Post-Mortem of a $100M Failed Rewrite: Why Logic Discovery is the Single Point of Failure

A $100 million write-off is the price of hubris. It is the cost of believing that your engineering team can "simply rebuild" what took twenty years to create, without first understanding the undocumented edge cases that actually run the business. When a Tier-1 financial institution or a global healthcare provider scraps a multi-year modernization effort, the autopsy rarely points to poor coding standards or the wrong choice of cloud provider. It points to a single, catastrophic failure: Logic Discovery.

TL;DR: Legacy modernization fails when teams prioritize "writing new code" over "extracting existing truth," but Visual Reverse Engineering with Replay reduces discovery time by 90%, turning black-box systems into documented React codebases in weeks rather than years.

The Anatomy of a $100M Grave#

The "Big Bang" rewrite is the most expensive gamble in the enterprise. You start with a $20M budget and an 18-month timeline. Fast forward 36 months: you’ve spent $100M, the legacy system is still the "source of truth," and the new system can't handle 30% of the production edge cases because nobody knew those edge cases existed.

The $3.6 trillion global technical debt isn't just "old code." It’s undiscovered logic. 67% of legacy systems lack any form of accurate documentation. When you attempt to modernize these systems through manual "archaeology"—interviews with retiring subject matter experts and reading millions of lines of COBOL or jQuery—you are essentially trying to reconstruct a dinosaur from a single tooth.

Why Logic Discovery is the Single Point of Failure#

In most enterprise environments, the "system" is actually a collection of tribal knowledge, undocumented API side effects, and "temporary" fixes that have lived in production for a decade.

1. •The Documentation Gap: Manual discovery takes an average of 40 hours per screen. In a 500-screen application, that’s 20,000 man-hours just to understand what to build.
2. •The "Lost" Edge Case: 70% of legacy rewrites fail because the new system breaks a critical, undocumented business rule that only triggers on the third Tuesday of a leap year.
3. •The Talent Drain: The architects who built the original system are gone. The new engineers don't want to read legacy code; they want to write new code. This disconnect is where the $100M disappears.

The Archaeology Problem: Why Manual Extraction is Dead#

Traditional modernization relies on "manual extraction." You hire a consultancy, they spend six months "gathering requirements," and they hand you a 400-page PDF that is obsolete the moment it's saved. This is archaeology, not engineering.

⚠️ Warning: If your modernization strategy starts with "reading the source code to understand the requirements," you have already lost. The code tells you how it works, but the user workflow tells you what it must do.

Manual extraction is the bottleneck. If it takes 40 hours to document a single complex insurance claims screen, and Replay can do it in 4 hours using Visual Reverse Engineering, the math for the "Big Bang" rewrite no longer makes sense. We are seeing a fundamental shift from "Writing from Scratch" to "Understanding and Porting."

Visual Reverse Engineering: The Replay Methodology#

Replay fundamentally changes the "Discovery" phase by using video as the source of truth. Instead of reading code, we record real user workflows. Replay’s AI Automation Suite then analyzes the execution trace, the DOM changes, and the network calls to generate a documented React component and its corresponding API contract.

Step 1: Workflow Recording#

Instead of interviewing a claims adjuster for three hours, you record them performing a "Standard Claim Process" in the legacy system. Replay captures every state change, every hidden validation, and every API call.

Step 2: Automated Extraction#

Replay’s engine parses the recording. It identifies patterns—form fields, data tables, navigation logic—and maps them to your modern Design System (the Replay Library).

Step 3: Blueprint Generation#

The system generates Blueprints. These aren't just "screenshots." They are functional, interactive representations of the legacy logic, complete with technical debt audits and E2E test suites.

