Visual Event-Driven Architecture Mapping: Discovering the Hidden Logic of Legacy

The $3.6 trillion technical debt crisis isn't caused by bad code; it's caused by invisible code. In the average enterprise environment, 67% of legacy systems lack any form of up-to-date documentation, leaving architects to guess how data flows from a 30-year-old mainframe to a modern web portal. When you click "Submit" on a legacy insurance portal, you aren't just triggering a function; you are initiating a cascade of undocumented side effects across disparate microservices, message queues, and databases.

Modernization fails because we try to rewrite what we don't understand. Industry experts recommend that before a single line of new code is written, a comprehensive visual eventdriven architecture mapping must be performed to surface the "hidden logic" buried in user workflows.

TL;DR: Visual event-driven architecture mapping is the process of recording and documenting the causal relationships between UI actions and backend events. By using Replay, enterprises can automate this discovery phase, reducing the time to map a single screen from 40 hours to just 4 hours. This approach mitigates the risk of the 70% of legacy rewrites that typically fail by providing a high-fidelity blueprint for modernization.

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The Cost of the "Black Box" Problem#

Every legacy system eventually becomes a black box. The original developers have retired, the documentation was lost in a Confluence migration five years ago, and the source code is a labyrinth of "spaghetti events." According to Replay’s analysis, the average enterprise rewrite timeline stretches to 18 months primarily because teams spend the first six months simply trying to understand what the current system actually does.

Visual eventdriven architecture mapping solves this by treating the user interface as the primary source of truth. By observing how a system responds to real-world stimuli, we can reverse-engineer the event schema that governs the business logic.

Video-to-code is the process of converting visual recordings of user interactions into structured technical documentation, React components, and event-driven architectural diagrams.

The Anatomy of an Undocumented Event#

In a legacy Java or .NET monolith, an event isn't always a clean "Message" on a bus. It might be a database trigger, a global state change, or a synchronous call to a third-party API that isn't logged anywhere. Without visual eventdriven architecture mapping, these dependencies remain hidden until they break in the new environment.

Learn more about modernizing legacy UI to see how visual discovery prevents these breaks.

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Why Manual Mapping Fails the Enterprise#

Traditionally, architects mapped systems through "Event Storming" sessions—sticky notes on a whiteboard. While valuable for new builds, this is disastrous for legacy systems because it relies on human memory, which is notoriously unreliable for systems built decades ago.

When you use Replay, you aren't just taking screenshots; you are performing Visual Reverse Engineering. You record a workflow—like a claims adjuster processing a complex settlement—and Replay's AI Automation Suite extracts the component hierarchy and the event triggers associated with every interaction.

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Implementing Visual Event-Driven Architecture Mapping#

To effectively map a legacy system, you must bridge the gap between the DOM (Document Object Model) and the underlying event bus. This requires a structured approach to capturing state transitions.

Step 1: Capturing the Event Trigger#

First, we identify the interaction. In a legacy environment, this might be a

event on a non-semantic that acts as a button.

typescript
// Example: Mapping a Legacy Event Trigger to a Modern Event Schema
interface LegacyEventCapture {
  sourceElement: string;
  legacyAction: string;
  payload: Record<string, any>;
  timestamp: number;
}

const mapLegacyToModern = (event: LegacyEventCapture) => {
  return {
    type: "CLAIM_SUBMITTED",
    metadata: {
      originalElement: event.sourceElement,
      capturedAt: new Date(event.timestamp).toISOString(),
    },
    data: {
      ...event.payload,
      status: "PENDING_REVIEW"
    }
  };
};

Step 2: Generating the Visual Blueprint#

Once the events are captured via Replay's "Flows" feature, the platform generates a blueprint. This blueprint serves as the bridge between the recording and the final React code. Instead of a developer manually writing a

hook to handle a legacy side effect, Replay generates a documented component that mirrors the original behavior but uses modern best practices.

Step 3: From Flow to React Component#

The final stage of visual eventdriven architecture mapping is the output of clean, functional code. Below is an example of a component generated by Replay after analyzing a legacy data-entry flow.

tsx
import React, { useState } from 'react';
import { Button, Input, Card } from '@/components/ui-library';

