Modernization Strategies for Legacy Systems: Choosing the Right One for Your Project

Modernization strategies for legacy systems: Choosing the right one for your project

We have already described the way to analyze the legacy system and evaluate risks before running a modernization process. In this article, we want to share our insights on how to build a strategy that will help you to overcome all pitfalls. So, if your product for some reason has become determined as a legacy system, you can figure out what options you have.

Legacy systems are tricky to update and it can be a costly project. However, there are some ways to overcome potential pitfalls and save the resources of the development team and money for the customer. In this article, we are going to explain how to choose the right approach to modernize your legacy system and come up with a solution that is able to satisfy business needs.

Four Basic Legacy Software Modernization Strategies

There are four basic approaches to legacy system modernization. If you want to run a modernization you can rewrite the whole system from scratch, continue work with the project in the old mode, build a new app over the old version, or make partial refactoring for certain parts of the legacy software.

When choosing the right one to develop your software, you need to analyze the current state of the system and the specifics of the legacy code; the business needs and tasks the new system should be able to cope with; as well as time and money resources needed to improve the existing software or create a new product from scratch.

After this analysis, we can choose the most reasonable development strategy for the legacy system migration and modernization.

#1 Rewrite the Whole System

Rewriting the system from scratch makes sense in the following cases:

  • The system doesn’t work at all or it works so badly that users abandon it.
  • The customer understands that he is going to pay for the legacy system and for the software created from scratch.
  • The system wasn’t used at all, maybe it was just a prototype for proof of concept.

There are pros and cons to this strategy that you should take into account.


  • After the legacy code analysis, the developer can find out what mistakes were made and come up with ways to avoid them.
  • Coding from scratch is more enjoyable for the development team since it is always easier to work with your own code.
  • If there are some good practices utilized by the legacy system, the developer will be able to reuse them thereby saving time and money.


  • Writing code from scratch can take a lot of time and can be expensive.
  • If the system is currently in use it is necessary to support the legacy and new versions until all of the users migrate to the new one.
  • There may also be some hidden issues with the legacy system which may take more time and money than initially estimated.

#2 Continue Work in the Same Style

You may also decide to continue development according to the principles and structures embedded in the legacy system. This approach to modernizing legacy systems makes sense when the code initially created is good enough, the system is too complex to be rebuilt from scratch, or the customer has no time, money, or desire to make significant changes, and only wants to fix the critical mistakes.

In the latter situation, continuing work in the same style is the most reasonable choice if the customer thinks it can generate profits that can be reinvested in creating more advanced software in the future.

Here are the pros and cons of dealing with legacy systems this way.


  • The system continues to work while the developer adds new features.
  • The customer sees the improvements made right from the beginning of the process.


  • Sometimes adjustments make the system even more complex and difficult to deal with.
  • There is a need to have very strong technical skills and experience in solving problems with legacy systems. Otherwise, there is a chance of canceling out all the changes at the final stage.

#3 Create a New Application Over the Old One

This is one of the most difficult legacy modernization techniques. What’s more, it requires a very careful analysis of the already developed code and functionality since the essence of the approach is to add the new features over the old ones. This way of modernizing the legacy system is reasonable if the system works well, and if it is necessary to expand functionality only.

However, it is always necessary to take all the pros and cons into account.


  • The legacy system continues its work while the new features are added.
  • It is possible to take advantage of the positive aspects of the legacy system while creating new functionality for it.
  • The customer will see the result of his investments immediately.


  • If there were mistakes in the legacy code, it is necessary to find and fix them before developing new features.
  • With a complex and confusing legacy architecture, this approach can be difficult and costly to implement.
  • In the case of an unforeseen situation (for example, if the project is no longer financed), there is a risk of getting an even more complex legacy system.

#4 Partial Refactoring

If it’s impossible to create a new application over the old one and the code cannot be left in its current state, then it is necessary to do a gradual refactoring and redesign of the entire system. To do this, we isolate parts of the system, allocate independent modules, and rewrite them. Thus most of the system will be rewritten according to the gradual legacy system replacement strategy. This way of legacy modernization will be suitable if the system has great value for customers and most of its functions already work well.

Here are the main pros and cons of this approach:


  • The users are still able to use the system with occasional updates.
  • It is possible to plan the updates and come up with new features gradually.


  • It is not always possible to debug the system in the modules.
  • The speed of refactoring will be stable, but it may be too slow for the customer.

Building a Development Process on a Legacy Project: Pitfalls You Need to Overcome

How do you manage legacy systems? The answer is specific to the project requirements. However, we have some practice-proven tips that allow us to build a legacy system modernization process wisely.

Team Building

It is necessary to make sure that all team members have the expertise needed to deal with the potential pitfalls of legacy systems. They should have analytical and critical thinking skills in order to foresee the consequences of the changes. What’s more, team members should be ready to deal with incomprehensable code.

Sometimes, a representative of the customer who was involved in the legacy system development joins the new team. In this case, it is necessary to be very careful since there is a risk of making the same mistakes again under pressure from the customer.

Communication and Task Management

The process of communication should be established very clearly. While working with legacy systems, there is a need to manage tasks even more carefully with the help of Jira or other task management software. Each task should reflect the current state of the system, plus it should be clearly stated what should be done next.

As for communication issues, all team members should check the work of others on the team, and remind each other about the best practices of dealing with legacy software according to the chosen strategy.

Critical Moments

There are also some additional moments worth noting.

  • First, there is no point in choosing a fixed price contract while working with legacy systems. It should be replaced with a time and material contract.
  • Second, it is necessary to be very careful with time and money estimates since legacy systems are unpredictable.
  • Third, legacy system modernization requires keeping the current business tasks of the customer in mind. When implementing any change, it is always necessary to evaluate the effect on the customer’s business process. What’s more, you should always be ready for unforeseen circumstances like the sudden failure of the system in the middle of the night. That is why it makes sense to have highly responsible team members who will be able to quickly deal with a critical issue at any time.


The insights to legacy systems modernization that we’ve shared in this article are our proven practices. Our tech-savvy team has a lot of experience dealing with these kinds of specific projects.