How to build away from legacy
Author : Craig Cook, Catapult
10 April 2025
Craig Cook, Chief Engineer at Catapult CX
When it comes to managing their IT, many organisations are hindered by legacy. Don’t go for a complete overhaul, upgrade legacy systems incrementally, says Craig Cook, Chief Engineer at Agile consultancy Catapult.
These aren’t systems that are ‘old’, they’re ones where maintenance and tech debt have built up to a point where changing the system will become too expensive and risky.
Working with legacy systems has become a challenge for many businesses. Usually, it’s legacy software that is running a company and bringing in all the revenue, so it’s important that companies don’t throw the baby out with the bath water when upgrading.
However, even once cutting-edge software can quickly become a barrier to rolling out new features to grow and retain customers. Many large organisations rely on outdated architecture that’s holding them back. According to a report from Dell, over 70 percent of software used by Fortune 5000 companies was developed 20 or more years ago.
By building a minimum viable replacement (MVR) to replace legacy digital services, businesses can develop the necessary features to replace existing products, and without breaking the existing business. In cases where the commercial or legal situation prevents updating the existing product, a full replacement is required. User feedback will help refine and improve the software, and help engineers prioritise new features and next steps. This is a similar process to that used with minimum viable products (MVPs), which usually targets customer acquisition.
1. Find the minimum
When building on an MVP, businesses are adding functionality and trying to attract new customers. However, most legacy systems or products have an established user base, so the aim is to retain and migrate these customers to the new system with minimal churn. Therefore, companies should identify the bare minimum changes that they can make without breaking the business. Therefore, with MVRs, companies usually focus on replacing (or enhancing) existing functionality and fixing bugs.
For a good example of feature enhancement, look at Microsoft Internet Explorer (IE). Microsoft ended support for all versions of IE before version 11 in January 2020, ending support for IE11 in June 2022. To provide continuity, Microsoft developed IE mode in its Edge browser so that customers could continue to access applications and websites that still rely on IE.
2. Identify a migration path
Ultimately, the aim is to minimise disruption to the existing business and, to do this, companies must identify a migration path to ensure all customers move to the new digital technologies. There are various ways that companies can structure their migration paths. For example, is it possible to replace a legacy system feature by feature or does it need to be done in one go? Could the company migrate users based on persona? For example, starting by migrating new customers and then existing ones?
Businesses can start by looking at which customer groups make up the majority of users and identify their pain points and priorities. For example, if a bank is launching a new app to replace a previous version, it could review its customer database and discover that most users are mortgage customers. Using this information, it may enhance its digitalisation of services by allowing people to apply for mortgages within the new app.
3. Update in increments
When updating a legacy system, keep each stage as simple as possible by making minor enhancements to improve UX. Upgrading legacy systems in small manageable increments can help businesses avoid the high costs and risks of a complete system overhaul. This gradual approach can also provide much-needed stability, allowing companies to stay up-to-date with modern technology while minimising disruptions.
We took this approach when helping the Maritime Coastguard Agency (MCA) digitise its UK Ship Register (UKSR) services. Using infrastructure-as-code (IaC), we built a microservices platform that the MCA could use to securely provide access to its data and run any new digital services it wanted to create for customers. We delivered the first digital services in nine weeks, and, over the following months, deployed additional microservices – digitising the rest of the UKSR and Beacons services.
Building an MVR can help companies move away from outdated legacy systems, and this means focusing on enhancing features and using an incremental approach to update it over time. Working with a reliable software partner can help – an experienced, hands-on consultant can help you digitise and adapt to changing customer needs.
Are you interested in updating your legacy system? If so, contact Catapult CX; our experienced team can support you through the legacy migration process.
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