Modernizing Legacy Logistics: Converting AS/400 Terminal Screens to React Workflows

Your logistics operation is likely running on a system designed before the internet was commercialized. While the AS/400 (IBM i) remains a workhorse for global supply chains due to its reliability, it has become a "black box" that stifles innovation. The tribal knowledge required to maintain these green screens is retiring, and the documentation—if it ever existed—is long gone.

The traditional response is a "Big Bang" rewrite. However, data shows that 70% of legacy rewrites fail or significantly exceed their timelines, often stretching into 24-month marathons that drain capital without delivering value. In the high-stakes world of logistics, where downtime costs thousands per minute, you cannot afford a two-year "rip and replace" project.

TL;DR: Modernizing legacy logistics systems no longer requires a high-risk 24-month rewrite; Visual Reverse Engineering allows teams to extract React components and business logic directly from AS/400 workflows in weeks, reducing modernization time by 70%.

The Logistics Technical Debt Trap#

The global technical debt burden has reached $3.6 trillion, and the logistics sector carries a disproportionate share. Most Tier 1 logistics providers still rely on 5250 terminal emulators for core functions: warehouse management (WMS), inventory tracking, and customs clearance.

The problem isn't the stability of the AS/400; it's the documentation gap. Statistics show that 67% of legacy systems lack up-to-date documentation. When you ask a developer to modernize a terminal screen, they spend 90% of their time performing "software archaeology"—manually tracing RPG or COBOL programs to understand hidden business rules.

The Manual Modernization Tax#

Manual reverse engineering is a massive resource sink. On average, it takes 40 hours per screen to manually document, design, and code a modern equivalent of a legacy terminal interface. For a logistics suite with 200+ screens, that’s 8,000 man-hours before you even begin integration testing.

Why "Big Bang" Rewrites Fail in Logistics#

Logistics workflows are uniquely complex. A single "Shipment Entry" screen might trigger a dozen background processes: EDI 214 status updates, tax calculations, carrier rate shopping, and inventory allocation.

When you rewrite from scratch, you inevitably miss the "edge cases" that have been baked into the legacy code over 30 years. These aren't bugs; they are the business rules that handle your most profitable (and complex) customers. Replay solves this by using Video as the Source of Truth. By recording a real user performing a workflow, Replay captures every field interaction, every hidden validation, and every navigational jump.

⚠️ Warning: Attempting to modernize by simply reading legacy RPG/COBOL source code often misses logic triggered by specific data states. Visual reverse engineering captures the actual system behavior, not just the intended code path.

The Replay Methodology: From Green Screen to React in Days#

Replay moves the modernization needle by automating the extraction process. Instead of writing code from a blank slate, you use the AI Automation Suite to generate functional React components based on recorded 5250 terminal sessions.

Step 1: Recording the Workflow#

A subject matter expert (SME) performs a standard task—such as "Process Bill of Lading"—while Replay records the session. This isn't just a screen recording; Replay captures the underlying data structures and state changes.

Step 2: Extraction and Mapping#

The Replay Flows (Architecture) engine analyzes the recording. It identifies input fields, command key triggers (F3 to exit, F12 to cancel), and sub-file grids (the AS/400 version of a table).

Step 3: Component Generation#

Replay’s Blueprints (Editor) generates a modern React component. This isn't "spaghetti code." It produces clean, documented TypeScript that adheres to your organization's design system.

typescript
// Example: Generated React component from an AS/400 Inventory Lookup
import React, { useState, useEffect } from 'react';
import { TextField, DataGrid, Button } from '@your-org/design-system';

interface InventoryItem {
  partNumber: string;
  warehouseLocation: string;
  quantityOnHand: number;
  status: 'Available' | 'Reserved' | 'Damaged';
}

export const InventoryLookup: React.FC = () => {
  const [sku, setSku] = useState('');
  const [results, setResults] = useState<InventoryItem[]>([]);

  // Logic extracted from 5250 Terminal Screen 'INV001R'
  const handleSearch = async () => {
    // Replay generated API contract mapping to legacy backend
    const data = await fetch(`/api/legacy/inventory?sku=${sku}`);
    const json = await data.json();
    setResults(json);
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <h2 className="text-xl font-bold mb-4">WMS Inventory Search</h2>
      <div className="flex gap-4 mb-6">
        <TextField 
          label="Part Number / SKU" 
          value={sku} 
          onChange={(e) => setSku(e.target.value)} 
        />
        <Button onClick={handleSearch} variant="primary">Execute Query</Button>
      </div>
      <DataGrid columns={['SKU', 'Location', 'Qty', 'Status']} rows={results} />
    </div>
  );
};

💰 ROI Insight: By automating the UI and API contract generation, Replay users report an average 70% time savings. A project that would have taken 18 months is reduced to less than 6 months, allowing the business to realize the benefits of modernization a full year earlier.

Preserving Business Logic: The API Contract Problem#

The biggest hurdle in logistics modernization isn't the UI; it's the integration. Your React frontend needs to talk to a backend that expects fixed-width strings or EBCDIC-encoded data.

Replay automatically generates API Contracts. It maps the React form fields back to the specific memory addresses or buffer positions required by the legacy system. This allows you to adopt a Strangler Fig pattern—modernizing the frontend immediately while keeping the stable AS/400 core running until you are ready to migrate the database.

Technical Debt Audit#

Before you write a single line of code, Replay provides a Technical Debt Audit. It scans your recorded workflows to identify:

• •Redundant screens (often 30% of a legacy app)
• •Circular navigation paths
• •Fields that are captured but never used by the backend

💡 Pro Tip: Use the Replay Library (Design System) feature to ensure that every extracted screen automatically uses your company's modern UI components. This ensures visual consistency across the entire enterprise suite.

Security and Compliance in Regulated Logistics#

For companies in healthcare logistics (HIPAA) or government contracting, "cloud-only" tools are a non-starter. Replay is built for high-compliance environments.

• •On-Premise Availability: Keep your proprietary logic and data within your own firewall.
• •SOC2 Type II & HIPAA Ready: Replay meets the rigorous standards required for handling sensitive supply chain data.
• •Air-Gapped Deployment: For manufacturing or government facilities where external internet access is restricted.

Modernizing Without the "Black Box" Risk#

The future of enterprise architecture isn't about throwing away everything you've built. It's about understanding what you already have. Replay turns the "black box" of the AS/400 into a documented, visual codebase.

By using Replay, you are not just building a new UI; you are creating a living documentation of your business. If a senior developer leaves, the "Flows" and "Blueprints" remain, providing a clear map of how the system operates.

Comparison of Modernization Approaches#

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual screen rewrite takes roughly 40 hours, Replay reduces this to approximately 4 hours. For a standard logistics module (20-30 screens), you can have a functional React prototype and documented API contracts in 2-3 weeks.

Does Replay require access to our AS/400 source code?#

No. Replay performs Visual Reverse Engineering. It analyzes the system's behavior and data flow during active sessions. While source code can be helpful for supplementary context, it is not required to generate modern components and documentation.

What about business logic preservation?#

This is Replay’s core strength. By recording real user workflows, we capture the "hidden" logic that occurs between screen transitions. Replay generates E2E tests and documentation that ensure the modern React workflow matches the legacy system's behavior bit-for-bit.

Can we export the code, or are we locked into Replay?#

Replay generates standard, high-quality React and TypeScript. There is no proprietary runtime required. Once the components are generated, they belong to you and can be maintained in your standard CI/CD pipeline.

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