Making Sense of the 5 R’s of Legacy Modernisation – A Practical Path to Legacy System Modernisation

For many organisations, CA Gen (formerly IEF, COOL:Gen, Advantage Gen) has been the foundation of their most critical business systems for decades. These platforms have powered finance, insurance, public sector, and operational systems with remarkable reliability. 

But in today’s digital-first world, that stability now hides mounting inefficiencies. The challenge isn’t that Gen doesn’t work, it’s that it no longer keeps pace with evolving business needs, integration demands, and user experience expectations. 

As a result, many teams are now exploring Gen modernisation as part of a wider legacy software modernisation or legacy IT modernisation strategy. The goal isn’t to discard the past, but to modernise it thoughtfully, strategically, and with minimal risk. 

Understanding the 5 R’s of Legacy Modernisation 

The 5 R’s framework provides a structured, low-risk path to modernise legacy IT and move beyond outdated dependencies. Each “R” represents a potential strategy for your Gen applications, and the right choice depends on your organisation’s goals, risk appetite, and technical landscape.

Rehost – “Lift and Shift”

Rehosting is often the first step in legacy system modernisation, moving Gen applications from costly mainframes to modern infrastructure, cloud or distributed environments. 

• Why it matters: Reduces operational costs and removes infrastructure constraints. 
• Best for: Stable systems with low change frequency but high maintenance costs. 

Refactor – Modernise the Codebase

Refactoring converts Gen-generated code into maintainable languages such as COBOL, Java or .NET. 

• Why it matters: Enhances maintainability, scalability, and integration with digital platforms. 
• Best for: Applications that must evolve quickly to support digital services and automation. 

Revise – Update Workflows and Interfaces

Revising focuses on improving business processes, user interfaces, and integrations without fully rewriting the application. 

• Why it matters: Increases usability and efficiency while reducing disruption. 
• Best for: Systems needing incremental improvements or modernised front-end capabilities. 

Rebuild – Re-architect for Modern Platforms

Rebuilding involves redesigning Gen applications using modern architectures, such as microservices, APIs, or cloud-native platforms. 

• Why it matters: Unlocks agility, scalability, and innovation potential. 
• Best for: Organisations undergoing digital legacy modernisation or adopting cloud strategies. 

Replace – Start Fresh

In some cases, retiring the Gen application and replacing it with a new or SaaS-based solution is the most strategic option. 

• Why it matters: Eliminates legacy constraints and enables full digital alignment. 
• Best for: Systems where ongoing support and integration costs outweigh their current value. 

Balancing Risk and Value in Legacy IT Modernisation 

Successful legacy application modernisation doesn’t happen in a single step. Many organisations begin with rehosting or replatforming to stabilise costs and reduce technical risk before moving on to refactoring or rearchitecting. 

This phased approach helps teams balance legacy modernisation risks with tangible business value. The aim is not simply to replace Gen, but to preserve what works while creating a sustainable path forward. 

A structured legacy modernisation evaluation can identify which “R” applies to each application, ensuring that every decision aligns with business goals, technical feasibility, and budget priorities. 

From Apprehension to Action 

Modernising legacy software can feel daunting, especially when those systems have been running reliably for decades. But the cost of inaction, skill shortages, escalating support contracts, and integration challenges, is far greater. 

The 5 R’s provide a clear, proven framework to modernise legacy IT systems with confidence. Whether you start by assessing your Gen environment or take your first step toward transformation, the path forward is clearer and safer than you might think. 

Our rapid discovery exercise will clarify your modernisation options, timelines, and costs, providing the insight and confidence to plan for what can be an exciting new stage in your organisation’s evolution.