Why Traditional 'Lift and Shift' Fails the Frontend Experience

The $3.6 trillion global technical debt isn't just a backend problem; it’s a UI graveyard. Most enterprise modernization efforts fail not because the database migration went wrong, but because the frontend is a "black box" of undocumented business logic, tribal knowledge, and deprecated frameworks. When leadership mandates a "Lift and Shift" for these legacy systems, they are essentially moving a burning building to a more expensive piece of land.

Traditional "Lift and Shift" fails the frontend experience because it prioritizes infrastructure over intent. It ignores the reality that 67% of legacy systems lack any meaningful documentation, leaving developers to perform "software archaeology" on 15-year-old jQuery or AngularJS codebases. The result? A 70% failure rate for legacy rewrites and timelines that balloon from 6 months to 24 months.

TL;DR: Traditional "Lift and Shift" and "Big Bang" rewrites fail because they attempt to move or recreate implementation details rather than extracting the core business intent, a problem solved by Replay’s Visual Reverse Engineering which cuts modernization time by 70%.

The High Cost of Manual UI Archaeology#

In a typical Financial Services or Healthcare enterprise, a single legacy screen contains hundreds of hidden validation rules, conditional formatting triggers, and state transitions that exist nowhere but the source code. Manually documenting these for a rewrite takes an average of 40 hours per screen. For an application with 50+ screens, you’ve spent a year just on discovery before a single line of React is written.

The "Black Box" Problem#

Legacy frontends often act as the de facto documentation for the business. When you "Lift and Shift," you are either:

1. •Containerizing the Mess: Running the old, insecure code in a new environment, solving none of the technical debt or user experience issues.
2. •Blind Re-implementation: Asking developers to guess how the old system worked by looking at the UI, leading to "parity gaps" where critical business logic is missed.

💰 ROI Insight: Manual reverse engineering costs roughly $150-$200/hour in senior engineering time. Replay reduces the time per screen from 40 hours to 4 hours, representing a 90% cost reduction in the discovery phase.

Comparing Modernization Strategies#

To understand why traditional methods fail, we must look at the data. Most Enterprise Architects are forced to choose between the high risk of a "Big Bang" rewrite and the agonizingly slow "Strangler Fig" pattern.

Why "Lift and Shift" Fails the Frontend#

1. The Logic Leakage#

In legacy systems, business logic is often tightly coupled with the DOM. A "Lift and Shift" approach usually involves wrapping the old UI in a modern shell. However, this creates "Logic Leakage," where the new system must constantly communicate with the old, brittle state management of the legacy app. This increases latency and makes end-to-end testing nearly impossible.

2. The Documentation Gap#

If 67% of your system is undocumented, a "Lift and Shift" is a gamble. You are moving code that no one on your current team fully understands. When the system eventually breaks in the new cloud environment, the "Shift" part of the strategy becomes a liability because the original context is lost.

3. CSS and Global Scope Pollution#

Legacy applications (especially those built in the IE6-IE11 era) rely heavily on global CSS and window-scoped variables. Moving these into a modern micro-frontend architecture without isolation leads to "Style Bleed," where the legacy UI breaks the modern components surrounding it.

⚠️ Warning: Attempting to "Lift and Shift" legacy frontend code into a modern CI/CD pipeline often fails because the legacy code lacks the unit tests and modularity required for automated deployment.

The Alternative: Visual Reverse Engineering with Replay#

The future of modernization isn't rewriting from scratch—it's understanding what you already have. Replay changes the paradigm by using the video of a user workflow as the "Source of Truth." Instead of reading thousands of lines of spaghetti code, Replay records the execution and extracts the intent.

From Video to Documented Codebase#

Replay's engine analyzes the execution path of a user's session to generate clean, modular React components and API contracts. This isn't just a "copy-paste" of the old code; it's a synthesis of the UI's behavior into modern standards.

typescript
// Example: Replay-generated React component from a legacy JSP recording
// Original logic: Hidden in 500 lines of jQuery validation
// Extracted logic: Clean, functional React with TypeScript

import React, { useState } from 'react';
import { useLegacyValidation } from './hooks/useLegacyValidation';

interface ClaimFormProps {
  initialData?: any;
  onSuccess: (data: any) => void;
}

export const InsuranceClaimForm: React.FC<ClaimFormProps> = ({ initialData, onSuccess }) => {
  const [formData, setFormData] = useState(initialData);
  const { validate, errors } = useLegacyValidation(); // Logic preserved from recording

