Modernizing Air-Gapped Systems: Secure Legacy Extraction for Defense and Infrastructure

The most dangerous systems in the world are the ones we no longer understand. In defense, aerospace, and critical infrastructure, air-gapped systems represent a paradox: they are too critical to fail, yet too opaque to easily modernize. When the original engineers have retired and the documentation has vanished, these "black boxes" become a liability.

The $3.6 trillion global technical debt isn't just a financial figure; it’s a security risk. In regulated environments, the standard "Big Bang" rewrite is a suicide mission. Statistics show that 70% of legacy rewrites fail or significantly exceed their timelines, often stretching from an estimated 18 months to three or four years of development hell. For air-gapped systems, where you cannot simply "cloud migrate" your way out of trouble, the challenge is even steeper.

TL;DR: Modernizing air-gapped systems requires moving away from "manual archaeology" toward Visual Reverse Engineering, allowing teams to extract documented React components and API contracts from legacy UIs in weeks rather than years.

The High Cost of "Manual Archaeology"#

Most legacy systems lack documentation—67%, to be precise. When dealing with air-gapped environments in government or manufacturing, that number often hits 100%. Architects are forced into "software archaeology," manually clicking through screens, sniffing local network traffic, and guessing at business logic buried in 20-year-old COBOL or Java monoliths.

The manual approach is grueling. It takes an average of 40 hours per screen to manually document, design, and write the initial code for a modernized version. In a system with 200 screens, you're looking at 8,000 man-hours just to reach the starting line.

The Modernization Matrix: Air-Gapped Edition#

Why "Rewriting from Scratch" is a Fallacy#

The "rewrite from scratch" mentality assumes that the current system's value is in its code. It isn't. The value is in the business logic—the thousands of edge cases, regulatory requirements, and operational nuances that have been baked into the system over decades.

When you rewrite from scratch, you lose those edge cases. This is why Replay focuses on understanding what you already have. By using video as the source of truth, Replay records real user workflows within the air-gapped environment. It doesn't need to "call home" to a cloud server; it can run entirely on-premise, satisfying SOC2 and HIPAA-ready requirements.

⚠️ Warning: Attempting to modernize without a captured "Source of Truth" for business logic results in "Logic Drift," where the new system fails to handle 20% of critical edge cases, leading to immediate post-launch rollbacks.

Technical Implementation: From Legacy UI to Modern React#

The transition from a legacy Delphi, PowerBuilder, or old Java Swing UI to a modern React architecture typically requires a massive manual lift. Replay's AI Automation Suite accelerates this by extracting the visual and functional intent directly from recorded sessions.

Step 1: Secure Workflow Recording#

In an air-gapped environment, a Replay instance is deployed on-premise. Users perform their standard duties—processing a claim, managing a grid, or authorizing a payload. Replay records the DOM changes (if web-based) or visual state transitions (if desktop-based).

Step 2: Component Extraction#

The system analyzes the recording to identify patterns. It recognizes that a specific pixel cluster is actually a "Data Grid" with sorting and filtering capabilities.

typescript
// Example: Generated React Component from Replay Extraction
// This component preserves the functional logic observed in the legacy system
import React, { useState, useEffect } from 'react';
import { LegacyDataGrid, ModernButton } from '@internal/design-system';

interface MissionData {
  id: string;
  status: 'ACTIVE' | 'PENDING' | 'ARCHIVED';
  payload_kg: number;
}

export const MissionControlPanel: React.FC = () => {
  const [data, setData] = useState<MissionData[]>([]);
  const [isLoading, setIsLoading] = useState(true);

  // Business Logic extracted from legacy workflow: 
  // "System must validate payload weight before enabling launch button"
  const totalWeight = data.reduce((acc, item) => acc + item.payload_kg, 0);
  const isLaunchDisabled = totalWeight > 5000;

  return (
    <div className="p-6 border-red-500 bg-slate-900">
      <h2 className="text-xl font-bold text-white">Extracted Mission Module</h2>
      <LegacyDataGrid 
        dataSource="/api/v1/mission-critical" 
        onDataLoad={(d) => {
          setData(d);
          setIsLoading(false);
        }}
      />
      <div className="mt-4 flex gap-4">
        <ModernButton 
          variant="primary" 
          disabled={isLaunchDisabled || isLoading}
        >
          Execute Sequence
        </ModernButton>
        {isLaunchDisabled && (
          <span className="text-red-400">⚠️ Payload Limit Exceeded</span>
        )}
      </div>
    </div>
  );
}

