Supply Chain Resilience: Modernizing AS/400 Systems for Real-Time Logistics

The global supply chain is currently anchored by a $3.6 trillion technical debt. In warehouses and distribution centers worldwide, the core logic for inventory management, order fulfillment, and cross-docking still runs on IBM i (AS/400) systems designed in the 1980s. While these systems are legendary for their "five-nines" reliability, they have become the primary bottleneck for Supply Chain Resilience.

When a logistics provider needs to integrate real-time IoT tracking or AI-driven demand forecasting, they hit the "Green Screen Wall." The logic is trapped in RPG or COBOL, the original architects have retired, and 67% of these systems lack any form of updated documentation. The traditional answer—a "Big Bang" rewrite—is a suicide mission; 70% of legacy rewrites fail or significantly exceed their 18-24 month timelines.

TL;DR: Modernizing AS/400 for real-time logistics no longer requires high-risk manual rewrites; Visual Reverse Engineering extracts legacy workflows into documented React components and API contracts in days, not years.

The Cost of "Documentation Archaeology"#

For most Enterprise Architects, the first step in modernization is "archaeology"—spending months interviewing terminal operators and digging through thousands of lines of undocumented RPG code to understand business rules. This manual process averages 40 hours per screen just to document the requirements.

In a high-velocity supply chain, this delay is terminal. While your team is trying to figure out how the

subroutine handles partial shipments, your competitors are deploying real-time visibility platforms.

Comparing Modernization Strategies#

Beyond Terminal Emulation: Visual Reverse Engineering#

The future of supply chain resilience isn't found in better terminal emulators. It’s found in understanding what you already have. Replay shifts the paradigm from "reading code" to "observing behavior." By recording real user workflows as they navigate the AS/400 green screens, Replay captures the visual state, the data transitions, and the underlying business logic.

This is "Video as a source of truth." Instead of a developer guessing what a function key does, Replay records the transaction, maps the fields, and generates a modern technical stack.

💰 ROI Insight: Manual screen documentation takes ~40 hours per screen. Replay reduces this to 4 hours by automating the extraction of UI logic and API contracts.

Step 1: Workflow Recording#

A subject matter expert (SME) performs a standard logistics task—for example, a "Receive and Putaway" workflow—on the existing legacy terminal. Replay records the session, capturing every field interaction, validation error, and state change.

Step 2: Logic Extraction#

The Replay AI Automation Suite analyzes the recording. It identifies that a specific F3 key press triggers a commit to the DB2 database and maps the screen coordinates to semantic data fields (e.g.,

, , ).

Step 3: Component Generation#

Replay generates a documented React component that mirrors the legacy logic but utilizes a modern design system. It also generates the API contracts required to bridge the new frontend with the legacy backend.

typescript
// Example: Generated React Component for AS/400 Inventory Update
// Extracted via Replay Visual Reverse Engineering

import React, { useState } from 'react';
import { useInventoryAPI } from '@/hooks/useInventoryAPI';
import { Button, Input, Alert } from '@/components/ui';

export const InventoryPutaway: React.FC = () => {
  const [sku, setSku] = useState('');
  const [location, setLocation] = useState('');
  const { updateStock, loading, error } = useInventoryAPI();

  // This logic preserves the legacy "Validation Rule 402" 
  // extracted from the AS/400 workflow recording
  const handlePutaway = async () => {
    if (sku.length === 12 && location.startsWith('WH-')) {
      await updateStock({ sku, location });
    }
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <h2 className="text-xl font-bold mb-4">Real-Time Putaway</h2>
      <Input 
        label="Scan SKU" 
        value={sku} 
        onChange={(e) => setSku(e.target.value)} 
      />
      <Input 
        label="Bin Location" 
        value={location} 
        onChange={(e) => setLocation(e.target.value)} 
      />
      <Button onClick={handlePutaway} disabled={loading}>
        {loading ? 'Updating Legacy System...' : 'Confirm Putaway'}
      </Button>
      {error && <Alert type="error" message={error.message} />}
    </div>
  );
};

Bridging the Gap: API Contract Generation#

The biggest failure point in supply chain modernization is the interface between the new web UI and the legacy RPG programs. Replay solves this by generating precise API contracts based on the observed data flow. This prevents "integration hell" where the frontend expects a JSON object that the backend cannot provide.

⚠️ Warning: Never attempt to modernize a supply chain system without a locked API contract. Mismatched data types between AS/400 (EBCDIC) and modern web services (UTF-8) are a leading cause of data corruption in legacy migrations.

