Modernisation without disruption: Four ways to revitalise legacy applications
If you're leading digital transformation while managing legacy systems, you'll know the dilemma: how do you modernise effectively without disrupting essential services or breaking the budget?
Whether you're in the public sector or private enterprise, those established applications that power your essential operations can feel like a double-edged sword - critical to daily operations, yet frustratingly difficult to update or integrate with newer technologies.
The good news is that you don't need to choose between costly wholesale replacement and staying stuck with outdated systems. Increasingly, many organisations are discovering that a thoughtful, modular approach to modernisation delivers better outcomes - allowing you to upgrade incrementally based on what matters most to your operations and what's technically achievable within your constraints.
In this article, we explore four practical strategies that support this flexible 'pick-and-mix' approach to legacy modernisation, including real-world examples from our clients to show you exactly how these approaches work in practice and what kind of impact you can expect.
1. Access the data directly
One of the simplest and most effective ways to unlock value from legacy systems is to surface the data they contain. Tools like Power BI and the Power Platform suite allow you to connect directly to legacy databases, enabling the creation of dashboards, reports, and even new data capture forms.
This approach was successfully used by a multi-national manufacturer of tools and hardware that needed to improve visibility across its global operations. By using Power Platform tools to interrogate legacy data, the organisation was able to build real-time reporting dashboards without altering the underlying application logic.
However, caution is essential. Writing new data into legacy databases must be done with safeguards in place to preserve auditing, security, and business rules.
2. Build an API layer over the application
For systems with complex business logic that must remain intact, wrapping legacy functionality in an API layer can be transformative. This allows modern interfaces and external systems to interact with legacy applications while leaving proven workflows intact.
This strategy is particularly useful in public sector environments, where legacy systems often contain decades of embedded rules and workflows. By exposing functionality through APIs, organisations can build new services and user experiences while maintaining the integrity of the original system.
A practical example of this approach is our work with the Isle of Man Ship Registry, where we developed an offline survey application that leveraged APIs to access existing business logic and data layers. The result was a modern, user-friendly interface for ship surveyors that preserved all the established regulatory processes and data integrity of the original system.
3. Progressive replatforming
Instead of replacing an entire system in one risky leap, progressive replatforming involves cataloguing system functionality and incrementally replacing high-priority features with modern equivalents. Each new module runs in parallel with the legacy system until it’s validated and ready to take over, reducing disruption and risk.
We used this approach in a project we undertook with a UK-based hardware manufacturer who exports its products worldwide. They wanted to modernise their ERP system but after initially considering a full replacement, they realised the disruption and risk were prohibitive. Instead, we worked with them to migrate key components from Visual Basic to C#, replatforming onto a supported .NET framework. This preserved critical business logic, reduced licensing costs, and improved the user experience.
4. Code conversion
In extreme cases, especially where legacy code is poorly documented or too complex to reverse engineer, automated code conversion may be the only viable option. Tools like GitHub Copilot can help translate legacy languages (e.g. COBOL) into modern equivalents like C#.
We are currently working on a major modernisation project to replace a complex but critical system for the Isle of Man Government. Due to a multitude of factors including the age and underlying technology of the existing system, a rewrite was required. However, for some small sections of existing business logic, the most viable way of accurately recreating the equivalent logic was to use Copilot to directly convert the COBOL to C#. While this approach carries risk, it can be mitigated using a comprehensive suite of automated “unit” tests to validate functional parity.
Getting started: Understand before you act
Whatever modernisation path you choose, there's one crucial step that always comes first: getting to know your existing systems inside and out. This means:
- Understanding how everything connects
- Identifying which functions are essential to your operations, and
- Working closely with your stakeholders to agree on what success looks like
In our experience, documented in the PDMS whitepaper on Legacy Modernisation, the most successful projects start with absolute clarity. You need to understand your business objectives, know your technical limitations, and really grasp what your users need from the system.
The best way to achieve this clarity? Roll up your sleeves and dive into workshops, stakeholder interviews, and comprehensive system audits during your discovery phase.
It may feel time-consuming, but this upfront investment in understanding will save you countless headaches later and ensure your modernisation efforts actually deliver the results you're looking for.
That said, we recognise that not every organisation has the internal resources or expertise to tackle this discovery phase effectively. If you're feeling overwhelmed by where to start or need guidance on structuring your approach, our Digital Foundations Framework provides a proven methodology for working through these critical early stages. It's designed specifically to help teams navigate the complexities of legacy assessment and modernisation planning, giving you the confidence and clarity you need to move forward successfully.
Conclusion
The beauty of legacy modernisation is that it doesn't have to be an all-or-nothing gamble. By taking a thoughtful ‘pick-and-mix' approach, you can strike the right balance between innovation and stability - reducing risk while delivering real value to your users along the way.
Whether you're accessing data more effectively, building modern APIs, gradually replatforming, or converting existing code, the goal remains the same: modernise in a way that fits your context, respects your existing strengths, and sets you up for the future.
With the right framework and support, legacy systems aren't holding you back - they can become the foundation for your next stage of innovation.
To find out more about how you can modernise your legacy systems, visit our Digital Foundations Framework page or Legacy Modernisation Services
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