Step 3: API Contract Generation#

One of the hardest parts of modernizing air-gapped systems is the lack of API documentation. Replay observes the data flowing between the UI and the backend during the recording. It then generates an OpenAPI (Swagger) specification that matches the real-world usage, not just the theoretical design.

yaml
# Generated API Contract from Replay Technical Debt Audit
openapi: 3.0.0
info:
  title: Legacy Infrastructure API
  version: 1.0.0
paths:
  /auth/authorize-sequence:
    post:
      summary: Extracted from "Sequence Authorization" workflow
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                type: object
                properties:
                  auth_token:
                    type: string
                  sequence_id:
                    type: integer

The Architecture of Understanding: Library, Flows, and Blueprints#

To move from an 18-month timeline to a matter of weeks, Enterprise Architects need a structured way to manage the reverse engineering process. Replay provides three core pillars:

1. •Library (Design System): As screens are recorded, Replay identifies recurring UI patterns. It automatically builds a library of React components that mirror your legacy system's functionality but use modern, accessible code.
2. •Flows (Architecture): This maps the "user journey." In complex defense systems, a single task might span 15 screens. Flows visualize this path, identifying bottlenecks and redundant steps that can be optimized during modernization.
3. •Blueprints (Editor): This is where architects refine the extracted code. Instead of writing from scratch, you are editing high-fidelity drafts generated by Replay’s AI.

💰 ROI Insight: Manual modernization costs roughly $15,000 - $25,000 per screen when factoring in developer hours, QA, and project management. Replay reduces this to approximately $2,500 per screen by automating the discovery and boilerplate phases.

Security in Regulated Environments#

For industries like Financial Services and Defense, "Cloud-First" is often "Security-Last." Air-gapped systems exist for a reason. Replay’s architecture respects this by offering:

• •On-Premise Deployment: No data ever leaves your secure perimeter.
• •PII/PHI Masking: Automated redaction of sensitive data during the recording and extraction phase.
• •Audit Trails: Every extraction and generated component is logged, providing a clear chain of custody from the legacy system to the modern codebase.

📝 Note: Replay is built to be HIPAA-ready and supports SOC2 compliance workflows, making it suitable for the most stringent regulatory environments in healthcare and government.

Step-by-Step Guide to Air-Gapped Modernization#

Step 1: Deployment & Discovery#

Deploy Replay on-premise. Identify the core "Power Users" who understand the legacy workflows. These individuals are your primary source of truth.

Step 2: Recording the "Golden Path"#

Record the "Golden Paths"—the most common and critical workflows. For a manufacturing system, this might be "Inventory Reorder" or "Quality Control Logging."

Step 3: Automated Extraction#

Let Replay process the recordings. Within hours, you will have a Technical Debt Audit and a set of "Blueprints." This replaces the "Archaeology" phase that usually takes months.

Step 4: Component Refinement#

Use the generated React components to build your new UI. Because the components are already mapped to the legacy logic, the risk of "Logic Drift" is virtually eliminated.

Step 5: E2E Test Parity#

Replay generates End-to-End (E2E) tests based on the original recordings. You can run these tests against your new system to ensure functional parity. If the old system required three clicks to authorize a shipment, the new system’s test suite ensures the same business outcome is achieved.

Frequently Asked Questions#

How does Replay handle non-web legacy systems (e.g., Mainframe or Desktop)?#

Replay uses advanced computer vision and OCR to interpret desktop applications. While web-based systems allow for deeper DOM inspection, our visual reverse engineering engine can identify buttons, inputs, and data tables in legacy Windows or Linux desktop environments, generating equivalent modern web components.

Does Replay require access to the legacy source code?#

No. Replay is a "Black Box" reverse engineering tool. It works by observing the system's behavior and output. This is critical for systems where the source code is lost, obfuscated, or written in languages that current staff cannot read.

What is the average time savings for an Enterprise project?#

Our partners see an average of 70% time savings. A project that was slated for 18 months of manual discovery and development can typically be completed in 5-6 months, with the initial "documented codebase" ready in just days or weeks.

How do we handle complex business logic that isn't visible on screen?#

While Replay captures all "visible" logic (validations, UI state, navigation), hidden backend logic is captured via API contract extraction. By observing the data payloads sent to the backend, Replay infers the required data structures and logic, providing a blueprint for backend engineers to follow.

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