From AS/400 to React: A Non-Disruptive Path for Supply Chain Modernization

The average supply chain executive is one retired COBOL programmer away from a catastrophic logistics halt. While the world moves toward real-time visibility and AI-driven forecasting, the backbone of global trade remains locked inside "black box" AS/400 systems that haven't been documented since the late 1990s.

The $3.6 trillion global technical debt isn't just a balance sheet liability; it is an operational wall. When you attempt to move from AS/400 to a modern React-based architecture, you aren't just changing code—you are attempting to perform open-heart surgery on a patient who is currently running a marathon. Traditional "Big Bang" rewrites fail 70% of the time because they rely on "software archaeology"—the manual, error-prone process of trying to guess business logic from undocumented green screens.

TL;DR: Modernizing supply chain systems from AS/400 to React no longer requires high-risk, multi-year rewrites; Replay uses Visual Reverse Engineering to extract business logic and UI components from user workflows, reducing modernization timelines by 70%.

The High Cost of Manual Archaeology#

In the enterprise, the standard approach to modernization is a three-headed monster: manual documentation, requirement gathering through interviews, and a ground-up rewrite. This process typically takes 18 to 24 months for a single core module.

Statistics show that 67% of legacy systems lack any form of up-to-date documentation. In a supply chain context—where edge cases for customs, tariffs, and multi-modal routing are baked into the legacy code—losing that "tribal knowledge" during a rewrite is fatal.

The bottleneck is almost always the "discovery" phase. Manually mapping a single complex AS/400 screen into a modern functional requirement document takes an average of 40 hours. With Replay, that same screen is captured, analyzed, and converted into a documented React component in 4 hours.

Why Supply Chains Get Stuck on the Green Screen#

Supply chain management (SCM) systems on AS/400 are remarkably stable, which is their greatest curse. Because they "just work," they are ignored until the cost of maintenance exceeds the cost of replacement, or until the user experience becomes a hiring liability.

1. •The Documentation Gap: Most AS/400 systems have undergone decades of "hotfixes" that were never documented.
2. •The Talent Gap: Finding developers who understand both RPG/ILE and modern Next.js/React patterns is nearly impossible.
3. •The Integration Gap: Modern APIs don't talk to legacy DB2 databases without expensive, brittle middleware.

⚠️ Warning: Attempting to rewrite your supply chain logic based solely on "user interviews" will miss approximately 30% of critical edge cases that are handled implicitly by the legacy system.

The Replay Methodology: Visual Reverse Engineering#

The future of modernization isn't rewriting from scratch; it’s understanding what you already have through Visual Reverse Engineering. Instead of reading millions of lines of RPG code, Replay records real user workflows. By observing how a logistics coordinator processes a Bill of Lading, Replay identifies the data inputs, the state changes, and the business logic required to replicate that functionality in React.

Step 1: Workflow Recording and Discovery#

Instead of manual audits, teams use Replay to record actual production workflows. This creates a "Video as Source of Truth." Every keystroke and screen transition on the AS/400 terminal is captured. Replay’s AI Automation Suite then parses these recordings to identify repetitive UI patterns and underlying data structures.

Step 2: Extracting the Component Library#

Replay takes the visual data and generates a standardized Design System. In a supply chain context, this means your "Inventory Grid" or "Shipping Manifest" becomes a reusable React component.

typescript
// Example: Generated React component from AS/400 "Order Entry" workflow
// Extracted via Replay Blueprints

import React, { useState, useEffect } from 'react';
import { LegacyDataConnector } from '@replay-internal/core';

interface OrderEntryProps {
  terminalId: string;
  initialWarehouseCode: string;
}

export const OrderEntryModule: React.FC<OrderEntryProps> = ({ terminalId, initialWarehouseCode }) => {
  const [sku, setSku] = useState('');
  const [quantity, setQuantity] = useState(0);
  const [validationError, setValidationError] = useState<string | null>(null);

  // Business logic preserved from legacy AS/400 screen behavior
  const handleValidation = (value: string) => {
    if (value.length > 15) {
      setValidationError("SKU exceeds legacy DB2 field limit (15 chars)");
    } else {
      setValidationError(null);
    }
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <h2 className="text-xl font-bold mb-4">Modernized Order Entry</h2>
      <div className="space-y-4">
        <input 
          value={sku} 
          onChange={(e) => { setSku(e.target.value); handleValidation(e.target.value); }}
          placeholder="Enter SKU"
          className="border p-2 w-full"
        />
        {validationError && <p className="text-red-500 text-sm">{validationError}</p>}
        
