Breaking the Frontend Monolith: Using Visual Extraction to Seed Your Micro-frontend Architecture

The global economy is currently sitting on $3.6 trillion in technical debt, and the vast majority of that debt is locked inside un-documented frontend monoliths. For the Enterprise Architect, the "Big Bang" rewrite is no longer a viable strategy; it is a career-ending risk. With 70% of legacy rewrites failing or significantly exceeding their timelines, the industry is shifting toward a more surgical approach: Visual Reverse Engineering.

Breaking the frontend monolith isn't just about moving code from one repository to another. It’s about understanding the "black box" of existing user workflows and extracting functional logic without the manual archaeology that consumes 67% of a typical modernization budget.

TL;DR: Modernizing legacy frontend monoliths into Micro-frontend (MFE) architectures fails when teams attempt manual rewrites; Replay uses Visual Reverse Engineering to extract documented React components and API contracts directly from user workflows, reducing migration time by 70%.

The Archaeology Trap: Why Manual Modernization Fails#

Most enterprise systems—especially in Financial Services and Healthcare—suffer from a documentation gap. When 67% of legacy systems lack up-to-date documentation, the first six months of any "Breaking the Frontend" project are usually spent in "archaeology mode." Developers sit with users, record sessions, and try to guess what the underlying logic is by reading 10-year-old jQuery or Angular 1.x code.

The math for manual extraction simply doesn't scale:

• •Manual extraction: 40 hours per screen (discovery, documentation, logic mapping, UI recreation).
• •Replay extraction: 4 hours per screen (automated recording and component generation).

When you are dealing with an enterprise application with 200+ screens, the manual approach represents a 4-year project. By the time you finish, the "modern" stack you chose is already obsolete.

Comparison of Modernization Strategies#

Seeding Your Micro-frontend Architecture#

To successfully break the monolith, you need a "Seed." This is the core set of components, API contracts, and business logic that will populate your new Micro-frontend architecture. Instead of writing these from scratch, Replay allows you to record a real user workflow in your legacy system and automatically generate the React components that mirror that functionality.

The Architecture of a Visual Extraction#

Visual Reverse Engineering works by capturing the DOM mutations, network calls, and state changes during a live user session. It doesn't just "scrape" the UI; it understands the intent.

1. •The Library (Design System): Extracted UI elements are normalized into a modern Design System.
2. •The Flows (Architecture): User journeys are mapped into state machines.
3. •The Blueprints (Editor): Developers refine the generated code before it enters the new MFE shell.

💰 ROI Insight: Companies using Replay see an average of 70% time savings. A project slated for 18 months is frequently delivered in under 3 months by bypassing the discovery phase.

Technical Implementation: From Legacy Flow to React Component#

Let's look at what a generated component looks like when extracted via Replay. Imagine a legacy insurance claims portal. The original code is a tangled mess of global variables and direct DOM manipulation. Replay records the "Submit Claim" workflow and generates a clean, typed React component.

typescript
// Example: Generated component from Replay Visual Extraction
// Source: Legacy Claims Portal (v2.4)
// Target: Modern React / Tailwind MFE

import React, { useState, useEffect } from 'react';
import { Button, Input, Alert } from '@/components/ui'; // From Replay Library
import { useClaimsStore } from './store';

interface ClaimFormProps {
  userId: string;
  onSuccess: (claimId: string) => void;
}

export const ExtractedClaimForm: React.FC<ClaimFormProps> = ({ userId, onSuccess }) => {
  const [isSubmitting, setIsSubmitting] = useState(false);
  const { validateClaim, submitToLegacyAPI } = useClaimsStore();

  // Business logic preserved from legacy system recording
  const handleSubmit = async (event: React.FormEvent<HTMLFormElement>) => {
    event.preventDefault();
    setIsSubmitting(true);
    
    const formData = new FormData(event.currentTarget);
    const payload = Object.fromEntries(formData.entries());

    try {
      // Replay automatically identifies the API contract from network captures
      const response = await submitToLegacyAPI('/api/v1/claims/process', {
        ...payload,
        submitted_by: userId,
        timestamp: new Date().toISOString()
      });
      
      if (response.status === 200) {
        onSuccess(response.data.id);
      }
    } catch (error) {
      console.error("Modernization Error: Logic mismatch in extraction", error);
    } finally {
      setIsSubmitting(false);
    }
  };

  return (
    <form onSubmit={handleSubmit} className="space-y-4 p-6 bg-white rounded-lg shadow">
      <h2 className="text-xl font-bold">Submit New Insurance Claim</h2>
      <Input label="Policy Number" name="policy_no" required />
      <Input label="Incident Date" name="incident_date" type="date" />
      <Button type="submit" loading={isSubmitting}>
        Submit Claim
      </Button>
    </form>
  );
};

💡 Pro Tip: Use the generated API Contracts from Replay to build your Backend-for-Frontend (BFF) layer. This ensures your new Micro-frontend communicates perfectly with the legacy backend from day one.

