From AS/400 to Modern Web: Modernizing Logistics and Supply Chain Interfaces

The green screen is a tombstone for enterprise agility. In the logistics and supply chain sector, the IBM i (AS/400) remains a powerhouse of reliability, yet it acts as a functional "black box" that stifles modern integration. When a warehouse manager has to navigate twenty-five "F-key" commands just to check inventory levels, the system isn't just old—it’s a liability.

The standard industry response is the "Big Bang" rewrite. It is a strategy that fails 70% of the time. You spend 18 to 24 months attempting to document systems where the original authors retired a decade ago, only to realize the business logic has evolved into a spaghetti-mess of RPG and CL (Control Language) that no one dares touch.

TL;DR: Modernizing AS/400 logistics interfaces doesn't require a multi-year RPG-to-Java rewrite; Visual Reverse Engineering with Replay extracts business logic from user workflows directly into documented React components in days, not years.

The High Cost of "Archaeological" Modernization#

Most enterprise architects approach AS/400 modernization like an archaeological dig. They spend months interviewing legacy users and digging through 67% of systems that lack any meaningful documentation. This "manual archaeology" is the primary driver behind the $3.6 trillion global technical debt.

In logistics, where margins are razor-thin, a 24-month rewrite timeline is an eternity. By the time the new system is ready, the market has already shifted toward AI-driven routing and real-time IoT tracking—features the new "modern" system wasn't even designed to handle because the team was too busy translating legacy code.

Why Logistics Rewrites Fail#

The complexity of a Warehouse Management System (WMS) or Transportation Management System (TMS) on an AS/400 isn't just in the code; it’s in the workflow. These systems often contain thirty years of "undocumented features"—specific key combinations that trigger customs filings or carrier-specific manifest rules.

When you attempt to rewrite these from scratch, you miss the nuances. Manual documentation of a single complex logistics screen takes an average of 40 hours. With Replay, that same screen is captured, analyzed, and converted into a functional React component in 4 hours.

⚠️ Warning: Attempting to modernize by simply reading RPG source code often misses critical business logic hidden in the "hidden fields" and display files (*DSPF) of the AS/400 environment.

The Replay Methodology: Video as the Source of Truth#

Instead of digging through source code, Replay uses Visual Reverse Engineering. By recording a real user performing a standard workflow—such as "Receiving a Purchase Order" or "Allocating Carrier Loads"—Replay analyzes the UI transitions, data inputs, and state changes.

Step 1: Workflow Recording#

The subject matter expert (SME) records their screen while performing the task in the legacy terminal emulator. Replay captures every keystroke, screen refresh, and data field.

Step 2: Component Extraction#

Replay’s AI Automation Suite identifies UI patterns (grids, input fields, command prompts) and maps them to a modern Design System. It doesn't just "scrape" the screen; it understands the intent.

Step 3: Logic Mapping & API Generation#

Replay identifies the underlying data structures. If a user enters a SKU and the screen populates weight and dimensions, Replay identifies that functional dependency and generates an API contract.

typescript
// Example: Generated React Component from an AS/400 "Inventory Inquiry" Screen
// Extracted via Replay Visual Reverse Engineering

import React, { useState, useEffect } from 'react';
import { Table, Input, Badge, Card } from '@/components/ui-library'; 

interface InventoryItem {
  sku: string;
  binLocation: string;
  onHand: number;
  allocated: number;
  status: 'Available' | 'Reserved' | 'Damaged';
}

export const WarehouseInquiry: React.FC = () => {
  const [query, setQuery] = useState('');
  const [data, setData] = useState<InventoryItem[]>([]);

  // The logic below was extracted from the legacy 'F4' lookup behavior
  const handleSearch = async (val: string) => {
    const results = await api.fetchLegacyData('/api/v1/inventory', {
      params: { 
        WHLOC: '01', // Preserved legacy warehouse code
        SKU_SEARCH: val 
      }
    });
    setData(results);
  };

  return (
    <Card title="Warehouse Inventory Search">
      <Input 
        placeholder="Scan or Enter SKU..." 
        onChange={(e) => handleSearch(e.target.value)}
      />
      <Table data={data} columns={[
        { header: 'SKU', accessor: 'sku' },
        { header: 'Location', accessor: 'binLocation' },
        { header: 'On Hand', accessor: 'onHand' },
        { 
          header: 'Status', 
          render: (row) => <Badge variant={row.status === 'Available' ? 'success' : 'warn'}>{row.status}</Badge>
        }
      ]} />
    </Card>
  );
};

Bridging the Gap: API Contracts and E2E Tests#

One of the greatest risks in AS/400 modernization is breaking the existing integration points. Logistics systems are often connected via EDI (Electronic Data Interchange) or flat-file transfers.

