Many entrepreneurs equate 'Legacy' systems simply with old code, but the definition goes much deeper. A Legacy system is often software that has been successful and makes money for the company, but over the years has become a brake on growth. Lack of documentation, outdated libraries, or code that no one on the current team understands means that every change comes with a paralyzing fear of failure. Paradoxically, the more important the system is to your business, the harder it is to decide to modernize it.
The hidden cost of doing nothing
Technical debt works exactly like financial debt — you have to pay interest on it. In the IT world, this interest is a drastically slower 'time-to-market'. Features that your competitors deploy in days require weeks of analysis and manual testing for you. There is also another, often overlooked cost: employee turnover. In 2025, talented developers want to work with modern technologies. Forcing them to maintain outdated, 'toxic' code is the fastest way to lose the best people on your team.
The big bang rewrite trap
The most common reaction to Legacy system problems is the temptation to bulldoze everything and write the system from scratch. In the industry, we call this 'The Big Bang Rewrite', and it is a strategy that almost always ends in failure. The problem is that the old system doesn't stand still — it still has to serve customers and evolve. The new system, being created in parallel, is therefore chasing a moving target. As a result, after a year, the company ends up with two systems: the old one, which still works (because it has to), and the new one, which still lacks key functionalities. This is a waste of resources that few can afford.
The strangler fig pattern: evolution instead of revolution
At MQS, we use a much safer approach known as the 'Strangler Fig Pattern'. The inspiration here is nature — the fig tree wraps around an old tree, gradually replacing it. In software, this means building new functionalities as independent microservices around the old system, rather than inside it. New modules take over traffic piece by piece. Over time, the old monolith becomes smaller and less relevant until it can finally be safely turned off. This allows for delivering business value from the first day of modernization without the risk of operational paralysis.
Refactoring vs. rewriting
The key to success is the ability to assess which parts of the system are worth saving and which need to be replaced. Not all old code is bad. Sometimes deep refactoring — improving the code structure without changing its behavior — is enough to restore its readability and flexibility. However, if a module is based on technology that is no longer supported, or its logic is completely incomprehensible, it is safer to 'cut it off' and write it as a new, external service.
Safety of changes
You cannot modernize something you cannot measure. Before introducing any changes to a Legacy system, at MQS we always start by building a safety net in the form of automated tests. They give us the certainty that by cleaning up code in one place, we haven't broken a critical business process in another. Without tests, modernization is gambling, and we don't believe in gambling in business.
Do you have a system whose development has become a nightmare? At MQS, we are not afraid of difficult projects. We specialize in taking over and 'healing' code left by others. Contact us, and we will prepare a recovery plan for your software.