The 4-Step Workflow to Break the Monolith#

Step 1: Workflow Recording#

Instead of reading code, record the application in action. A business analyst or QA engineer performs the standard tasks—onboarding a client, processing a payment, or generating a report. Replay captures the "Video as a source of truth."

Step 2: Component & Logic Extraction#

The Replay AI Automation Suite analyzes the recording. It identifies repeating UI patterns (buttons, inputs, tables) and groups them into a reusable Library. Simultaneously, it extracts the data fetching logic and state transitions, creating "Flows."

Step 3: Technical Debt Audit#

Before moving code into the new MFE, Replay provides a Technical Debt Audit. This identifies hard-coded values, security vulnerabilities in the legacy API calls, and logic redundancies that should not be carried over to the new architecture.

Step 4: Seeding the MFE Shell#

The extracted components are exported into your new architecture (e.g., a Module Federation setup or a Vercel-hosted MFE). Because the code is already documented and tested (Replay generates E2E tests automatically), the integration phase is shortened by months.

typescript
// Example: Seeding an MFE with extracted logic
// webpack.config.js (Module Federation)

module.exports = {
  name: 'claims_mfe',
  filename: 'remoteEntry.js',
  exposes: {
    './ClaimForm': './src/components/ExtractedClaimForm',
    './ClaimDetails': './src/components/ExtractedClaimDetails',
  },
  shared: {
    react: { singleton: true },
    'react-dom': { singleton: true },
  },
};

⚠️ Warning: Do not attempt to "clean up" legacy logic during the initial extraction. First, achieve functional parity in the new environment, then refactor. Changing business logic and architecture simultaneously is the leading cause of rewrite failure.

Solving the Documentation Gap#

The most significant pain point in enterprise modernization is the "Black Box" problem. When the original developers have left the company and the source code is a spaghetti of undocumented changes, the risk of breaking critical business logic is 100%.

Replay turns the "Black Box" into a "Glass Box." By using video as the source of truth, you aren't relying on what the code says it does; you are relying on what the system actually does in production. This is the difference between "Code Archaeology" and "Visual Reverse Engineering."

• •Documentation without archaeology: Automatically generate Markdown docs for every component.
• •E2E Tests: Replay generates Playwright or Cypress tests based on the recorded user flow.
• •SOC2 & HIPAA Ready: For regulated industries like Telecom and Government, Replay offers On-Premise deployments to ensure data never leaves your secure perimeter.

From 18 Months to 18 Days#

We recently worked with a Tier-1 Financial Services firm that had been trying to migrate their core banking portal for two years. They had managed to migrate only 15% of the UI. By implementing Replay, they were able to:

1. •Record the remaining 85% of workflows in two weeks.
2. •Extract 450+ React components that matched their new design system.
3. •Generate the API contracts for 120 legacy endpoints.
4. •Complete the migration 14 months ahead of their original (stalled) schedule.

📝 Note: Visual extraction isn't just about the UI. It's about preserving the complex validation logic and edge cases that are often buried in legacy frontend code.

Frequently Asked Questions#

How does Replay handle complex business logic buried in the frontend?#

Replay's AI Automation Suite analyzes the state transitions and side effects during a recording. It maps how input values affect the UI and what network requests are triggered. While it generates clean React code, it preserves the logical flow of the original application, ensuring that complex validations aren't lost in translation.

Can we use Replay in a highly regulated, air-gapped environment?#

Yes. Replay is built for Enterprise. We offer On-Premise installations and are SOC2 and HIPAA-ready. Your source code and user recordings never have to leave your infrastructure.

Does Replay work with old frameworks like Silverlight or Flash?#

Replay excels at modernizing any web-based legacy system, including those built on older frameworks like AngularJS (1.x), Backbone.js, or even server-side rendered JSP/ASP.NET pages. If it renders in a browser, Replay can extract it.

What is the average time savings compared to a manual rewrite?#

Our partners report an average of 70% time savings. Specifically, the "Discovery and Documentation" phase—which usually takes 6 months—is reduced to days. The "Development" phase is reduced from 40 hours per screen to approximately 4 hours per screen.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.