        <input 
          type="number" 
          value={quantity} 
          onChange={(e) => setQuantity(Number(e.target.value))}
          className="border p-2 w-full"
        />
        
        <button 
          onClick={() => console.log("Submitting to Legacy Bridge...")}
          className="bg-blue-600 text-white px-4 py-2 rounded"
        >
          Update Inventory
        </button>
      </div>
    </div>
  );
};

Step 3: Generating API Contracts and Documentation#

The biggest risk in moving from AS/400 to modern web frameworks is the data layer. Replay automatically generates API contracts (OpenAPI/Swagger) based on the observed data flow between the user and the legacy backend.

yaml
# Generated API Contract for AS/400 Inventory Update
openapi: 3.0.0
info:
  title: Supply Chain Legacy Bridge
  version: 1.0.0
paths:
  /inventory/update:
    post:
      summary: Extracted from AS/400 Screen ID: INV004
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                warehouse_id: {type: string, maxLength: 4}
                item_number: {type: string, maxLength: 15}
                adjustment_qty: {type: integer}
      responses:
        '200':
          description: Success

💡 Pro Tip: Use the generated API contracts to build a "Strangler Fig" facade. This allows you to swap out the AS/400 backend for a modern cloud database later without changing the React frontend.

Step 4: Technical Debt Audit and E2E Testing#

Before deployment, Replay’s AI Suite performs a Technical Debt Audit. It identifies which parts of the legacy workflow are redundant. In many supply chain systems, 20% of the screens are no longer used but still maintained. Replay flags these for decommissioning, saving immediate maintenance costs.

💰 ROI Insight: Companies using Replay see an average 70% reduction in modernization time. For a typical $2M modernization project, this translates to $1.4M in saved engineering hours and a 12-month faster time-to-market.

Case Study: Manufacturing Logistics Modernization#

A global manufacturing firm needed to move their parts-tracking system from AS/400 to a modern React application to support mobile tablets on the factory floor.

• •Manual Estimate: 14 months, 6 developers, $1.2M cost.
• •Replay Reality: 3 months, 2 developers, $350k cost.

By recording the workers using the green screens, Replay identified that 40% of the manual data entry was actually redundant and could be automated via API calls. The resulting React app wasn't just a "skin" of the old system; it was a streamlined version that increased worker productivity by 22%.

Built for Regulated Environments#

Supply chain systems often fall under strict regulatory oversight, especially in Healthcare (HIPAA) or Government contracting. Replay is built for these environments:

• •SOC2 Type II Compliant
• •HIPAA-ready data masking during recording
• •On-Premise Deployment available for air-gapped systems

You don't have to send your sensitive logistics data to the cloud to modernize it. Replay can run entirely within your secure perimeter.

Frequently Asked Questions#

How long does the extraction process take for a typical AS/400 module?#

While a manual rewrite takes 18-24 months for an enterprise suite, Replay typically extracts and documents a core module in 2 to 8 weeks. Simple screens can be converted into React components in a matter of hours.

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

No. Replay uses Visual Reverse Engineering. It analyzes the "black box" by observing user workflows, inputs, and outputs. This is ideal for systems where the original source code is lost, undocumented, or written in obsolete versions of RPG.

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

Replay maps the "Flows" (Architecture). By observing how different inputs lead to specific screen results or error messages, the AI Automation Suite infers the business rules. These are then documented as functional requirements and E2E tests, ensuring the new React system behaves exactly like the legacy system where it matters most.

What about data migration?#

Replay generates the API contracts necessary for your modern frontend to communicate with legacy databases (DB2, etc.) via a bridge. This allows you to modernize the UI/UX first (the most immediate pain point) while planning a phased data migration later.

Can we customize the generated React code?#

Absolutely. Replay provides "Blueprints" (an Editor) that allow your senior architects to define the coding standards, component libraries (like Tailwind or MUI), and state management patterns (Redux, Zustand) that the generated code must follow.

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