Cutting Migration Costs: The Financial Difference Between Code-First and Workflow-First Discovery

Legacy modernization is a $3.6 trillion graveyard of "Big Bang" rewrites that failed to cross the finish line. When an enterprise decides to modernize a monolithic system, the first instinct is typically "Code-First Discovery"—assigning a team of architects to perform digital archaeology on a codebase that has lacked documentation for a decade. This approach is the primary reason 70% of legacy rewrites fail or significantly exceed their timelines.

The financial drain isn't just the developers' salaries; it’s the opportunity cost of an 18-to-24-month freeze on new feature development while the team tries to figure out what the old system actually does.

TL;DR: Workflow-first discovery via Visual Reverse Engineering reduces migration costs by 70% by bypassing manual code archaeology and using real user interactions as the source of truth for modern React components.

The Financial Trap of Code-First Discovery#

In a traditional code-first migration, your most expensive assets—Senior Architects—spend 67% of their time reading undocumented code. They are looking for business logic buried in stored procedures, deprecated libraries, and "spaghetti" dependencies.

The math is brutal. For a standard enterprise application with 100 screens:

• •Manual Discovery: 40 hours per screen (Audit + Logic Mapping + UI Spec) = 4,000 hours.
• •At $150/hr: $600,000 just to understand what you have before a single line of new code is written.

By the time the "New System" is ready for UAT, the business requirements have shifted, and the "New" system is already legacy. This is why the average enterprise rewrite timeline stretches to 18 months.

Comparison: Discovery Methodologies#

The Shift to Workflow-First Discovery#

Workflow-first discovery treats the legacy system as a "black box." Instead of reading the code to guess the behavior, we record the behavior to generate the code. This is where Replay changes the financial equation. By recording real user workflows, the platform performs Visual Reverse Engineering to output documented React components and API contracts.

💰 ROI Insight: Companies using Replay see an average time savings of 70%, moving from an 18-month roadmap to a production-ready state in weeks. This effectively reclaims millions in developer hours.

Capturing the "Black Box" Logic#

When you record a workflow in Replay, the platform isn't just taking a video; it’s capturing the DOM state, the network calls, and the state transitions. It then maps these to a modern Design System.

typescript
// Example: Replay-generated API Contract from a Legacy Insurance Portal
// Extracted from a 15-year-old ASP.NET WebForms recording

export interface PolicyClaimWorkflow {
  claimId: string;
  status: 'PENDING' | 'APPROVED' | 'REJECTED';
  adjusterId: number;
  // Logic captured from observed runtime behavior:
  // If claimAmount > 5000, requireSecondaryApproval is triggered
  claimAmount: number;
  requireSecondaryApproval: boolean;
}

/**
 * @generated Generated by Replay AI Automation Suite
 * Source: Workflow "Submit_Property_Claim_V3"
 * Target: Modern React/Node.js Stack
 */
export async function submitClaim(data: PolicyClaimWorkflow) {
  const response = await fetch('/api/v1/claims', {
    method: 'POST',
    body: JSON.stringify(data),
    headers: { 'Content-Type': 'application/json' }
  });
  return response.json();
}

Eliminating the "Documentation Gap"#

67% of legacy systems lack documentation. In a code-first approach, you pay developers to write documentation that will be obsolete by the time the project ends.

Replay’s Flows and Blueprints features create a living map of your architecture. Instead of a static PDF, you have a visual library of every user journey. This is critical for regulated industries like Financial Services and Healthcare, where an audit trail of "How the old system calculated X" is a legal requirement.

⚠️ Warning: Relying on developer memory for legacy logic is the #1 cause of post-migration production bugs. Always use runtime data as the source of truth.

The 4-Step Workflow-First Migration#

To cut migration costs, you must move away from the "Analyze-Everything" phase and toward the "Extract-Functionality" phase.

Step 1: Workflow Assessment#

Identify the critical paths. In a banking app, this might be "International Wire Transfer." Instead of analyzing the entire 1M line codebase, you focus only on the code triggered by that workflow.

Step 2: Visual Recording#

A subject matter expert (SME) performs the task in the legacy environment while Replay records. The platform captures the UI structure and the underlying data flow.

Step 3: Extraction and Generation#

Replay’s AI Automation Suite processes the recording. It identifies UI patterns and maps them to your modern Library (Design System).

tsx
// Example: React component extracted and modernized from a legacy Manufacturing ERP
import { Button, TextField, Card } from "@enterprise/design-system";

export const InventoryUpdateForm = ({ initialData }) => {
  // Replay preserved the validation logic observed during the recording
  const handleValidation = (value: number) => {
    if (value < 0) return "Stock cannot be negative";
    return null;
  };

  return (
    <Card title="Update Warehouse Stock">
      <TextField 
        label="Item SKU" 
        defaultValue={initialData.sku} 
        readOnly 
      />
      <TextField 
        label="Quantity" 
        type="number" 
        onValidate={handleValidation}
      />
      <Button variant="primary" onClick={() => { /* Logic preserved */ }}>
        Sync to Global Ledger
      </Button>
    </Card>
  );
};

Step 4: Technical Debt Audit#

Before deployment, Replay generates a Technical Debt Audit. It compares the extracted modern component against the legacy workflow to ensure 1:1 parity in business logic, ensuring no "logic drift" occurred during the migration.

Implementation Details: Why Visual Reverse Engineering Wins#

The primary cost driver in migration is Uncertainty.

• •Code-First = High Uncertainty (What does this
  text

  if(x && !y)
  block from 2008 do?)
• •Workflow-First = High Certainty (When the user clicks 'Submit', these 3 APIs are called with these parameters.)

By using Replay, you are essentially creating a "Digital Twin" of your legacy system's behavior. This allows for a Strangler Fig migration pattern that actually works. You can replace one workflow at a time, routing traffic from the legacy UI to the new Replay-generated React components without breaking the backend.

📝 Note: For organizations in Government or Telecom, Replay offers an On-Premise deployment. This ensures that sensitive workflow data never leaves your secure network, maintaining HIPAA and SOC2 compliance throughout the migration process.

Real-World Impact: Financial Services Case Study#

A Tier-1 bank attempted to modernize their commercial lending portal using a code-first approach. After 12 months and $4M spent, they had only migrated 15% of the screens. The complexity of the legacy Java applets was too high.

They switched to Replay and adopted a workflow-first strategy:

1. •Recorded 50 core lending workflows in two weeks.
2. •Extracted React components that mapped directly to their new Tailwind-based design system.
3. •Generated E2E tests automatically from the recordings to ensure parity.
4. •Result: The remaining 85% of the application was modernized in 4 months at a fraction of the initial budget.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While manual extraction takes roughly 40 hours per screen, Replay reduces this to approximately 4 hours. Most of this time is spent on SME recording and final architectural review, rather than manual coding.

Does Replay work with legacy technologies like Mainframe or Delphi?#

Yes. Because Replay uses Visual Reverse Engineering, it focuses on the output and the network layer. As long as there is a user interface (Web, Terminal Emulator, or Desktop) and a data exchange, Replay can map the workflow and generate modern documentation and components.

What about business logic preservation?#

Replay captures the "Observed Logic"—the inputs, the outputs, and the state changes. Our AI Automation Suite then suggests the corresponding TypeScript logic. This is then verified against the legacy system using the generated E2E tests to ensure 100% parity.

Is the generated code maintainable?#

Unlike "low-code" platforms that output proprietary junk, Replay generates standard React, TypeScript, and Playwright tests. The code is indistinguishable from code written by a senior developer and follows your organization's specific linting and architectural rules.

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