Step 4: Code Generation#

Replay outputs clean, production-ready React components. It doesn't just copy the old code; it translates the intent of the legacy system into modern architecture.

typescript
// Example: Replay-Generated Component
// Logic extracted from Legacy Insurance Portal (v4.2)
// Workflow: 'Submit Policy Endorsement'

import React, { useState, useEffect } from 'react';
import { Button, TextField, Alert } from '@/components/ui'; // From Replay Library
import { useEndorsementLogic } from './hooks/useEndorsementLogic';

export const PolicyEndorsementForm = ({ policyId }: { policyId: string }) => {
  // Replay identified this hidden validation logic from the legacy network trace
  const [isQualified, setIsQualified] = useState<boolean>(false);
  const { submit, loading, error } = useEndorsementLogic();

  // Preserved Business Logic: Legacy systems required a 'pre-flight' 
  // check against the underwriting API before enabling the submit button.
  const handlePreFlightCheck = async (data: any) => {
    const response = await fetch(`/api/legacy/underwriting/check?id=${policyId}`);
    const result = await response.json();
    setIsQualified(result.status === 'APPROVED');
  };

  return (
    <div className="p-6 space-y-4">
      <h2 className="text-xl font-bold">Policy Endorsement</h2>
      <TextField 
        label="Endorsement Reason" 
        onChange={(e) => handlePreFlightCheck(e.target.value)} 
      />
      
      {isQualified ? (
        <Button onClick={submit} loading={loading}>
          Submit Endorsement
        </Button>
      ) : (
        <Alert variant="warning">
          This policy requires manual underwriting review.
        </Alert>
      )}
    </div>
  );
};

💰 ROI Insight: By automating the generation of the UI layer and the API contracts, Replay customers report an average of 70% time savings. Projects that were slated for 18 months are being delivered in 12 weeks.

From Black Box to Documented Codebase#

The goal of Replay isn't just to give you new code. It's to give you understanding. Most legacy systems are "Black Boxes"—data goes in, magic happens, and data comes out. When you use Replay, you are creating a "Glass Box."

The AI Automation Suite#

Replay’s AI doesn't just guess. It correlates the visual changes on the screen with the underlying network traffic. If a user clicks "Calculate Interest" and the legacy system hits three different SOAP services, Replay documents that sequence.

Generated API Contracts#

One of the biggest hurdles in modernization is the "Middle Tier." Replay automatically generates OpenAPI/Swagger specifications based on the observed traffic during the recording.

yaml
# Generated by Replay AI - Legacy API Contract
openapi: 3.0.0
info:
  title: Legacy Claims API
  version: 1.0.0
paths:
  /claims/calculate-liability:
    post:
      summary: Extracted from 'High Value Claim' workflow
      parameters:
        - name: claim_id
          in: query
          required: true
          schema:
            type: string
      responses:
        '200':
          description: Preserved logic for liability weighting
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/LiabilityResult'

Security and Compliance in Regulated Environments#

We work with Financial Services, Healthcare, and Government agencies. We know that "cloud-only" is often a non-starter.

• •SOC2 & HIPAA Ready: Replay is built with the highest security standards in mind.
• •On-Premise Availability: For highly sensitive environments (Manufacturing, Defense), Replay can be deployed entirely within your firewall.
• •PII Masking: Our recording engine automatically masks sensitive user data during the extraction process, ensuring that no PII/PHI ever leaves your secure environment.

💡 Pro Tip: Use Replay’s Technical Debt Audit feature early in the project. It identifies which parts of the legacy system are actually used by users and which parts are "dead code" that shouldn't be migrated.

The Future Isn't Rewriting—It's Understanding#

The "Modernize or Die" ultimatum has led to too many $100M failures. The future of enterprise architecture isn't about hiring 500 developers to rewrite a system from scratch. It’s about using Visual Reverse Engineering to understand the value you already have and move it into the future.

Stop treating your legacy system like a liability and start treating it like a blueprint. With Replay, you aren't just guessing what the code does—you're recording the truth and generating the future.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual audit takes 40 hours per screen, Replay reduces this to approximately 4 hours. For a standard enterprise application with 100 screens, you can move from "Black Box" to a fully documented React architecture in 4-6 weeks.

What about business logic preservation?#

Replay doesn't just copy the UI. It captures the interaction between the UI and the backend. By recording real workflows, we capture the "hidden" logic—the validations, the conditional rendering, and the API sequences—that are often missed in manual requirements gathering.

Does Replay work with mainframe or terminal-based systems?#

Yes. If it can be rendered in a browser or through a terminal emulator that Replay can hook into, we can extract the workflow. We specialize in taking "green screen" logic and turning it into modern, accessible React components.

How does this integrate with our existing CI/CD?#

Replay generates standard React code, TypeScript definitions, and E2E tests (Playwright/Cypress). This output can be pushed directly to your Git repository and integrated into your existing deployment pipelines.

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