Euristiq donates all profit to Ukraine
Company statement
read more


Legacy System Modernization: When and How to Do It Right

Andrii Shpak
February 6, 2023
10 mins to read

Table of Contents

    Well-established companies might realize they need to introduce digital innovations and improve their customer experience to be successful. What they might not realize yet is that in order to do so, their business has to go through a fundamental transformation and that includes considering legacy software modernization.

    Many organizations have their core operational functions run on outdated platforms with software that has aged long ago. And aged software isn’t a good thing, because the software doesn’t get better with time. Such companies run a high risk of losing operational efficiencies if something goes wrong, and it makes them unfit to innovate because meddling with a legacy system can take it down. That being said, it brings us to the first and the most important question – what is a legacy system, and how to recognize it?

    What is a legacy system?

    Legacy systems are outdated software programs that are still in use because they serve a critical business need. Their only advantage is that they keep the business running. They can no longer integrate with newer products and hinder organizational growth. Years of unresolved issues accumulate technical debt and the systems or applications become legacy.

    But not all legacy systems have necessarily been years in operation. Such systems are defined as a legacy because of their inability to correspond to the current business needs of an organization or to integrate with other systems. They can no longer be supported by the vendor, or the technology may become obsolete and it becomes hard to find a person who can maintain it. Thus maintenance becomes costly over time and any workarounds to achieve new desired functionality, do not work in the desired way.

    Combining innovation strategy with obsolete legacy systems ill-suited for scaling can pose a silent threat for businesses. Legacy software the company operates on may still be working, but it can block the company from innovating and beating the competition.

    how many companies have strategu for legacy modernization, Euristiq

    There is only one thing left to do, or in fact – there are two things left to do (let’s present it as a choice) – modernize or go home. By ‘go home’ we mean kill the legacy application and rewrite it from scratch. Either way, big changes are coming.

    Change is hard, especially if you are a traditional company with many years in business. According to surveys, 55% of companies without a digital transformation believe they have less than a year before they start to lose market share and 70% of companies either already have a digital transformation strategy in place or are working on one.

    As the business grows and develops, the system it is operating on needs to keep up. Legacy modernization will help implement new features faster, improve business performance and help with a customer acquisition strategy.

    In this article, we’ll go over some of the main reasons to modernize and explain what are the best ways to do it.

    4 reasons to modernize a legacy system

    The task of modernizing legacy software is an undertaking that the business might not see as a necessity. Why fix something that is not yet broken? The answer to this question lies in the hidden risks legacy system have – they are vulnerable, incompatible with new products or lack modern functionality. These can result in security breaches, inability to compete on the market and retain and attract new customers.

    Legacy software the company operates on may still be working, but it can block the company from innovating and beating the competition.

    It is a challenge in balancing between maintaining your legacy systems and being ready to scale your business according to customers’ needs. In case you wanted a little bit more coaxing into the ‘modernize your legacy system’ direction, we have listed here the most important reasons:

    Maintenance gets too expensive

    Approximately in just 5 years after the product release, legacy system maintenance can cost more than the original development budget. This mainly includes managing the old codes and raising the support tickets that can take days to solve the issue.

    Instead of introducing new services, you might find yourself in the constant business of fixing urgent issues that never stop occurring. Moreover, over time the number of specialists qualified to work with obsolete technologies will drastically diminish, and finding the specialists that can help you will get harder and more expensive.

    Lack of support or skills on the market

    Business owners might run into a situation where the vendor no longer supports their legacy system. It also means that no one is keeping the system compliant with current security requirements.

    With the custom-developed system, there might come a time when it is nearly impossible to find a person with the right skill set to carry out maintenance on obsolete technologies. And as young developers are constantly mastering new languages to brag about on their resumes, they are not willing to deal with someone’s legacy code. In contrast, up-to-date applications are much easier to support and it does not require costly training of dedicated staff.

    Impossible to add new features

    Adding new features is integral to business evolution and success. It helps to stay on top of the market and respond to customers’ expectations. Adding new features often requires connecting with a third-party tool or service and if the business operates on a legacy system that lacks compatibility, it might not work or work as intended.

    When it gets impossible to implement new features or a legacy software becomes incompatible with modern systems – it is a sure sign that it needs an upgrade. This will enable interaction with other systems and also improve system performance and its effectiveness drastically.

    Poor security

    One of the most important reasons why one should consider modernizing a legacy system is to achieve stronger security. What was acceptable in terms of security when the system was created, now might be a problem. Outdated systems cannot compete with the modern ones in terms of vulnerability to cyberattacks or data breaches.

