React Native Migration Strategies: Greenfield, Brownfield & More (Part 4)

Part 4 of an 8-part series on React Native for enterprise. Start with Part 1.

Migration is where theory meets reality. Here are the practical patterns for transitioning existing applications to React Native.

The Migration Decision Tree

Before choosing a strategy, answer:

1. What's the current state?

• Pure native (separate iOS/Android codebases)?
• Single platform only?
• Existing RN app needing modernization?
• Web app expanding to mobile?

2. What's the business driver?

• Development speed?
• Cost reduction?
• Technical debt?
• Platform expansion?

3. What's the risk tolerance?

• Can you tolerate a feature freeze?
• Is phased rollout acceptable?
• How critical is the app to revenue?

Strategy 1: Greenfield Rebuild

What it is: Build new RN app from scratch, retire native apps.

When to use:

• Legacy codebase is unmaintainable
• Tech debt exceeds rebuild cost
• Major feature overhaul planned
• Team lacks native expertise

Phases:

Phase 1: Foundation (4-8 weeks)
├── RN project setup + architecture
├── Core navigation + state management
├── Component library
└── Auth + core APIs

Phase 2: Feature Parity (8-16 weeks)
├── Rebuild features by priority
├── Start with highest-traffic flows
├── Test against native baseline
└── Internal dogfooding

Phase 3: Transition (2-4 weeks)
├── Beta to user subset
├── Monitor crashes + performance
├── Gradual rollout (10% → 50% → 100%)
└── Deprecate native apps

Risks: Extended timeline, feature drift, user disruption

Mitigations: Feature freeze on legacy, parallel testing, rollback plan

Best for: Apps with significant tech debt, products undergoing redesign

Strategy 2: Brownfield Integration

What it is: Add RN to existing native app, migrate features incrementally.

When to use:

• App too critical for rewrite risk
• Some native features work well
• Team has mixed expertise
• Need to prove RN value first

Phases:

Phase 1: Integration (2-4 weeks)
├── Add RN as dependency
├── Set up bridge communication
├── Create container view for RN
└── Navigation handoff patterns

Phase 2: First Feature (2-4 weeks)
├── Choose non-critical, self-contained feature
├── Rebuild in RN
├── Integrate into native nav
└── Validate UX + performance

Phase 3: Expansion (ongoing)
├── Migrate features based on results
├── Native shell becomes thinner
└── Eventually: mostly RN with native edges

Integration pattern (iOS):

class ReactNativeViewController: UIViewController {
    var reactRootView: RCTRootView!

    override func viewDidLoad() {
        super.viewDidLoad()
        reactRootView = RCTRootView(
            bridge: bridge,
            moduleName: "FeatureModule",
            initialProperties: ["userId": user.id]
        )
        view.addSubview(reactRootView)
    }
}

Risks: Larger bundle, complex navigation, UX inconsistency

Best for: Risk-averse orgs, apps with critical native features

Strategy 3: Platform Expansion

What it is: Use RN to add iOS or Android while keeping existing native app.

When to use:

• Single-platform app expanding
• Time-to-market critical
• Can't hire native devs for second platform
• Features are API-driven (good RN fit)

Phases:

Phase 1: Bootstrap (4-6 weeks)
├── Set up RN project
├── Core features matching existing app
├── Use existing APIs
└── Test on new platform

Phase 2: Feature Catch-up (8-12 weeks)
├── Build remaining features
├── Feature parity with native
├── Platform-specific adjustments
└── Beta testing

Phase 3: Maintenance (ongoing)
├── New features in RN first
├── Consider migrating native to RN
└── Or maintain both

Risks: Feature divergence, different bug classes, maintenance overhead

Best for: Single-platform apps needing rapid expansion

Strategy 4: RN Modernization

What it is: Upgrading older RN app to modern architecture.

When to use:

• Old RN (pre-Fabric architecture)
• Outdated dependencies
• Performance problems
• Accumulated tech debt

Phases:

Phase 1: Assessment (1-2 weeks)
├── Audit RN version + dependencies
├── Identify deprecated patterns
├── Measure performance baseline
└── Create upgrade roadmap

Phase 2: Foundation (2-4 weeks)
├── Upgrade RN (incrementally!)
├── Migrate to New Architecture
├── Update navigation
└── Address breaking changes

Phase 3: Modernization (4-8 weeks)
├── Modern state management
├── Replace deprecated libs
├── Add TypeScript
└── Comprehensive testing

Phase 4: Optimization (2-4 weeks)
├── Performance profiling
├── Bundle size optimization
├── Memory leak fixes

New Architecture migration:

// Old (Bridge): Async, serialized
const { MyModule } = NativeModules;
MyModule.doSomething(callback);

// New (TurboModule): Synchronous, direct
import { TurboModuleRegistry } from 'react-native';
const MyModule = TurboModuleRegistry.get('MyModule');
MyModule.doSomething(); // Direct call

Best for: Apps 2+ years old, performance-sensitive applications

Strategy Comparison

Key Takeaways

1. Match strategy to risk tolerance — Greenfield is faster but riskier
2. Brownfield proves value incrementally — Lower risk, longer timeline
3. Don't skip RN versions — Upgrade incrementally
4. Feature freeze during transition — Prevents drift
5. Test obsessively — Migration bugs are hard to catch

Coming in Part 5

Next: Common mistakes that cost companies millions — anti-patterns to avoid in React Native development.

Lotus Innovations specializes in React Native migrations and modernization.

Planning a migration? Let's talk →