Why Your Cloud Migration Is Stalling at the Application Layer

The "Lift and Shift" era of cloud migration is over, and it has left a trail of expensive, half-finished projects in its wake. Most enterprises successfully moved their VMs to AWS or Azure years ago, only to realize they didn't actually migrate their business—they just moved their technical debt to a more expensive zip code.

The reason why your cloud migration is stalling isn't a lack of Kubernetes expertise or Terraform scripts. It’s the application layer. Specifically, it’s the millions of lines of undocumented, "black box" legacy code that no one on your current team fully understands. When you try to refactor these systems for the cloud, you aren't engineering; you're performing archaeology.

TL;DR: Cloud migrations stall at the application layer because manual reverse engineering of legacy logic is too slow and risky; Replay solves this by using visual recording to automate the extraction of documented React components and API contracts, reducing modernization time by 70%.

The Application Layer Bottleneck#

Infrastructure is now a solved problem. We can spin up a global, multi-region cluster in minutes. But the logic living inside your legacy Java, .NET, or Mainframe-backed web apps remains a mystery.

Statistics show that 67% of legacy systems lack any meaningful documentation. When a VP of Engineering mandates a "Cloud Native" rewrite, the team spends the first six months just trying to map out existing user workflows. This manual "archaeology" is why the average enterprise rewrite timeline is 18 months, and why 70% of legacy rewrites fail or exceed their original timeline.

We are currently facing a $3.6 trillion global technical debt crisis. You cannot solve a trillion-dollar problem with manual documentation and "Big Bang" rewrites.

The Modernization Matrix#

Why Your Cloud Strategy is Failing the "Logic Test"#

Most cloud strategies focus on the where (Cloud vs. On-prem) rather than the what (the business logic). When you attempt to modernize a legacy screen—say, a complex insurance claims portal or a financial trading dashboard—you encounter three primary blockers:

1. •Lost Context: The original developers left five years ago. The "source of truth" is the running application, not the code.
2. •Logic Entanglement: Business rules are buried in UI event handlers, making it impossible to separate the frontend from the backend without breaking things.
3. •Manual Toil: It takes an average of 40 hours to manually document and recreate a single complex legacy screen. With Replay, that time is slashed to 4 hours.

⚠️ Warning: Attempting to rewrite a legacy system without a "Video Source of Truth" leads to "Feature Parity Drift," where the new system misses critical edge cases that were handled by the old code.

Visual Reverse Engineering: The Replay Paradigm#

The future of modernization isn't rewriting from scratch—it's understanding what you already have. At Replay, we’ve pioneered Visual Reverse Engineering.

Instead of reading through 50,000 lines of spaghetti code, you simply record a real user performing a workflow. Replay captures the DOM state, the network calls, and the underlying logic to generate documented, modern React components and API contracts.

How it Works: From Black Box to React#

When you record a session in Replay, the platform doesn't just record a video; it records the state. It then uses an AI Automation Suite to map that state to a modern tech stack.

typescript
// Example: Legacy logic extracted and cleaned by Replay
// Original: Obfuscated jQuery/ASP.NET event handler
// Generated: Clean, documented React component with TypeScript

import React, { useState, useEffect } from 'react';
import { Button, TextField, Alert } from '@/components/ui';

interface ClaimData {
  id: string;
  status: 'PENDING' | 'APPROVED' | 'REJECTED';
  amount: number;
}

/**
 * @component LegacyClaimProcessor
 * @description Extracted from 'ClaimsPortal_v2_final' via Replay.
 * Preserves the complex validation logic for regional tax codes.
 */
export const LegacyClaimProcessor: React.FC<{ claimId: string }> = ({ claimId }) => {
  const [data, setData] = useState<ClaimData | null>(null);
  const [loading, setLoading] = useState(true);

  // Replay extracted this specific API contract from recorded network traffic
  const handleValidation = async (amount: number) => {
    // Logic preserved from legacy 'ValidateTax_Global' function
    if (amount > 10000) {
      return await api.checkCompliance(claimId);
    }
    return true;
  };

  return (
    <div className="p-6 border rounded-lg shadow-sm">
      <h2 className="text-xl font-bold">Process Claim: {claimId}</h2>
      {/* UI components mapped to your internal Design System Library */}
      <TextField 
        label="Adjustment Amount" 
        onChange={(e) => handleValidation(Number(e.target.value))} 
      />
      <Button onClick={() => console.log("Submit")}>Approve</Button>
    </div>
  );
};

The 4-Step Accelerated Migration Workflow#

To get your cloud migration back on track, you need a repeatable factory for application extraction. Here is how enterprise architects are using Replay to move from 18-month timelines to 18-day sprints.

