From Green Screens to React: Modernizing Logistics Terminals Without Downtime

The average enterprise rewrite takes 18 to 24 months, and 70% of these projects either fail or significantly exceed their original timeline. In the logistics sector, where terminals operate 24/7 and "downtime" is measured in millions of dollars per hour, the traditional "Big Bang" rewrite isn't just risky—it’s professional negligence.

TL;DR: Modernizing legacy logistics terminals from green screens to React no longer requires risky manual rewrites; visual reverse engineering allows teams to extract business logic and UI components directly from user workflows, reducing migration timelines by 70%.

The Archaeology Problem: Why Logistics Modernization Stalls#

Most logistics systems are built on decades-old terminal emulators (IBM 3270/5250). These "green screens" are remarkably efficient for power users but represent a massive bottleneck for integration, training, and talent acquisition. The primary hurdle isn't the technology—it's the lost knowledge.

With 67% of legacy systems lacking up-to-date documentation, the first six months of a modernization project are typically spent in "software archaeology." Developers must manually trace COBOL or PL/I logic to understand why a specific field behaves the way it does. This manual extraction averages 40 hours per screen. When you have 500+ screens in a global logistics hub, the math simply doesn't work.

The global technical debt has ballooned to $3.6 trillion because we have treated modernization as a translation exercise rather than an extraction exercise. We try to read the code to understand the business, instead of observing the business to understand the code.

The Visual Reverse Engineering Alternative#

The future of modernization isn't rewriting from scratch; it's understanding what you already have through automated observation. Instead of hiring consultants to interview retired COBOL programmers, Replay allows you to record real user workflows in their native environment.

By treating the video as the source of truth, the platform extracts the underlying state transitions, API requirements, and UI patterns. This shifts the timeline from 18 months of "guessing" to days of "extracting."

Comparison: Modernization Methodologies#

💰 ROI Insight: Manual screen documentation takes ~40 hours per screen. Replay reduces this to ~4 hours by automating the component and contract generation, representing a 90% reduction in labor costs for the discovery phase.

Moving From Green Screens: A Technical Framework#

Modernizing a terminal-based system requires more than just a "skin." You need to preserve the complex business logic—often hidden in "Function Keys" (F1-F12)—while transitioning to a stateless, component-based React architecture.

Step 1: Workflow Recording and State Mapping#

Instead of reading 50,000 lines of legacy code, you record a senior logistics coordinator performing a "Container Intake" workflow. Replay captures the screen transitions, input validations, and the "invisible" logic that occurs between screens.

Step 2: Automated Component Extraction#

The platform identifies recurring UI patterns. In a green screen environment, what looks like a text block is often a complex data grid. Replay generates documented React components that mirror this functionality but utilize a modern Design System.

Step 3: API Contract Generation#

Legacy systems often lack documented APIs. Visual reverse engineering observes the data flow to generate OpenAPI specifications or Zod schemas. This allows your new React frontend to communicate with the legacy backend (via a middleware or mainframe connector) without guessing the data types.

typescript
// Example: Generated React Component from a Replay Extraction
// This component preserves the legacy F-key logic while providing a modern UI

import React, { useEffect } from 'react';
import { useLogisticsStore } from './store';
import { Button, DataGrid, Notification } from '@acme-logistics/design-system';

export const ContainerIntake: React.FC = () => {
  const { containers, fetchContainers, submitIntake } = useLogisticsStore();

  // Replay extracted the F3 (Exit) and F10 (Submit) logic 
  // from the legacy terminal workflow
  useEffect(() => {
    const handleKeyDown = (e: KeyboardEvent) => {
      if (e.key === 'F10') submitIntake();
      if (e.key === 'F3') window.history.back();
    };
    window.addEventListener('keydown', handleKeyDown);
    return () => window.removeEventListener('keydown', handleKeyDown);
  }, [submitIntake]);

  return (
    <div className="p-6">
      <header className="mb-4">
        <h1 className="text-2xl font-bold">Container Intake Portal</h1>
        <p className="text-gray-600">Legacy System ID: TX-990</p>
      </header>
      