    Compliance with process regulation standards is also an important factor to keep in mind. Not adhering to such software compliance standards as HIPAA, PCI, SOX, etc., may cost a company millions of dollars.

    All of the above-mentioned reasons are excellent excuses to finally move to a language or technology that is well-supported with development tools. The legacy transformation will enable your business to get the most value out of developing new products and launching new features.

    Methods for legacy application modernization

    All of the legacy modernization approaches fall into two main categories as to the strategy used in transformation. It can be either revolutionary or evolutionary depending on the number of structural changes that are imposed on a legacy system.

    Revolutionary method

    In the revolutionary method, the old system is completely substituted with the new one developed from scratch. It is done to avoid security breaches or complete and unexpected system shutdown. This method might be the case with older monolithic systems where one cannot modify a separate unit without modifying the whole system. For an application to be scalable it has to be modular or even better – redesigned with microservices-based architecture.

    There is, however, a downside to this strategy, as it involves risk and possible disruptions to the normal course of business. It can also be more expensive.

    Evolutionary method

    The evolutionary method is less painful as it does not require a system shutdown. It involves replacing one component at a time without disrupting the usual business processes. However, it can turn into a ‘band-aid method’ when one focuses on solving problems rather than removing the factors that cause them. This method is less risky but can be prolonged over time.

    Either transformation method you choose to follow will be crucial for securing your spot among top-performing companies on the market. It will enable bringing connected technology and IoT innovation to your business which 60% of executives believe will play an important role in their company’s digital strategy too.

    Legacy system modernization approaches

    Once you have decided which way in your legacy system modernization you would like to go, you can choose the approach based on the amount of impact it produces and complexity. The following approaches are ranked from the easiest and those with the lowest risk (evolutionary method) to those that have the greatest impact on the system and business processes (revolutionary method). Choosing the right option will help reduce the costs and improve your infrastructure.

    Legacy system modernization approaches, Euristiq


    Encapsulation is one of the most cost-efficient techniques and it’s also among the fastest. It reuses the main components of a legacy application encapsulating its data and functions and making it available via an API. Encapsulation simply provides a new interface to the current legacy system but does not solve maintenance issues. So it’s a good option if the legacy app has nicely written code, high business value, and still functions properly.


    Rehosting means redeploying the application to other physical, virtual, or cloud infrastructure without any code or functionality modification. This technique is also one of the most economical ones, is fast, has low risks and helps resolve support issues. It does not impose any negative impacts on the business and at the end of the process the system functions exactly the same.

    Although moving to cloud with rehosting technique does not make full use of cloud-native features, it still offers more reliable security and the ability to roll out constant updates. It also should be mentioned that rehosting is not the only way the legacy to cloud migration can be performed; it’s also possible with replatforming or refactoring. More about cloud migration strategy you can learn in the article.


    Replatforming allows migrating a legacy app or its components to a new platform with minimal changes to the code. It leaves the code structure and existing functionality intact. This option is perfect for those business owners who are worried that their customers will not adjust to the new system. The benefit of legacy cloud migration with replatforming technique is that it optimizes costs and offers base cloud functionality. This approach requires less effort than refactoring but can still offer basic cloud advantages.


    Refactoring technique optimizes the existing code without altering the legacy application’s behavior. Refactoring involves making changes to the backend elements to ensure smooth legacy migration to the cloud. It helps take full advantage of cloud-native features and move from containers to microservices. This approach is used to effectively reduce technical debt, improve performance, and make the system more flexible.


    Reachitecting is a more advanced approach to legacy system modernization which entails creating a new architecture and making changes to the code. It’s a fairly risky technique but it improves app functionality, allows to leverage better capabilities of the new tech stack and simplifies the process of implementing new features. Rearchitecting is also used to resolve performance and scalability issues.


    Rebuilding or redesigning is rewriting the legacy application’s code from scratch into a fully modernized, cloud native environment. This approach is used when the legacy app’s scope and specs are worth preserving. Rebuilding harnesses many technical advantages such as implementing DevOps, adopting technologies like microservices, containers, service meshes, etc. It is one of the longest methods and applies a lot of changes to the system which is deemed risky, but the benefits overweigh the risks. At the end of the rebuilding process, the business gains a more flexible system with better performance and lower operating costs.


    If all of the above-mentioned approaches are too expensive and won’t help achieve a desired outcome, then the legacy system is perhaps not worth saving. In this case it is better to retire the app and replace it altogether, creating a system that will serve the current business needs better. Replacing a system with a brand new, custom-built one, requires a significant amount of planning but in terms of completely corresponding to the new business needs it’s a sure winner.

