Modernizing Global Supply Chains: Moving from AS/400 Without the "Big Bang" Risk

The global supply chain runs on code written before the internet existed. In 2024, an estimated $3.6 trillion in technical debt is locked inside "black box" legacy systems, with the IBM AS/400 (now IBM i) sitting at the epicenter. For global logistics, manufacturing, and retail giants, these systems are both the backbone of operations and the single greatest bottleneck to innovation.

The traditional approach to modernizing global supply infrastructure involves a "Big Bang" rewrite—an 18-to-24-month odyssey that carries a staggering 70% failure rate. When these projects fail, they don't just lose money; they paralyze shipping lanes, freeze inventory, and decimate quarterly earnings.

TL;DR: Modernizing global supply systems no longer requires high-risk 'Big Bang' rewrites; visual reverse engineering via Replay allows teams to extract business logic from AS/400 workflows into documented React components in weeks, reducing manual effort by 90%.

The Archeology Problem: Why 67% of Systems Lack Documentation#

The primary obstacle in modernizing global supply chains isn't a lack of modern tools; it's a lack of understanding of the existing ones. Our research shows that 67% of legacy systems lack any form of up-to-date documentation. In the context of an AS/400 environment, the business logic is often buried in decades-old RPG (Report Program Generator) code, maintained by developers who are rapidly approaching retirement.

When an Enterprise Architect is tasked with "modernizing," they usually start with "Software Archaeology." This involves:

1. •Sifting through thousands of lines of undocumented RPG or COBOL.
2. •Interviewing end-users to guess what the "green screen" actually does.
3. •Manually mapping terminal inputs to modern database schemas.

This manual process takes an average of 40 hours per screen. For a global supply chain application with 500+ screens, you are looking at years of discovery before a single line of modern code is written.

Visual Reverse Engineering: Turning Video into Truth#

The future of modernization isn't rewriting from scratch—it's understanding what you already have. Replay introduces a paradigm shift: Visual Reverse Engineering.

Instead of reading the code to understand the behavior, Replay records real user workflows as they interact with the legacy AS/400 terminal. By capturing the state changes, data inputs, and UI transitions, Replay’s AI Automation Suite extracts the underlying business logic and generates documented React components and API contracts.

💡 Pro Tip: Don't start by looking at the source code. Start by looking at the execution. The legacy system's behavior during a "Create Bill of Lading" workflow is the only source of truth that matters.

From Green Screen to React: The Technical Bridge#

When we modernize a supply chain module—for example, an Inventory Reconciliation screen—we aren't just "skinning" the terminal. We are extracting the functional requirements. Replay analyzes the recording and generates a "Blueprint" that defines the data model and the component architecture.

typescript
// Example: Replay-generated API Contract for Legacy Inventory Sync
// Extracted from AS/400 'WRKOBJ' and 'INV001' workflows

export interface InventoryUpdateContract {
  sku_id: string;          // Extracted from Field 001 (Row 4, Col 12)
  warehouse_code: string;  // Extracted from Field 002 (Row 5, Col 12)
  quantity_on_hand: number;
  last_audit_date: string; // ISO format converted from legacy CYYMMDD
  status_code: 'A' | 'I' | 'S'; // Active, Inactive, Suspended logic preserved
}

/**
 * Generated E2E Test Case
 * Validates that the modern React frontend replicates the 
 * legacy validation logic for quantity thresholds.
 */
describe('Inventory Reconciliation Flow', () => {
  it('should trigger "Low Stock" alert exactly like legacy screen INV001', () => {
    // Logic extracted from RPG indicator 44
    const legacyThreshold = 10;
    expect(calculateAlert(9)).toBe(true);
  });
});

The 3-Step Extraction Process#

Modernizing global supply operations requires a systematic approach that avoids the "black box" trap.

Step 1: Workflow Recording#

Users perform their standard daily tasks—processing orders, updating shipping statuses, or managing vendor manifests—while Replay records the session. This isn't a simple screen recording; it's a capture of the DOM (or terminal state), network calls, and state transitions.

Step 2: Blueprint Generation#

The Replay AI Automation Suite processes the recording. It identifies patterns: "This input always requires a 10-digit numeric string," or "This button click triggers a synchronous call to the ledger." It generates a Blueprint—a platform-agnostic representation of the business logic.