Step 1: Visual Assessment & Recording#

Instead of a "Discovery Phase" that lasts months, you perform a "Recording Phase." Product owners or subject matter experts (SMEs) run through the "Happy Path" and "Edge Case" workflows of the legacy application. Replay captures everything.

Step 2: Component Extraction (The Library)#

Replay’s Library feature identifies recurring UI patterns across your legacy estate. It maps these to your modern Design System. If your legacy app uses 50 different versions of a "Submit" button, Replay consolidates them into a single, standardized React component.

Step 3: Blueprinting & Logic Mapping#

Using the Blueprints (Editor), architects can see the "Flows" of the application. Replay generates:

• •API Contracts: Swagger/OpenAPI specs based on observed traffic.
• •E2E Tests: Playwright or Cypress scripts that replicate the recorded user session.
• •Technical Debt Audit: Identification of dead code paths that were never triggered during the recording.

Step 4: Automated Documentation#

Replay generates the documentation that your team never had time to write. This includes state diagrams, data flow maps, and component hierarchies.

💰 ROI Insight: One Tier-1 Financial Services firm reduced their migration budget from $12M to $3.5M by using Replay to extract 400+ screens from a legacy banking core, avoiding a complete manual rewrite.

Preserving Business Logic in Regulated Environments#

For industries like Healthcare, Insurance, and Government, "losing" logic isn't just a bug—it's a compliance failure. This is why your cloud migration needs a higher level of fidelity than manual coding can provide.

Replay is built for these high-stakes environments:

• •SOC2 & HIPAA Ready: Data masking ensures PII is never captured during the recording process.
• •On-Premise Available: For air-gapped systems or sensitive government workloads, Replay can run entirely within your firewall.
• •Audit Trails: Every extracted component is linked back to the original video recording, providing a clear "Source of Truth" for auditors.

📝 Note: Replay doesn't just generate code; it generates provable code. You can compare the legacy screen side-by-side with the modern React output to ensure 1:1 visual and functional parity.

Bridging the Gap: API Contracts and E2E Tests#

The most dangerous part of an application migration is the "Integration Gap"—where the new frontend fails to talk to the old backend (or vice versa). Replay mitigates this by generating precise API contracts from the legacy system's actual behavior.

json
// Generated API Contract from Replay extraction
{
  "endpoint": "/api/v1/legacy/calculate-premium",
  "method": "POST",
  "observed_payload": {
    "userId": "string",
    "risk_score": "float",
    "is_renewal": "boolean"
  },
  "validation_rules": {
    "risk_score": "Must be between 0 and 1.0",
    "legacy_header": "X-ARCH-TIMESTAMP required"
  },
  "generated_test_path": "tests/e2e/premium_calc.spec.ts"
}

By generating these contracts and E2E tests automatically, Replay ensures that the "Strangler Fig" pattern can be implemented safely. You can swap out legacy modules one by one, confident that the new cloud-native microservice matches the legacy behavior exactly.

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. For a typical 100-screen application, this moves the timeline from a year of development to less than a month.

Does Replay work with "Black Box" systems where we don't have the source code?#

Yes. Because Replay uses Visual Reverse Engineering (recording the DOM and network layer), it does not require access to the original backend source code to document the frontend behavior and API requirements.

What about business logic preservation?#

Replay captures the effects of business logic. While it cannot "see" code running on a COBOL mainframe, it captures the inputs, outputs, and UI changes resulting from that logic. This allows developers to wrap that logic in modern APIs or rewrite it with a clear specification of what the output must be.

Is the generated code maintainable?#

Unlike "low-code" platforms that output "spaghetti" or proprietary formats, Replay generates standard React/TypeScript code that follows your team's specific coding standards and design system. It is meant to be owned and maintained by your developers.

Which industries benefit most from Replay?#

Replay is specifically designed for complex, data-heavy industries including Financial Services (trading platforms, core banking), Healthcare (EHR systems, claims processing), and Manufacturing (ERP/MES interfaces).

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

The $3.6 trillion technical debt problem won't be solved by hiring more developers to write more code. It will be solved by using AI and visual tools to understand the logic we’ve already built.

Stop letting your cloud migration stall at the application layer. Stop guessing what your legacy code does. Start recording, start understanding, and start modernizing.

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