    How to choose the right legacy modernization approach

    Now you may be wondering how to choose the right method for your digital transformation. Which one to select among these multiple options, what to consider?

    Well, the answer is simple – opt for the modernization approach which will bring the highest value to your business with minimum effort. You should consider the amount of transformation you would like your system to go through, and also take into account risks and cost. Jumping on the bandwagon and choosing the most popular option might not work well in your case, as all legacy systems are different.

    To simplify your legacy predicament, we advise concentrating on rearchitecting, rebuilding or replacing approaches, as these are the main options worth considering. Evaluate your system, prioritize what needs to be done according to the user research and start modernizing. And don’t forget that you can always consult tech experts such as ourselves to help you make the right choice and follow you through the whole modernization process.

    Checklist for legacy application modernization

    If by now you are feeling overwhelmed by the amount of choices you have to make in your legacy application modernization journey, don’t be. We have broken down the whole complex process into simple steps that will help you.

    1. Evaluate your legacy systems

    Start with thorough assessment of your legacy apps to define the current state and potential issues, taking into account your business growth plans. Carefully study and review the architecture, code, functionality and users’ pain points when interacting with the app, considering features that you would like to introduce in the future, assessing them from the technical perspective.

    Almost every modernization entails some level of disruption to the business and there are always risks of keeping the system as it is – security risks, risks with hidden maintenance costs. You need to weigh the pros and cons of each option to define whether modernization (and which technique) is worth the effort.

    2. Define success

    Do not embark on your legacy modernization journey without defining the measurable metrics of success. Define clear objectives so that the team would know what to focus on and what to leave out. Some of the good examples of such objectives look like this:

    Software performance is one of the most obvious metrics that should be tracked. It easily demonstrates how the modernization affected the functionality and can be a clear indication of successful transformation. That was the case with the legacy transformation project we’ve done for an airline, redesigning its website to 3X performance.

    3. Select the most viable approach

    Choose the modernization approach that will give you desired outcomes with the least efforts, and the fastest. Determine what parts of the current system you’d like to save and re-use if they offer a unique value, or consider ready-made solutions if they will cover that need for you for less cost. This could be the case, for example, with CRM systems – it might be cheaper to retire your current system if it’s outdated and does not serve the current need and adopt the existing solution.

    4. Choose the right technologies

    Once you’ve set your business and technical goals, you need to choose the right, future-ready tech stack to help you meet them. You might want to opt for cloud migration for speed, remote access, and scalability. Consider a microservices architecture if you currently have a monolithic application and would like to speed up your time-to-market, make your product scalable, improve security and introduce new features. You can also consider performance testing, redesigning the frontend, adopting event-driven design and many more.

    Selecting the right tech stack contributes to the efficiency of your legacy transformation, so you might want to consult tech experts to help you meet the right decisions.

    5. Plan staff training and system updates

    Here are a few more things to keep in mind to get the system up and running successfully. First of all, organize an extensive unit testing. Second of all, don’t forget to train your staff to use the new modernized application, if they will be the ones to use it. Make sure you have set the budget for it. And one more important thing is, plan for regular software updates to avoid possible issues in the future. If you omit doing so, soon you’ll have another outdated system on your hands.

    Our experience: Re-engineering airline’s legacy website

    Airline industry has a tight competition, a rich history, and many obsolete systems waiting to be modernized. One of our clients, Europe’s largest airline, recognized the need to rearchitect their legacy website, as it was slowing down business operations.

    The challenge

    The client called on Euristiq to provide a team of engineers who can modernize a legacy website, develop a new version to improve the performance and offer more value to customers. The main goal was to rearchitecture the legacy website to have faster business operations as buying tickets, booking accommodation, or renting cars.

    The approach

    The results

    Euristiq developed a new version of the website for Europe’s largest airline that has higher performance and improved interoperability. Due to cloud adoption, new architectural approach, interoperability improvement, and implementation of new UI/UX, the website’s organic traffic increased twofold. Services for buying tickets, booking accommodation, and renting cars are working smoothly on the new site which significantly impacts the company’s financial growth.


    Legacy systems are based on outdated technologies but are essential for business functionality. Their only advantage is that they keep the business running smoothly, without disruptions. Yet they fail to help to meet the market demands. In addition, they are often expensive and complicated to maintain. To implement changes within the business, legacy modernization has to be introduced to digitally transform the system into modern infrastructure.

    Our experts here at Euristiq can help you select the most appropriate transformation method to your business and redefine it with the latest IoT trends and technologies.

    Rate this article!

    5.00 out of 5, 4 ratings.
    Very good!