Building Hybrid Cloud UI Bridges: Connecting Legacy On-Prem Assets to Modern React Portals

The $3.6 trillion technical debt crisis isn't a coding problem; it's a translation problem. For the average enterprise, the distance between a legacy COBOL-based terminal and a modern React-based cloud portal is measured not in miles, but in months of manual documentation and failed "big bang" rewrites. Industry data shows that 70% of legacy rewrites fail or exceed their timeline, often because the institutional knowledge required to rebuild the system has long since left the building.

When enterprise architects talk about building hybrid cloud bridges, they are describing the structural necessity of maintaining operational continuity on-premise while delivering a modern, cloud-native experience to the end user. This isn't just about moving data; it’s about translating the complex, undocumented business logic trapped in legacy UIs into a scalable React ecosystem.

TL;DR: Modernizing legacy systems requires a "bridge" approach rather than a total rewrite. By using Replay for Visual Reverse Engineering, enterprises can reduce modernization timelines from 18 months to a few weeks. This guide covers the technical architecture of hybrid UI bridges, the role of automated documentation, and how to implement a React-based portal that communicates seamlessly with on-premise assets.

---

The Architectural Crisis: Why Manual Bridging Fails#

The average enterprise rewrite takes 18 months. During that time, the business requirements change, the original developers of the legacy system retire, and the "new" system is often outdated before it even launches. According to Replay’s analysis, 67% of legacy systems lack any form of up-to-date documentation, forcing architects to perform "archaeological coding" just to understand how a single screen functions.

Building hybrid cloud bridges manually typically involves a developer sitting with a subject matter expert (SME), recording notes on how a 20-year-old insurance claims screen works, and then attempting to replicate that logic in a modern component library. This process takes an average of 40 hours per screen.

Visual Reverse Engineering is the process of using video recordings of legacy user workflows to automatically generate documented React code, design systems, and architectural maps.

By shifting from manual observation to visual reverse engineering, teams can leverage tools like Replay to cut that 40-hour window down to just 4 hours.

---

Strategic Blueprints for Building Hybrid Cloud Bridges#

A successful hybrid bridge requires three distinct layers: the Legacy Persistence Layer (on-prem), the Mediation Layer (the bridge), and the Modern Experience Layer (React/Cloud).

1. The Inventory Phase: Mapping the Undocumented#

You cannot bridge what you do not understand. Before writing a single line of TypeScript, you must inventory the existing flows. This is where most projects stall.

Industry experts recommend a "Flow-First" approach. Instead of trying to map the entire database, map the user's journey. If a user needs to process a claim, record that specific workflow. Replay’s "Flows" feature allows architects to see the entire architectural path of a legacy transaction by simply recording the screen.

2. The Mediation Layer: API Gateways and Sidecars#

Building hybrid cloud bridges requires a robust middle tier. Since legacy systems often lack RESTful APIs, the bridge must often interact with terminal emulators or SOAP services.

3. The React Experience Layer#

The goal is to provide a "Single Pane of Glass." The user shouldn't know that their data is coming from a mainframe in a basement in Ohio.

---

Technical Implementation: The React Bridge Pattern#

When building hybrid cloud bridges, the most effective pattern is the Adapter Component Pattern. This allows you to build modern React components that wrap legacy data structures, providing a clean interface for the frontend while maintaining the "source of truth" in the on-premise system.

Below is an example of a React Hook designed to bridge the gap between a legacy on-premise XML feed and a modern React UI.

typescript
// hooks/useLegacyBridge.ts
import { useState, useEffect } from 'react';
import { transformLegacyData } from '../utils/dataMapper';

interface LegacyRecord {
  ID_VAL: string;
  CUST_NAME_EXT: string;
  ACC_BAL_CURR: number;
}

export const useLegacyBridge = (recordId: string) => {
  const [data, setData] = useState<ModernCustomer | null>(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    async function fetchFromOnPrem() {
      try {
        // Interfacing with an on-premise sidecar or proxy
        const response = await fetch(`https://internal-bridge.enterprise.com/api/v1/records/${recordId}`);
        const rawData: LegacyRecord = await response.json();
        
        // Transform undocumented legacy keys into clean React props
        const cleanData = transformLegacyData(rawData);
        setData(cleanData);
      } catch (error) {
        console.error("Bridge Connection Failed", error);
      } finally {
        setLoading(false);
      }
    }
    fetchFromOnPrem();
  }, [recordId]);

  return { data, loading };
};

This bridge pattern ensures that the React application remains decoupled from the legacy system's naming conventions (like

). By using Replay's Blueprints, these transformation maps are generated automatically during the recording phase, saving developers from manually mapping hundreds of obscure database fields.

---

Visual Reverse Engineering: The Engine of the Bridge#

Video-to-code is the process of capturing user interactions within a legacy application and using AI-driven automation to output functional React components that mirror the original business logic.

When you are building hybrid cloud bridges, the "Visual" aspect is critical. Legacy systems are often "state-heavy." A single button click might trigger five different validation rules that aren't documented anywhere.

According to Replay's analysis, capturing these "hidden" states visually is the only way to ensure 100% parity between the old system and the new bridge. Replay’s AI Automation Suite analyzes the recording, identifies the components (buttons, inputs, grids), and generates a Design System that matches the enterprise’s modern standards while retaining the legacy functionality.

