Technologies | March 17, 2023

Legacy system modernization – pros and strategies

It sometimes turns out that software or technology which has been developed over a long period of time cannot be changed for various reasons. It is then described as a “legacy system.” Some organizations use such systems for years, while others decide to modernize them at some point. In this article, you will learn what a legacy system is, how it can impact your business, and how a CIO should plan modernization to achieve real benefits.

Legacy system

  • A legacy software (legacy system) is one that the IT department cannot quickly repair or, if necessary, develop.
  • Using a legacy system can negatively impact a development team, business relationship, or even the software itself in the long run.

Legacy system

In the introduction, I mentioned that such systems may remain unchanged for years. There are various reasons for this: they may be issues related to the project, operational issues, or associated with compatibility problems or integration.

A legacy system often has a huge and long-lasting impact on the way many components in the organization work. This is due to the number of dependencies that can block development on many levels. Organizations can keep using such applications because they work “well enough,” or they don’t have good enough reasons to replace them. Often, there is simply no budget for replacing such a system with a modern solution.

However, the continued development of a legacy system may negatively affect the team, business relationships or even the software application itself in the long term. The decision to modernize and replace the legacy system with a newer solution should be made with full awareness of the potential threats and a predetermined plan.

Typical features of legacy systems

How do we know if we are dealing with a legacy system? There are several factors that need to be taken into account:

  • The age of the system – usually measured in years. The older the system, the larger the technological debt, and along with it, problems can arise on many levels of the project.
  • Limited development – when the length of the project is calculated in years, development becomes more difficult every year. In addition, if the organization does not maintain an adequate inventory of project functionality and documentation, there is a strong likelihood that with the increasing amount of code, a given project will become more difficult to understand, and thus the likelihood of errors will increase.
  • Rotation in the team – a team that has survived years of work together intact is really rare, especially in the IT market. Therefore, even if the team is relatively small, a large number of developers have probably worked on the product over the years. This rotation poses specific software development challenges to developers. After all, every programmer has his own idea of how to implement a given implementation. That is why – bearing in mind that there are, of course, appropriate templates and guidelines in the project, which developers should respect – despite all this, it is very difficult to be sure that the new code added by the developer will be developed in the same style as that of his predecessor over the years.
  • Tech debt and legacy technology – the IT world waits for no-one, and continues to develop every day. And so does technology. A legacy system developed over several years becomes increasingly distant from the latest technologies, making its components obsolete, functioning worse or causing shortcomings in important safety areas.
  • Uninteresting technology – older technology is less attractive to developers. To some extent, it hinders development in the profession. It can cause problems when trying to find an extra pair of hands to work on the project.

Why are legacy systems still in use in companies?

You may wonder why, despite the abovementioned disadvantages, many organizations still continue to use legacy systems. Most often, the reasons are as follows:

  • Business continuity – first and foremost, the legacy system ensures business continuity. The use of old technology that still works often outweighs the need to create something new.
  • The complexity of the project – replacing outdated technology in a long-running project is often a huge challenge, both in terms of business and project aspects, as well as those related to finances and human resources. To quote a popular saying in the IT world: “if it works, don’t touch it!”
  • Operational costs – an important aspect in favor of the continued use of a legacy system. Switching from one type of technology to another can generate large expenses. Often, the financial calculation shows that it is more profitable for the company to keep the older version of the application than to invest a lot of money in rewriting, data migration and the new infrastructure of the entire project. Therefore, companies are more likely to invest in completely new projects than to decide to rewrite existing ones.

A company deciding to modernize legacy systems will certainly face challenges such as:

