The VP of Engineering’s 90-Day Plan for Legacy Decommissioning

The average enterprise rewrite is a career-ending trap. While 70% of legacy rewrites fail or exceed their timelines, the global technical debt bill has ballooned to $3.6 trillion. For the VP of Engineering, the mandate isn't just to "modernize"—it's to stop the bleeding without crashing the business. The traditional "Big Bang" approach, which takes 18–24 months of manual archaeology, is no longer a viable strategy in a market that demands agility.

TL;DR: Successful legacy decommissioning requires shifting from manual code archaeology to visual reverse engineering, reducing the modernization timeline from years to a 90-day execution window.

The Fallacy of the Clean Slate#

Most VPs of Engineering inherit a "black box." It’s a monolith—likely Java Swing, Delphi, or an aging .NET framework—that powers 80% of the company's revenue but has 0% of its original architects remaining. When leadership suggests a "clean slate" rewrite, they are usually signing up for two years of discovery and zero years of delivery.

The problem is documentation. Or rather, the lack of it. Statistics show that 67% of legacy systems lack any meaningful documentation. This forces your most expensive senior engineers to spend months playing "technical archaeologist," digging through layers of spaghetti code to understand business logic that was written in 2004.

At Replay, we’ve seen that the future of modernization isn't rewriting from scratch—it's understanding what you already have by observing it in action.

The 90-Day Modernization Framework#

If you cannot decommission a legacy module in 90 days, you haven't modernized it; you've just started another legacy project. Here is the accelerated roadmap for technical leaders.

Days 1-30: The Technical Debt Audit & Triage#

You cannot fix what you cannot see. The first 30 days are dedicated to mapping the "As-Is" state. Instead of reading code, record the workflows.

1. •Identify High-Value Workflows: Don't try to move the whole monolith. Identify the top 20% of screens that handle 80% of the user traffic.
2. •Record the Truth: Use Replay to record real user interactions within the legacy system. This creates a "Video as a Source of Truth," capturing every state change, API call, and UI transition.
3. •Audit the Gap: Compare the recorded workflows against your desired modern architecture.

💰 ROI Insight: Manual documentation takes an average of 40 hours per screen. With Replay’s visual extraction, that time is reduced to 4 hours. That is a 90% reduction in discovery overhead.

Days 31-60: Extraction and Automated Documentation#

Once the workflows are recorded, the "black box" becomes transparent. This is where you move from observation to extraction.

1. •Generate React Components: Instead of hand-coding new UI, use Replay to extract documented React components directly from the recorded legacy sessions. This ensures the business logic embedded in the UI (form validations, conditional rendering) is preserved.
2. •Define API Contracts: Legacy systems often have undocumented, "accidental" APIs. Replay generates OpenAPI/Swagger specs based on the actual traffic observed during the recording phase.
3. •Establish the Design System: Use the Replay Library to centralize the extracted components into a unified Design System, ensuring consistency across the new modern stack.

typescript
// Example: Generated React component from Replay video extraction
// This component preserves the legacy business logic for a Financial Services portal
import React, { useState, useEffect } from 'react';
import { ModernButton, ModernInput, Alert } from '@enterprise/design-system';

export function LegacyClaimsProcessor({ claimId }: { claimId: string }) {
  const [data, setData] = useState<any>(null);
  const [error, setError] = useState<string | null>(null);

  // Business logic preserved: Legacy systems often had complex 
  // validation rules hidden in the frontend.
  const validateClaim = (values: any) => {
    if (values.amount > 5000 && !values.supervisorOverride) {
      return "Supervisor override required for claims over $5000";
    }
    return null;
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow">
      <h2 className="text-xl font-bold">Claim Processing: {claimId}</h2>
      {/* Modernized UI components mapped to legacy state */}
      <ModernInput 
        label="Claim Amount" 
        value={data?.amount} 
        onChange={(val) => setData({...data, amount: val})}
      />
      {error && <Alert type="error">{error}</Alert>}
      <ModernButton onClick={() => {
        const err = validateClaim(data);
        if (err) setError(err);
        else submitToModernAPI(data);
      }}>
        Process Claim
      </ModernButton>
    </div>
  );
}

Days 61-90: Integration and Decommissioning#

The final phase is the "Bridge." You aren't turning off the legacy system overnight; you are routing traffic to the new, documented components.

