Reducing OPEX by 40%: The Impact of Modernizing Legacy UIs on Cloud Infrastructure Costs

Your legacy UI isn't just a technical debt problem; it’s a line item on your P&L that is bleeding 40% more cash than it should. While most CTOs focus on backend refactoring to save on cloud costs, the frontend—often a monolithic "black box" of jQuery, JSP, or Silverlight—remains a massive contributor to operational expenditure (OPEX).

Every hour your team spends on "software archaeology" to fix a bug in a system that lacks documentation is capital that could have been spent on innovation. With global technical debt sitting at $3.6 trillion, the traditional "Big Bang" rewrite is no longer a viable strategy—70% of those projects fail or exceed their 18-24 month timelines. The future of enterprise architecture isn't rewriting from scratch; it’s understanding what you already have through Visual Reverse Engineering.

TL;DR: Reducing OPEX by 40% is achievable by bypassing manual documentation and using Visual Reverse Engineering to extract legacy UI logic into modern, cloud-native React components in days rather than years.

The Hidden OPEX of Legacy UIs#

When we talk about "Reducing OPEX by" significant margins, we have to look beyond just server costs. Legacy systems carry a "hidden tax" that manifests in four specific areas:

1. •Infrastructure Inefficiency: Legacy UIs often require heavy, stateful server-side rendering (SSR) on expensive, over-provisioned VMs. Modern SPAs (Single Page Applications) offload the rendering work to the client's browser and can be hosted on serverless edge networks for pennies.
2. •The Documentation Gap: 67% of legacy systems lack any meaningful documentation. When a change is needed, engineers spend 80% of their time reading code and 20% writing it. This "archaeology" is a massive OPEX drain.
3. •Developer Toil: Senior engineers—your most expensive assets—are often stuck maintaining "spaghetti code" instead of building new features. This leads to burnout and high turnover costs.
4. •Testing Bottlenecks: Manual regression testing for legacy systems is slow and error-prone. Without automated E2E tests, every deployment is a high-risk event that requires "all hands on deck" support.

The Cost of Manual Modernization#

Traditionally, if you wanted to move a screen from a legacy system to React, it took an average of 40 hours per screen. This included discovery, logic mapping, CSS extraction, and state management reconstruction.

Why "Big Bang" Rewrites are OPEX Killers#

The "Big Bang" rewrite is the most common trap in enterprise modernization. It assumes you can freeze feature development for 18 months while you rebuild. In reality, the business continues to evolve, the legacy system continues to accumulate debt, and the "new" system is often obsolete before it even launches.

The primary reason these projects fail is the "Black Box" problem. The original developers are gone, the requirements are lost, and the code itself is the only source of truth—but it's unreadable.

Replay changes this dynamic by using Video as the source of truth. Instead of reading 10,000 lines of undocumented COBOL or old Java, you record a real user workflow. Replay's engine then performs visual reverse engineering to extract the underlying logic, API calls, and UI structure.

💰 ROI Insight: Companies using Replay see a 70% average time saving on modernization projects. What used to take 40 hours of manual labor per screen now takes 4 hours of automated extraction and refinement.

Technical Deep Dive: From Video to React Components#

How does Visual Reverse Engineering actually work? It’s not just a "screenshot to code" tool. It’s a sophisticated capture of the DOM state, network traffic, and business logic triggers.

When you record a workflow in Replay, the platform generates a Blueprint. This blueprint contains the technical DNA of that specific business process.

Step 1: Assessment and Recording#

A business analyst or developer records the legacy application in action. Replay captures every network request, every state change, and every UI transition.

Step 2: Extraction of Logic#

Replay’s AI Automation Suite analyzes the recording. It identifies patterns—for example, a complex validation logic in a legacy form—and converts it into clean, modular React code.

Step 3: Generating API Contracts#

One of the biggest hurdles in "Reducing OPEX by" modernizing is the frontend-backend disconnect. Replay automatically generates API contracts based on the observed traffic during the recording.

typescript
// Example: Generated API Contract from Replay Extraction
// This ensures the new React frontend matches the legacy backend exactly.

export interface LegacyUserPayload {
  userId: string;
  sessionToken: string;
  lastLogin: ISO8601String;
}

export async function fetchLegacyUserData(id: string): Promise<LegacyUserPayload> {
  const response = await fetch(`/api/v1/legacy/profile/${id}`);
  if (!response.ok) throw new Error("Legacy System Timeout");
  return response.json();
}

Step 4: Component Generation#

The output isn't just "div soup." Replay generates documented React components that follow your organization's Design System (via the Replay Library).