Step 3: Component and API Synthesis#

Using the Blueprint, Replay generates high-quality React components that match your organization's Design System (via the Replay Library). Simultaneously, it generates the API contracts required to connect the new frontend to your existing (or modernized) backend.

💰 ROI Insight: Manual screen modernization takes ~40 hours. With Replay, the same screen is extracted, documented, and generated in ~4 hours. For a 200-screen project, this saves 7,200 man-hours.

Preserving Business Logic in Regulated Environments#

Global supply chains often intersect with highly regulated sectors: Healthcare (HIPAA), Financial Services (SOC2), and Government. A "blind" rewrite is a compliance nightmare. If the legacy system had a specific validation rule for shipping hazardous materials, and that rule is missed in the rewrite, the company faces massive legal liability.

Replay ensures Logic Preservation. Because the modern code is generated directly from the observed behavior of the legacy system, the "hidden" rules are captured.

⚠️ Warning: Never assume the legacy documentation is correct. In 90% of AS/400 environments, the "real" business logic exists in patches and "hotfixes" applied directly to the production environment over decades.

Implementation Detail: Handling Legacy Data Formats#

One of the biggest pain points in modernizing global supply is data transformation. AS/400 systems often use EBCDIC encoding or specific date formats like

. Replay's extraction engine automatically identifies these patterns and generates the necessary transformation logic in the modern stack.

typescript
// Replay-generated utility for legacy date conversion
// Preserves the "C" (Century) bit logic found in AS/400 schemas

export function fromLegacyDate(legacyDate: number): string {
  // AS/400 format: 1230101 (where 1 = 2000s, 0 = 1900s)
  const dateStr = legacyDate.toString();
  const centuryBit = parseInt(dateStr.substring(0, 1));
  const year = (centuryBit === 1 ? 2000 : 1900) + parseInt(dateStr.substring(1, 3));
  const month = dateStr.substring(3, 5);
  const day = dateStr.substring(5, 7);
  
  return `${year}-${month}-${day}`; // Returns standard ISO 8601
}

Eliminating Technical Debt with Automated Audits#

The $3.6 trillion technical debt problem isn't just about old code; it's about unknown code. Replay's Technical Debt Audit feature provides CTOs with a heat map of their legacy environment.

• •Red Zones: High-complexity screens with zero documentation and high user traffic.
• •Green Zones: Low-complexity workflows already successfully mapped to modern components.

This visibility allows VPs of Engineering to prioritize modernization efforts based on actual business impact rather than guesswork. Instead of a 2-year rewrite of the whole system, you can modernize the "Order Entry" flow in 3 weeks, providing immediate value to the business.

The Future: From Black Box to Documented Codebase#

The "Modernize without rewriting" philosophy acknowledges a hard truth: the legacy system works. It has survived decades of edge cases, market shifts, and scale. The goal isn't to destroy it; it's to liberate the logic trapped inside it.

By using Replay, enterprise teams move from a state of "Software Archaeology" to "Visual Engineering." You stop guessing what the AS/400 is doing and start seeing it as a documented, manageable asset.

• •Library: House your modern React components that mirror legacy functionality.
• •Flows: Map the end-to-end architecture of your supply chain.
• •Blueprints: Edit the logic visually before generating code.
• •AI Automation: Let the machine handle the tedious mapping of 5,000 fields.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual rewrite takes 18-24 months, Replay typically reduces this to 2-8 weeks for a standard enterprise module. The extraction of a single complex screen, including documentation and React component generation, takes approximately 4 hours.

What about business logic preservation?#

Replay uses "Video as source of truth." By recording actual execution, we capture the "hidden" logic—indicator variables, specific validation rules, and error handling—that is often missing from the source code documentation.

Does Replay support on-premise deployments?#

Yes. For industries like Government, Financial Services, and Manufacturing, we offer on-premise installations to ensure that sensitive supply chain data never leaves your secure environment. We are SOC2 and HIPAA-ready.

Can Replay handle complex AS/400 "Green Screens"?#

Absolutely. Replay's engine is specifically designed to interpret terminal emulation protocols and map them to modern web architectures, converting fixed-position fields into responsive, accessible React forms.

---

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