

This is one of the biggest architectural transitions in large scale enginerring.