tsx
// Example: Migrated Component generated by Replay
import React, { useState, useEffect } from 'react';
import { ModernButton, ModernInput, Alert } from '@enterprise/design-system';

/**
 * @description Extracted from Legacy "Claims Management" Screen - Workflow ID: 882
 * @logic Preserves the original multi-step validation logic from the 2008 JSP implementation.
 */
export const ClaimsFormMigrated = ({ claimId }: { claimId: string }) => {
  const [formData, setFormData] = useState<any>(null);
  const [error, setError] = useState<string | null>(null);

  // Replay identified this specific validation sequence from the legacy trace
  const validateClaim = (data: any) => {
    if (data.amount > 5000 && !data.supervisorCode) {
      return "Supervisory approval required for claims over $5k";
    }
    return null;
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <h2 className="text-xl font-bold mb-4">Process Claim: {claimId}</h2>
      {error && <Alert type="error">{error}</Alert>}
      <form onSubmit={(e) => {
        e.preventDefault();
        const err = validateClaim(formData);
        if (err) setError(err);
        else // Proceed with submission
      }}>
        <ModernInput 
          label="Claim Amount" 
          type="number" 
          onChange={(val) => setFormData({...formData, amount: val})} 
        />
        <ModernButton type="submit">Submit Claim</ModernButton>
      </form>
    </div>
  );
};

Impact on Cloud Infrastructure Costs#

Modernizing the UI layer has a direct, quantifiable impact on your cloud bill.

1. Moving from Stateful to Stateless#

Legacy UIs (like JSF or ASP.NET WebForms) often maintain heavy "ViewState" or session state on the server. This limits your ability to scale horizontally and requires expensive "sticky sessions" on your load balancers. By extracting this logic into a React frontend using Replay, you move the state to the client. This allows you to use cheaper, preemptible instances or serverless functions.

2. Reducing Egress and Compute#

Legacy systems often send massive HTML payloads (the entire page) for every small update. A modernized SPA only sends JSON data. This can reduce network egress costs by up to 60%.

3. Eliminating "Dead Code" Infrastructure#

In a typical enterprise legacy system, 30% of the features are never used. Manual audits to find this "dead code" are expensive. Replay’s Technical Debt Audit feature identifies which screens and components are actually being hit by users, allowing you to decommission unused infrastructure safely.

⚠️ Warning: Modernizing the UI without understanding the underlying API dependencies can lead to "chatter," where the new frontend makes too many small requests, actually increasing latency and cost. Replay mitigates this by generating optimized API contracts that bundle requests where possible.

Implementation Strategy: The 30-Day Modernization Sprint#

If you want to start reducing OPEX by 40%, you don't need a two-year roadmap. You need a 30-day pilot.

1. •Select the "High-Toil" Candidate: Identify a screen or workflow that is either high-traffic or high-maintenance (e.g., a claims processing dashboard or a customer onboarding flow).
2. •Record with Replay: Have a subject matter expert (SME) perform the workflow while Replay records the session.
3. •Extract and Audit: Use the Replay AI Suite to extract the components, API contracts, and E2E tests. Review the Technical Debt Audit to see what can be discarded.
4. •Deploy as a Micro-Frontend: Instead of replacing the whole app, deploy the new React component alongside the legacy app using a proxy or a micro-frontend architecture.
5. •Measure and Scale: Compare the infrastructure costs and developer hours spent on the new screen vs. the legacy version.

📝 Note: Replay is built for regulated environments. Whether you are in Financial Services or Healthcare, Replay offers SOC2 compliance, HIPAA-ready data handling, and On-Premise deployment options to ensure your proprietary logic never leaves your network.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual rewrite of a complex enterprise screen takes roughly 40 hours, Replay reduces this to approximately 4 hours. Most organizations can move from a "black box" legacy system to a fully documented, modern React codebase in 2 to 8 weeks, depending on the number of screens.

What about business logic preservation?#

This is Replay's core strength. Because we use visual reverse engineering based on actual execution traces (recordings), we capture the logic as it actually runs, not as it was supposed to be written in the documentation 15 years ago. The generated code preserves validation rules, conditional rendering, and data transformation logic.

Does Replay work with mainframe-backed web apps?#

Yes. As long as the legacy system is accessible via a browser (even via a terminal emulator or an old IE-only web portal), Replay can record the interactions and extract the UI logic. We've helped companies modernize systems built on everything from PowerBuilder to Silverlight.

How does this impact my existing CI/CD pipeline?#

Replay integrates with your existing workflows. It generates standard React components, TypeScript interfaces, and Playwright/Cypress E2E tests that fit directly into your Git-based development lifecycle.

---

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