  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault();
    const isValid = await validate(formData);
    if (isValid) {
      // Replay inferred this API contract from the network trace
      const response = await fetch('/api/v1/claims/submit', {
        method: 'POST',
        body: JSON.stringify(formData),
      });
      if (response.ok) onSuccess(await response.json());
    }
  };

  return (
    <form onSubmit={handleSubmit} className="modern-design-system-provider">
      <input 
        type="text" 
        value={formData.policyNumber} 
        onChange={(e) => setFormData({...formData, policyNumber: e.target.value})}
        aria-invalid={!!errors.policyNumber}
      />
      {errors.policyNumber && <span>{errors.policyNumber}</span>}
      <button type="submit">Submit Claim</button>
    </form>
  );
};

The Replay Modernization Workflow#

Modernizing a legacy system with Replay follows a structured, three-step process that eliminates the "Archaeology" phase entirely.

Step 1: Record the Workflow#

A subject matter expert (SME) or QA engineer simply uses the legacy application as they normally would. Replay records the DOM mutations, network requests, and state changes. This captures the "as-is" state of the application, including all those "hidden" business rules that aren't in the documentation.

Step 2: Visual Extraction#

Replay’s AI Automation Suite processes the recording. It identifies repeating patterns to build a Library (Design System) and maps the user journey into Flows (Architecture). It identifies every API call made during the session and generates a Swagger/OpenAPI contract automatically.

Step 3: Blueprint Generation#

The Blueprints (Editor) allow architects to refine the extracted components. You aren't starting with a blank IDE; you're starting with a 70% complete React codebase that matches the functional requirements of the legacy system.

💡 Pro Tip: Use Replay to generate your E2E tests simultaneously. Since Replay knows the exact user path, it can output Playwright or Cypress tests that ensure your new React frontend behaves exactly like the legacy system.

Preserving Business Logic in Regulated Industries#

For Financial Services and Healthcare, "Lift and Shift" is often rejected because of compliance risks. If a rewrite misses a single regulatory validation step, the company faces massive fines.

Replay is built for these environments. With SOC2 and HIPAA-ready compliance and On-Premise availability, Replay ensures that the "Reverse Engineering" happens within your security perimeter. Because the extraction is based on actual user workflows, the resulting "Technical Debt Audit" provides a clear audit trail of what was moved and why.

Automatic API Contract Inference#

One of the biggest pain points in modernization is the lack of backend documentation. Replay monitors the network layer during the recording to generate precise API contracts.

json
// Replay Generated API Contract (OpenAPI 3.0)
{
  "path": "/api/legacy/get-coverage",
  "method": "POST",
  "parameters": [
    { "name": "policy_id", "in": "body", "required": true, "type": "string" }
  ],
  "response_schema": {
    "type": "object",
    "properties": {
      "status": { "type": "string" },
      "coverage_amount": { "type": "number" },
      "last_updated": { "type": "string", "format": "date-time" }
    }
  }
}

Addressing the "Why Not Just Rewrite?" Argument#

VPs of Engineering often argue that a "fresh start" is better for morale and code quality. While true in a vacuum, the reality of the enterprise is different.

1. •The Knowledge Vacuum: The people who wrote the original system are gone. A rewrite is a game of telephone where information is lost at every step.
2. •The Opportunity Cost: Every month spent on a legacy rewrite is a month your competitors are shipping new features. Replay moves you from "Modernizing" to "Innovating" in weeks, not years.
3. •The Testing Burden: In a traditional rewrite, you have to write tests for the new system and the old system to ensure parity. Replay generates these tests for you based on the recording.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual rewrite of a complex module takes 18-24 months, Replay typically completes the extraction and documentation phase in 2 to 8 weeks, depending on the number of unique workflows.

What about business logic preservation?#

Replay captures the intent of the logic by observing state changes and network calls. It doesn't just copy the code; it documents the behavior so your developers can implement it using modern, clean patterns in React.

Does Replay work with mainframe-backed web apps?#

Yes. As long as the legacy system is accessible via a browser (e.g., terminal emulators, JSP, Silverlight, ASP.NET, PowerBuilder web), Replay can record the session and extract the frontend components and API interactions.

Can we run Replay on-premise?#

Absolutely. We understand that Financial Services and Government sectors cannot send sensitive data to the cloud. Replay offers a fully containerized on-premise solution that keeps all recordings and generated code within your infrastructure.

The Future of the Enterprise Architect#

The role of the Enterprise Architect is shifting from "Project Manager of Failed Rewrites" to "Curator of Automated Insights." By leveraging Visual Reverse Engineering, you stop being the bottleneck and start being the accelerator.

Stop "Lifting and Shifting" your technical debt. Start understanding it. The future isn't rewriting from scratch—it's using Replay to bridge the gap between where you are and where you need to be.

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