1. •E2E Test Generation: Replay automatically generates Playwright or Cypress tests based on the original legacy recordings. This ensures the new system behaves exactly like the old one.
2. •Shadow Deployment: Run the new React-based screens in parallel with the legacy system to verify data integrity.
3. •The Kill Switch: Once parity is confirmed via the generated E2E tests, decommission the legacy module.

⚠️ Warning: Never decommission a legacy module without a generated API contract. If you don't know what the downstream systems are consuming, you will break the enterprise.

Why Technical Leaders are Abandoning Manual Rewrites#

The "Modernize without rewriting" movement is gaining traction in regulated industries—Financial Services, Healthcare, and Government—where the risk of data loss is catastrophic.

The Archaeology Problem#

In a traditional rewrite, your best engineers spend 6 months reading COBOL or old Java code just to write a Jira ticket. This is a waste of human capital. By using Replay, you shift the burden from "reading code" to "observing behavior."

The Documentation Gap#

67% of legacy systems have no documentation. When you use video as the source of truth for reverse engineering, the documentation is a byproduct of the process, not an afterthought. You get:

• •Automated API Contracts
• •Component Documentation
• •Technical Debt Audits
• •Business Logic Flowcharts

💡 Pro Tip: Use the "Flows" feature in Replay to visualize the architecture of your legacy system before you write a single line of new code. Seeing the data flow visually often reveals hidden dependencies that would take weeks to find in the source code.

Case Study: Financial Services Modernization#

A Tier-1 bank had a legacy mortgage processing system with 400+ screens. Their initial estimate for a manual rewrite was 24 months and $12M.

The Replay Approach:

• •Discovery: Recorded 400 workflows in 2 weeks.
• •Extraction: Generated 80% of the React frontend and API contracts using Replay’s AI Automation Suite.
• •Result: The first module was in production in 45 days. The entire system was modernized in 6 months.
• •Total Savings: 70% reduction in time-to-market and 60% reduction in budget.

json
// Generated API Contract from Legacy Traffic
{
  "endpoint": "/api/v1/mortgage/calculate-rate",
  "method": "POST",
  "headers": {
    "Content-Type": "application/json",
    "X-Legacy-Session": "string"
  },
  "requestBody": {
    "creditScore": "integer",
    "loanAmount": "number",
    "downPayment": "number",
    "propertyZip": "string"
  },
  "response": {
    "status": 200,
    "body": {
      "interestRate": "number",
      "monthlyPayment": "number",
      "isApproved": "boolean"
    }
  }
}

Challenges in Regulated Environments#

For VPs in Healthcare (HIPAA) or Finance (SOC2), security is the primary blocker for modernization tools. This is why Replay is built for on-premise deployment. You don't have to send your sensitive legacy data to a third-party cloud. You can run the visual extraction within your own secure perimeter.

• •SOC2 Type II Compliant
• •HIPAA-ready data masking
• •On-Premise / VPC Deployment available

The Future is Understanding, Not Rewriting#

The era of the 2-year rewrite is over. The $3.6 trillion technical debt crisis won't be solved by throwing more developers at manual code reviews. It will be solved by platforms that can "see" legacy systems and translate them into modern codebases automatically.

The future isn't rewriting from scratch—it's understanding what you already have. By adopting a visual reverse engineering strategy, the VP of Engineering can transform from a "maintenance manager" into a "growth accelerator."

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual rewrite takes 18–24 months, Replay typically reduces the timeline by 70%. Most enterprise screens can be documented and converted into React components in under 4 hours, compared to the 40-hour industry average for manual extraction.

What about complex business logic preservation?#

Replay captures the behavior of the system. By recording real user sessions, we capture exactly how the legacy system handles edge cases, validations, and state transitions. This "Visual Source of Truth" ensures that the generated React components and API contracts reflect the actual business logic, even if it's undocumented in the original source code.

Does Replay support green-screen or terminal-based systems?#

Yes. Replay’s visual reverse engineering engine is designed to capture workflows from web-based legacy systems, Citrix-delivered apps, and even terminal emulators. If a user can interact with it on a screen, Replay can document and help modernize it.

How does this fit into a CI/CD pipeline?#

Replay generates E2E tests (Cypress/Playwright) and API contracts that can be immediately integrated into your modern CI/CD pipeline. This ensures that as you decommission legacy modules, your new services are automatically validated against the original system's behavior.

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