      <DataGrid 
        data={containers} 
        columns={[
          { key: 'id', label: 'Container ID' },
          { key: 'origin', label: 'Port of Origin' },
          { key: 'weight', label: 'Weight (kg)' }
        ]}
      />

      <div className="mt-4 flex gap-2">
        <Button onClick={submitIntake} variant="primary">
          Submit (F10)
        </Button>
        <Button variant="secondary">
          Exit (F3)
        </Button>
      </div>
    </div>
  );
};

⚠️ Warning: Never attempt to modernize the UI and the Database simultaneously. This is the #1 cause of project failure. Keep the legacy data source as the "Source of Truth" and use generated API contracts to bridge the gap.

Managing Architectural Drift in Regulated Environments#

For logistics companies operating in government-contracted or highly regulated spaces, compliance is a major hurdle. Manual rewrites often introduce "architectural drift," where the new system subtly changes how business rules are applied, leading to audit failures.

By using Replay's AI Automation Suite, you generate E2E tests based on the original recorded workflows. If the legacy system required three validation steps for hazardous materials, the generated React flow will require those same three steps, verified against the original video recording.

From Black Box to Documented Codebase#

The primary value of Replay isn't just the code—it's the Library. It creates a living repository of your enterprise's architecture.

1. •Flows: Visual maps of how data moves from a terminal to the cloud.
2. •Blueprints: The technical specifications for every screen, including technical debt audits.
3. •Contracts: Auto-generated TypeScript interfaces that ensure the frontend and backend never fall out of sync.

typescript
/**
 * Generated API Contract: ContainerValidation
 * Source: Terminal Workflow "Hazardous_Material_Check"
 * Extraction Date: 2023-10-24
 */

export const ContainerValidationSchema = z.object({
  containerId: z.string().regex(/^[A-Z]{4}\d{7}$/),
  hazardClass: z.number().min(1).max(9),
  weightInKg: z.number().positive(),
  isInternational: z.boolean(),
  portAuthCode: z.string().length(5),
});

export type ContainerValidation = z.infer<typeof ContainerValidationSchema>;

Eliminating the "Documentation Gap"#

The most significant risk in logistics modernization is the "Documentation Gap." When a developer leaves, the knowledge of how the terminal handled "Split Shipments" leaves with them. Replay turns these workflows into permanent assets.

The platform’s ability to function On-Premise is critical for industries like manufacturing and government, where data cannot leave the local network. You record the workflow, the AI processes the video locally, and the React components are generated within your secure environment.

💡 Pro Tip: Use the "Technical Debt Audit" feature in Replay before starting your migration. It will identify which legacy screens are redundant (often up to 30%), allowing you to skip them entirely and save weeks of development time.

Frequently Asked Questions#

How does Replay handle complex business logic hidden in the mainframe?#

Replay uses "Visual Reverse Engineering" to observe the inputs and outputs of the system. By recording multiple variations of a workflow, the AI identifies the conditional logic (e.g., "If Field A is > 100, then Screen B appears"). This allows us to replicate the logic in React without needing to refactor the original COBOL code immediately.

Can we modernize incrementally?#

Yes. This is the recommended approach. Using the Strangler Fig pattern, you can replace one terminal screen at a time with a Replay-generated React component. The two systems can coexist, sharing the same backend, until the legacy interface is fully phased out.

What about SOC2 and HIPAA compliance?#

Replay is built for regulated environments. We offer SOC2 compliance, HIPAA-ready configurations, and full On-Premise deployment options. Your source code and video recordings never have to leave your infrastructure.

Does Replay generate "spaghetti code"?#

No. Replay generates clean, modular React components based on your specific Design System. If you don't have a Design System, Replay’s Library feature helps you build one from the recurring patterns found in your legacy applications.

---

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