Generated OpenAPI Specification (Snippet)#

Replay produces the following contract from the visual recording, ensuring the mid-tier integration layer knows exactly what the AS/400 expects.

yaml
# Generated by Replay AI Automation Suite
openapi: 3.0.0
info:
  title: Legacy Warehouse Management API
  version: 1.0.0
paths:
  /inventory/update:
    post:
      summary: Extracted from 'Screen_INV_502'
      parameters:
        - name: warehouse_id
          in: header
          required: true
          schema:
            type: string
            pattern: '^[0-9]{3}$'
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                sku: { type: string }
                qty: { type: integer }
                bin: { type: string }

Solving the "Black Box" Problem in Regulated Industries#

For industries like Healthcare logistics or Government manufacturing, "how" a system works is as important as "if" it works. Compliance auditors require documentation that often doesn't exist for 30-year-old systems.

Replay’s Blueprints and Library features provide an instant Technical Debt Audit. By visualizing the flows, architects can see exactly where the legacy system is inefficient.

• •Flows (Architecture): Visualizes how data moves from a green screen terminal through the mid-tier to the database.
• •Library (Design System): Ensures that as you modernize 50 different logistics screens, they all use the same standardized React components, preventing "UI sprawl."
• •SOC2 & HIPAA-ready: Because Replay can be deployed On-Premise, sensitive supply chain data never leaves your secure environment.

📝 Note: Supply chain resilience is not just about uptime; it's about agility. If it takes six months to change a business rule in your AS/400 system, you are not resilient—you are rigid.

The 70% Time Savings: A Case Study in Logistics#

Consider a Tier 1 automotive parts supplier. They had 400+ screens in their AS/400 system managing "Just-in-Time" (JIT) delivery. A manual rewrite was quoted at $12M and 24 months.

Using Replay, they:

1. •Recorded the top 50 high-impact workflows (80% of daily volume).
2. •Extracted the React components and API contracts automatically.
3. •Identified 15 redundant steps in the legacy workflow that were artifacts of 1990s hardware limitations.
4. •Deployed a modern, mobile-responsive warehouse app in 12 weeks.

The result? They moved from an 18-month average enterprise rewrite timeline to a 3-month delivery cycle. They didn't "rewrite" the system; they understood it, extracted it, and evolved it.

Implementation Steps for Enterprise Architects#

Step 1: Identification of Critical Paths#

Don't modernize everything. Identify the workflows that directly impact supply chain resilience—inventory visibility, shipping manifests, and carrier integration.

Step 2: Visual Recording with Replay#

Have your most experienced operators run through these workflows. Replay will capture the "hidden" knowledge—the weird workarounds and specific key combinations—that developers would never find in the source code.

Step 3: Technical Debt Audit#

Use the generated Blueprints to identify bottlenecks. Is the system making 10 database calls for a single SKU lookup? Replay’s audit will highlight these inefficiencies.

Step 4: Incremental Deployment (Strangler Fig 2.0)#

Use the Replay-generated components to build a modern frontend. Route traffic to the new UI while keeping the AS/400 as the system of record. This reduces risk to near-zero.

💡 Pro Tip: Use Replay’s E2E Test generation to ensure that the new modern UI produces the exact same data output as the legacy green screen. This is the ultimate "safety net" for supply chain data integrity.

Frequently Asked Questions#

How does Replay handle complex business logic hidden in RPG?#

Replay observes the outputs of that logic. If entering a specific code on screen A changes the available options on screen B, Replay identifies that state dependency. It extracts the "behavioral contract" of the logic, allowing you to replicate it in a modern service or continue calling the legacy program via a clean, generated API.

Is this just screen scraping?#

No. Traditional screen scraping is brittle and breaks when a pixel moves. Replay performs Visual Reverse Engineering. It understands the underlying DOM (or terminal buffer), the data types, and the workflow state. It generates production-ready React code and TypeScript interfaces, not just a "skin" over a terminal.

Can Replay work with custom or highly modified AS/400 environments?#

Yes. Because Replay is platform-agnostic and records the user's interaction with the interface, it doesn't matter how customized the backend is. If a human can navigate it, Replay can extract it.

What is the typical time-to-value?#

Most enterprise pilots see their first fully documented and functional React component within 48 hours of the first recording. The average time savings for a full project is 70% compared to manual modernization.

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