/**
 * Generated via Replay Visual Reverse Engineering
 * Legacy Ref: Insurance_Portal_v4_Screen_09
 * Logic: Event-driven mapping for claim validation
 */
export const ClaimForm: React.FC = () => {
  const [isProcessing, setIsProcessing] = useState(false);

  const handleLegacySubmit = async (data: any) => {
    setIsProcessing(true);
    // Replay identified this event sequence from the recording:
    // 1. ValidateLocalState
    // 2. TriggerMainframeSync (Event ID: 0x88)
    // 3. UpdateUIState
    console.log("Mapped Event: CLAIM_SUBMITTED", data);
    setIsProcessing(false);
  };

  return (
    <Card className="p-6 shadow-lg">
      <h2 className="text-xl font-bold">Submit Claim</h2>
      <div className="space-y-4 mt-4">
        <Input placeholder="Policy Number" />
        <Button 
          onClick={handleLegacySubmit} 
          disabled={isProcessing}
        >
          {isProcessing ? 'Syncing with Mainframe...' : 'Submit'}
        </Button>
      </div>
    </Card>
  );
};

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The Role of AI in Event Discovery#

According to Replay's analysis, AI-driven automation is the only way to tackle the $3.6 trillion technical debt at scale. Manual code reviews are too slow, and automated static analysis tools often miss the "why" behind an event.

Visual eventdriven architecture mapping uses AI to look at the behavior of the application. By analyzing video recordings, the AI can identify patterns that suggest a specific architectural pattern—such as a Saga or a Command-Query Responsibility Segregation (CQRS) model—even if the underlying code is a mess of procedural scripts.

Identifying "Ghost Events"#

A "Ghost Event" is a backend process that occurs without a direct UI trigger (e.g., a scheduled batch job or a background sync). By mapping the UI state before and after these silent periods, Replay helps architects discover these hidden dependencies. This is critical for industries like Financial Services and Healthcare, where data integrity is non-negotiable and SOC2/HIPAA compliance is required.

Read about automated UI documentation to understand how AI bridges the gap between recording and code.

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Strategic Benefits for Regulated Industries#

For organizations in Government, Telecom, or Insurance, the stakes of modernization are higher. A failed rewrite isn't just a budget overrun; it's a regulatory nightmare.

1. •Auditability: Replay provides a visual audit trail of the legacy system's behavior. If a regulator asks why a certain calculation was performed, you can point to the recorded workflow and the mapped event logic.
2. •Risk Mitigation: By mapping 100% of the UI flows before starting the rewrite, you ensure that no edge cases are missed. This is how Replay helps teams achieve 70% time savings.
3. •On-Premise Security: For sensitive environments, Replay offers on-premise deployment options, ensuring that recordings of legacy systems never leave the internal network.

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The Methodology: How to Start Mapping Today#

If you are a Senior Enterprise Architect tasked with a massive modernization project, follow this 4-step methodology for visual eventdriven architecture mapping:

1. The Recording Phase#

Capture real user workflows using Replay. Don't just record the "happy path." Record the errors, the edge cases, and the weird workarounds that users have developed over the last decade.

2. The Extraction Phase#

Use Replay’s Library and Blueprints to extract the UI components and the event triggers. This phase turns raw video into a structured "Design System" and "Flow Architecture."

3. The Validation Phase#

Compare the mapped events against the existing source code. This is where you discover the "hidden logic." If the visual mapping shows an event that the code analysis missed, you’ve found a critical dependency.

4. The Generation Phase#

Export the mapped flows into documented React code. This code is now ready to be integrated into your modern microservices architecture, with all the legacy event logic preserved but modernized.

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Frequently Asked Questions#

What is visual event-driven architecture mapping?#

It is the process of using visual recordings of user interactions to discover, document, and map the underlying events and business logic of a legacy system. It bridges the gap between what a user sees and what the backend executes, creating a blueprint for modernization.

How does Replay handle sensitive data during recording?#

Replay is built for regulated environments and is HIPAA-ready and SOC2 compliant. It includes features for PII (Personally Identifiable Information) masking and offers on-premise deployment options so that sensitive data never leaves your secure environment.

Can Replay map events from mainframes or terminal-based systems?#

Yes. Because Replay uses Visual Reverse Engineering, it doesn't matter if the backend is a 40-year-old COBOL mainframe or a modern Node.js API. If the interaction is visible on a screen, Replay can map the workflow, document the logic, and help transition it to a modern React-based architecture.

How does this differ from standard screen recording?#

Standard screen recording is just a video file. Replay’s visual eventdriven architecture mapping converts that video into structured data: React components, TypeScript interfaces, and architectural diagrams. It understands the DOM structure and the causal relationships between actions.

Why is manual mapping considered a high-risk activity?#

Manual mapping relies on human interpretation and incomplete documentation. With 67% of legacy systems lacking docs, developers often miss hidden side effects. This leads to the 70% failure rate in legacy rewrites. Replay provides an objective, data-driven alternative.

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Ready to modernize without rewriting? Book a pilot with Replay