  • Complexity – legacy systems are often written over a period of many years and are therefore complex and full of dependencies. All this makes it difficult to understand and manage such a system. The length of the code is not the only factor determining the complexity of the product. The legacy system usually consists of many business parts that are difficult to understand without spending a lot of time on it.
  • Integration and compatibility, i.e. “Integration Hell” – one of the main problems in the programming environment is the integration of environments, systems, applications or components. Rarely is the integration process easy and free of issues. Instead of spending relatively little time on it, programmers are forced to spend many hours or days improving these things.
  • Data migration – there is a high probability that something will go wrong when migrating data from the old system to a new one. Such a migration can be very time-consuming, so you should be prepared and plan everything as well as possible. This way, you can eliminate the potential risk of data loss.
  • Security issues – inadequate software security may be one of the main obstacles to modernization. Old protocols and authentication methods may differ significantly from newer security standards for systems and applications.
  • Budget – the cost of upgrading a legacy system can be huge and you should bear it in mind. In addition to the programming challenges, where spending starts as you invest in additional people in the team, and finishes with changing the programming environment, it may mean allocating additional resources – for example, when training employees in how to use a new system, replacing old equipment with new, or introducing changes in the working culture of the entire company (e.g., if you plan to implement Agile methods of work or DevOps culture).
  • Lack of competences and know-how – teams that have decided to replace their legacy system with a newer one may face the problem of lack of competences, experience or knowledge in the team. The initiative to modernize systems or applications must be led by people with expertise in business areas critical to the project and competences that will allow you to successfully replace the legacy application with newer technology.

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Agile Methodologies in Software Development

Find out what agile means and what are different agile methodologies in software development. Go to article!

Benefits of software modernization

The company can gain a great deal by modernizing and replacing such a long-developed system with new technology.

  • Better performance – an improvement in performance should be noticeable. Compared to outdated systems, the newer systems can manage much more traffic and processes, thanks to which the User Experience and application productivity are improved.
  • Improved scalability – the IT market is developing very quickly, which is why addressing demand for new functionalities of developed products is a very important challenge, and at the same time a big one. The challenge of replacing the legacy system with a newer solution, properly designed and based on good software development practices, should help when it comes to Agile product development and meeting the business needs that arise.
  • Safety – a change will also be visible in the area of safety and preventing security breaches. Legacy systems were likely designed before the discovery of many of today’s cybersecurity threats. This means that they are more vulnerable to these types of threats. Newer applications are developed in such a way that threats are taken into consideration at the stage of application development, e.g. with the use of DevSecOps (this approach, for example, is utilized in cloud native projects). Migrating from legacy systems to newer proven technologies can ensure that most of the previously detected threats are covered with appropriate security patches. Additional expenses for the safety of developed products can also be offset. When correctly implemented, the latest technologies reduce the risk of data theft, system hacking and damages.

Before you decide to modernize legacy software

Modernization of the legacy software application is a big challenge but at the same time it can be very beneficial to the product. Before starting modernization, it is worth organizing a meeting with a team of experienced employees and discussing all the important aspects of such an undertaking. It is worth consulting with:

  • an architect who will outline a vision of the new software,
  • a financial analyst who will present specific figures proving that modernizing the system, which the company would prefer “not to touch as long as it works”, will pay off,
  • Business Intelligence consultants who will give you tips on how to “get rid of Excel” and start using modern database systems and data analysis tools,
  • experienced programmers who will offer advice in the context of the latest technologies and competences,
  • a project manager who will keep an eye on the project throughout the modernization process.

When the decision to replace a legacy system is made, make sure that the roadmap is understandable to everyone, people know what their tasks are, defined goals are set, and it is clear what the potential benefits of such an upgrade are.

Should we keep using legacy software or consider modernization?

IT is one of the fastest growing markets in the world. Gartner predicts that by 2023, global IT spending will reach $4.6 trillion. This is an increase of 5% compared to the previous year.

Writing the best and latest software therefore plays a key role if you want to create the best quality products. With the rapid development of technology, the likelihood that products developed in-house can quickly become the definition of a legacy system is growing. This can negatively affect the development of the company as well as the entire business.

That’s why it is worth finding out when we should really think about creating something new, a system or an application, and in so doing deal with data migration and replacing older software with a new version. Here are some key aspects to look out for:

  1. The product is over 5 years old
    • Outdated software is one of the most common signals that modernization is necessary. A product which has been running for over 5 years probably already contains obsolete code. This leads, for example, to a lack of support for various plugins or dependencies, where components for older versions are no longer supported and developed. As a result, there are further problems with software performance, security and integration.
  2. No scalability
    • It is worth considering modernization of the system if the changing customer requirements are translating into an increasing number of software problems. Old software, developed over the years, probably no longer has the right attributes to meet the growing needs of users and allow for rapid and, most importantly, suitable product development.
  3. Rising costs
    • If you discover that maintaining older technology is becoming increasingly expensive, it’s probably time to consider upgrading it. Older software may require more costly hardware than modern solutions. Furthermore, the proper functioning of older systems often requires the assistance of specialists, which can generate additional costs and be very time-consuming.
  4. Lack of Support
    • As I mentioned earlier, an outdated product means you take the risk of not having support for the various software components in use. Vendors develop their plugins to a certain point, providing support for a specific version of the software. The lack of such support leads to security gaps, among other things. The time taken by programmers to create new functionalities is also much longer.
  5. Development is blocked
    • Everyone tries to maximize the potential of their product. However, when the existing software prevents the company from achieving its goals, it is another sign that you should consider modernization. Adapting to changing customer requirements and business conditions can be very difficult due to the fact that the product is defined as a legacy system. This can lead to barriers to the development of not only the product, but even the company as a whole.