Example: Generating a Modern Component from a Legacy Grid#

In the code block below, we see a React component generated to replace a legacy "Green Screen" data table. The logic for pagination and filtering is extracted from the visual recording.

tsx
// components/ModernClaimsGrid.tsx
import React from 'react';
import { useTable } from 'react-table';
import { LegacyBridgeProvider } from '@replay/bridge-sdk';

interface ClaimsGridProps {
  onRowClick: (id: string) => void;
}

const ModernClaimsGrid: React.FC<ClaimsGridProps> = ({ onRowClick }) => {
  // Logic extracted via Replay Visual Reverse Engineering
  const { claims, syncStatus } = LegacyBridgeProvider.useOnPremData('CLAIMS_MODULE_01');

  return (
    <div className="p-6 bg-white rounded-lg shadow-xl">
      <h2 className="text-xl font-bold mb-4">Active Claims Portal</h2>
      <table className="min-w-full divide-y divide-gray-200">
        <thead>
          <tr>
            <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase">Claim ID</th>
            <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase">Status</th>
          </tr>
        </thead>
        <tbody className="divide-y divide-gray-200">
          {claims.map((claim) => (
            <tr key={claim.id} onClick={() => onRowClick(claim.id)} className="hover:bg-gray-50 cursor-pointer">
              <td className="px-6 py-4 whitespace-nowrap">{claim.id}</td>
              <td className="px-6 py-4 whitespace-nowrap">
                <span className={`px-2 py-1 rounded ${claim.urgent ? 'bg-red-100 text-red-800' : 'bg-green-100'}`}>
                  {claim.status}
                </span>
              </td>
            </tr>
          ))}
        </tbody>
      </table>
      {syncStatus === 'syncing' && <p className="text-sm text-blue-500 mt-2">Updating from On-Prem Mainframe...</p>}
    </div>
  );
};

---

Security and Compliance in Hybrid Bridges#

For Financial Services, Healthcare, and Government sectors, building hybrid cloud bridges isn't just a technical challenge—it's a regulatory one. You cannot simply pipe mainframe data into a public cloud without rigorous controls.

Replay is built for these regulated environments. With SOC2 compliance and HIPAA-ready configurations, the platform allows for on-premise deployment. This means the visual reverse engineering process happens entirely within your firewall.

Key security considerations for hybrid bridges include:

• •Data Masking: Ensuring PII (Personally Identifiable Information) is never captured in the recording phase.
• •Identity Propagation: Carrying the user's on-premise credentials (LDAP/Active Directory) through to the React portal.
• •Audit Logging: Every interaction across the bridge must be logged to satisfy regulatory requirements.

For more on managing complex enterprise architectures, see our guide on Architecture Mapping for Legacy Systems.

---

The Workflow: From Recording to React#

The process of building hybrid cloud bridges with Replay follows a streamlined four-step workflow:

1. •Record: An SME performs a standard workflow in the legacy application. Replay captures the UI changes and the underlying data calls.
2. •Document: Replay’s AI Automation Suite generates a comprehensive "Blueprint" of the screen, including state transitions and component hierarchies.
3. •Generate: The platform outputs documented React code and a Component Library that matches your organization's design system (e.g., Tailwind, Material UI).
4. •Deploy: The new React components are integrated into the modern portal, connected to the on-premise assets via the bridge API.

This workflow eliminates the "Lost in Translation" phase where developers misunderstand the business logic of the original system. Because the code is generated directly from the visual truth of the legacy UI, the risk of regression is virtually zero.

---

Scaling the Bridge Across the Enterprise#

Once the first few "bridge" components are live, the focus shifts to scale. The goal is to move from a single portal to a unified enterprise design system.

When building hybrid cloud bridges at an enterprise scale, you often encounter "Shadow IT"—pockets of the organization using disparate legacy tools. By centralizing the modernization process in the Replay Library, you create a single source of truth for every UI component across the company.

This centralization is what allows a 70% time savings. Instead of rebuilding a "Date Picker" or a "Policy Search" component for every department, you reverse engineer it once and deploy it everywhere.

---

Frequently Asked Questions#

What are the main risks when building hybrid cloud bridges?#

The primary risks are data latency and logic mismatch. If the modern React UI expects data in a format the legacy system cannot provide quickly, the user experience suffers. Additionally, if the bridge doesn't account for the "hidden" validation rules in the legacy UI, you risk data corruption. Replay mitigates this by capturing the visual state changes that represent those validation rules.

How does Visual Reverse Engineering handle complex, multi-step workflows?#

Replay’s "Flows" feature is designed specifically for multi-step workflows. It records the transition between screens and documents the state that is passed from one "page" to the next. This allows architects to see the entire lifecycle of a transaction, ensuring the hybrid bridge supports the full end-to-end process.

Is Replay suitable for highly regulated industries like Healthcare?#

Yes. Replay is SOC2 compliant and offers on-premise deployment options to ensure that sensitive data never leaves your secure environment. We also provide data masking tools to strip PII from recordings before they are processed by our AI suite.

Can we use our existing Design System with Replay?#

Absolutely. Replay is design-system agnostic. You can feed your existing Figma tokens or React component library into the platform, and the generated code will utilize your specific styling, hooks, and components while maintaining the legacy system's logic.

How does this approach compare to a "Big Bang" rewrite?#

A "Big Bang" rewrite attempts to replace the entire system at once, which leads to a 70% failure rate. Building hybrid cloud bridges allows for an incremental, iterative approach. You can modernize one workflow at a time, delivering value to users in weeks rather than years, while maintaining the stability of your on-premise core.

---

Ready to modernize without rewriting? Book a pilot with Replay