Replay doesn't just give you a pretty frontend. It generates the technical scaffolding required to make the modernization stick:

• •API Contracts: Automatically generated Swagger/OpenAPI specs based on the data observed during the recording.
• •E2E Tests: Replay generates Playwright or Cypress tests that mirror the legacy workflow, ensuring the new React interface produces the exact same state changes as the green screen.
• •Technical Debt Audit: A comprehensive report of which legacy paths were exercised and which remain "dark code."

💰 ROI Insight: Organizations using Replay see an average of 70% time savings. For a standard logistics suite with 200 screens, this moves the timeline from 18 months down to approximately 12 weeks.

Implementation Roadmap: From AS/400 to Web#

Step 1: Assessment and Recording#

Identify the high-value, high-friction workflows. In logistics, this is usually the "Dock-to-Stock" flow or "Exception Handling" in shipping. Have your best operators record these flows using the Replay recorder.

Step 2: Library Alignment#

Map the extracted elements to your corporate Design System. If you don't have one, Replay’s Library feature generates a consistent set of React components based on your first few extractions.

Step 3: Blueprinting the Architecture#

Use the Blueprints editor to define how the new modern frontend will communicate with the legacy backend. This often involves a "Sidecar" API that sits next to the AS/400, translating REST calls into program calls (via IBM i Access or similar middleware).

yaml
# Generated API Contract for Carrier Assignment
openapi: 3.0.0
info:
  title: Legacy TMS Bridge
  version: 1.0.0
paths:
  /assign-carrier:
    post:
      summary: Extracted from AS/400 Screen TMS002
      parameters:
        - name: orderId
          in: query
          required: true
          schema:
            type: string
      responses:
        '200':
          description: Carrier assigned successfully

Step 4: Validation and Deployment#

Run the generated E2E tests against both the legacy system and the new React interface. When the outputs match 100%, you are ready for a phased rollout.

Built for Regulated Environments#

Modernizing supply chain systems for Government or Healthcare logistics requires strict adherence to security protocols. Replay is built for these environments:

• •SOC2 & HIPAA Ready: Data privacy is baked into the extraction process.
• •On-Premise Availability: Keep your proprietary business logic and recordings within your own firewall.
• •Audit Trails: Every generated component is linked back to the original video recording, providing a clear "source of truth" for auditors.

💡 Pro Tip: Don't try to modernize everything at once. Use Replay to extract the "Outer Loop" of your application (the UI/UX) while keeping the "Inner Loop" (the battle-tested RPG calculations) intact until you are ready for a full database migration.

Frequently Asked Questions#

How does Replay handle complex RPG business logic?#

Replay focuses on the observable behavior of the system. By recording the inputs and the resulting screen changes, it "black-boxes" the RPG logic. It identifies that "Input A + Input B" results in "Output C," allowing you to generate a modern interface that calls the existing legacy logic via an API bridge, or providing the blueprint for a developer to rewrite that specific logic in a modern language.

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

No. Replay works through Visual Reverse Engineering. While having source code is helpful for deep backend migration, Replay can document and extract the entire frontend and workflow logic simply by "watching" the system in use. This is critical for systems where documentation is missing (67% of legacy systems).

What is the learning curve for my team?#

Replay is designed for Enterprise Architects and Frontend Engineers. If your team knows React and can navigate a terminal emulator, they can use Replay. The AI Automation Suite handles the heavy lifting of component generation and test writing.

Can Replay handle non-web legacy systems?#

Yes. Whether it’s an AS/400 green screen via a terminal emulator, a Citrix-delivered Delphi app, or an old Java Swing client, if it can be displayed on a screen, Replay can extract it.

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