Legacy system modernization strategies

There are proven practices that will allow you to maintain the usefulness and functionality of legacy systems. The most popular of these are:

  1. Replatforming and rehosting
    • The process of transferring legacy systems to a newer environment. This includes rebuilding the application or putting it on a new server. Such a change can improve product performance and reduce maintenance costs.
  2. Refactoring
    • Refactoring is about delving into the architecture of a product and trying to replace some of its components with another, often better, solution from the programming and business perspective. This includes, for example, restructuring the database, optimizing performance across multiple application levels, and improving security. Good refactoring, including whatever needs to be rewritten, is a real relief for developers. This is because fixing bugs or adding new functionalities for individual parts of the product can be much easier and less time-consuming in the future.
  3. Re-engineering
    • The most time-consuming and expensive procedure. It means starting everything from scratch using modern technologies to recreate the system and replace it. The aim of the reengineering should be, among other things, to improve the product architecture, performance, security and reduce application maintenance costs.
  4. Service Oriented Architecture (SOA)
    • Software development using the SOA approach involves segmenting large components into smaller, independent services accessible over a network. By dividing the code into smaller components and services, it is easier to develop it and solve possible errors.
  5. Application Program Interface (API)
    • A partial and helpful solution is to integrate the legacy system with APIs issued by other applications. Such integration can improve the scalability and performance of the software.
  6. Cloud
    • The cloud solution can be a positive impetus for improving integration and testing capabilities, as well as the quality of product service on many levels. The cloud also improves scalability and reduces operating costs. Let’s remember that despite the common misconception, the costs of a cloud solution do not have to be high, and the key is proper implementation (e.g., thanks to the use of DevOps processes). If you are set on a modern and reliable solution, moving the software to the cloud may be one of the best ways to achieve your goal.


Modernizing a legacy system is certainly a very difficult undertaking. It is not easy to give up on something that has been developed over the years, when the lines of code in the program can be measured in the thousands. In addition to figures, there is also the issue of business complexity, and thus all the processes and costs that need to be taken into account.

Remember that the decision to replace the legacy system or even partially modernize it may turn out to be a very good decision, but at the same time it may carry many hidden threats. If you have any doubts, it is worth utilizing the support of experienced specialists – correct calculation on many levels of the project is crucial in order to eliminate all problems and threats in advance.


Examples of legacy systems in organizations.

● Oracle, IBM, and Microsoft’s IT services software were at the top of Flexera’s ranking for products that are defined as legacy systems.
● Cloud infrastructure and outdated Walmart software.
● The NASA Orion spacecraft project.

What are the various types of legacy systems?

Mainframe systems – large, centralized computers called “mainframes” were used in the 1960s and 1970s. Many large organizations and government entities continue to use them.
● Client-Server system – compared to Mainframe systems, they are more scalable and flexible. They consist of a program running on the server and a client application running on the user’s device.
Desktop applications – traditional applications running on the user’s computer. They are often built on older programming languages such as C++ or Visual Basic.
Web applications – they run in a web browser. ASP and JSP are examples of technologies that are still used today in such applications.

What are some examples of legacy platforms?

IBM mainframes – the most popular legacy platform.
● Sun Solaris – most commonly used for web servers and other web applications in the 1990s.
Windows XP – Microsoft’s unsupported system, one of the most popular computer systems ever created.
AS/400 – used in IT sectors such as finance, healthcare and manufacturing; a highly valued platform in the 1990s.

At Inetum, Mateusz works as a Frontend Developer with several years of experience. His greatest passion is React technology. He develops a professional career in his spare time, creating applications in various technologies. Mateusz is also keen on reading books, especially fantasy ones, and is interested in cinema and creating unusual beverages.

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