Best Practices

7 Legacy Application Modernization Approaches That Upgrade your app

Updated on
December 14, 2023
Table of content

Legacy application modernization is one of the headaches of product owners and CTOs. As legacy systems age, they become more dependable and expensive to update or scale. Issues with authentication, authorization, data security, data integrity, application integration, updates, and patches, you name it – all of the above happen to your legacy system with time.

The ten oldest federal government legacy systems that require legacy application modernization cost about $337 million annually to operate and maintain.

Legacy application modernization is the way business owners can save money and improve business operations. Finding the legacy application modernization solutions that suit your product is challenging. That's why in this article, I'll show you the following:

  • How to understand that it's time to modernize legacy applications?
  • What are the 7 best legacy application modernization strategies?
  • How to choose the modernization strategy for your project?

Plus, I'll share 3 application modernization cases we undertook at Uptech and the approaches we used. Let's dive in!

What is a Legacy System?

The first thing that comes to mind when we hear 'legacy system' is probably Apple Lisa and the code written in COBOL.

And you'd be right. That definitely would be a legacy application that needs modernization. But apart from that, any software/technology/system that is hard to maintain, support, and integrate with newer technologies is considered a legacy system.

But wait, if the legacy applications slow down the business, why do companies continue using them?

First, it can be cheaper than developing new solutions from scratch. Second, legacy systems often contain valuable data that cannot be ignored due to changing business requirements or factors outside your control (such as regulatory changes). Last but not least, writing a legacy system often lacks some requirements, which leads to the problem: the new solution may miss some important aspects of a product.

What is Legacy Application Modernization?

Legacy application modernization is the process of updating or replacing a legacy application (fully or partially) to include modern platform infrastructure, architecture, or features.

The main goal of legacy software modernization is to increase the system’s functionality, performance, and scalability. In business words, increase your profit and optimize the business processes.

Now, as we figured out what is legacy application and modernization, let’s move further and discover HOW to understand that your application needs modernization.

legacy application modernization

How To Understand That a Legacy Application Needs Modernization? 5 Red Flags

Red flags tell you that something is off in your daily routine as well as they may point out that your application needs updates. But how do you know when to modernize your legacy app? Let's see five red flags of legacy systems.

legacy application modernization

It takes many resources to maintain the app

The costs associated with maintaining and operating legacy systems are often significant. Even if you have an in-house team that manages your legacy application, you may still need to hire specialists to help during times of crisis or significant upgrades. This can be very expensive and time-consuming for you and your team members.

When a legacy app requires a large team of highly-skilled developers to keep it running, it leaves organizations with a difficult choice – either invest in app modernization or face ongoing problems.

It is hard to integrate new features into the app

Modern technologies integrate with each other seamlessly. Today, third-party software tools and services have built-in support for most programming languages and frameworks. For example, Uber uses the Google Maps API for customer navigation and journey visualization. Because these two technologies are pre-built and tested, there is no need to reinvent the wheel.

However, legacy applications may require a significant amount of custom code to integrate with APIs. Even if this is done, there's still the possibility that the final integration will not work as expected. Legacy application modernization solutions are required to overcome these kinds of challenges.

The app blocks your business growth

IMHO, that’s the main red flag. When a legacy system can no longer support your business, it can burden your team, and burdening the team will slow down the development. So when your legacy app affects business growth, it's time to consider legacy software modernization.

The app lacks security or compliance functionality

Because legacy systems are old, they may become less resistant to cyberattacks, harmful programs, and malware. In addition, vendors might stop supporting older versions of their software, meaning that no patches are provided, and no one keeps the system compliant with the latest security requirements. In this situation, organizations need to opt for legacy application modernization solutions.

The app damages users' experience

A vital element of user experience is the speed with which a business can respond to user needs. Can it introduce new technologies and features in weeks or months, or will it take years? Unfortunately, businesses bound to legacy systems lack organizational agility — the ability to adapt quickly to changing conditions.

Modernizing legacy applications is the next best step when legacy systems block innovations and damage user experience.

7 Key Application Modernization Approaches

Below, I gathered the 7 most common legacy system modernization approaches. Each of them serves a different purpose, and I gave some tips on when and what to use.  

legacy application modernization

#1 Encapsulate

Encapsulation is wrapping an existing application as an API within a new application or service. The existing app doesn't change, but it's made available as an API that other applications can consume.

Uptech tip: This approach is useful when you want to create a new application that uses some of your existing systems but don’t want to rewrite them.

#2 Rehost

Rehosting involves running your application on a different platform from where it was originally developed. This means moving from an on-premises system to the cloud or vice versa. While rehosting can be an effective strategy, it has its share of drawbacks, like high costs and downtime during migration.

#3 Replatform

Replatforming is similar to rehosting, but instead of moving your application to a new platform, it moves the entire stack of your application from one technology stack to another with minimal changes made in codebase or architecture.

Uptech tip: This approach is suitable for legacy applications that require changes in their underlying infrastructure, rewriting an entire microservice using container technology.

#4 Refactor

Refactoring is the process of making small incremental changes to code to improve its quality without altering its behavior. But before refactoring, we always run unit testing. It’s a must because the tests show if the behavior of the module is correct before and after the refactoring.

Check out the book by Martin Fowler, “Refactoring.” It’s a valuable piece of read.

Uptech tip: We often advise refactoring to reduce technical debt and improve code maintainability and extensibility.

#5 Rearchitect

A re-architecture is an intensive effort to redesign an existing application from scratch. The goal is to dramatically improve its performance and scalability compared to what was possible before re-architecting it.

#6 Rebuild

Unlike re-architect, where you only modify parts of the application, rebuild typically requires you to rewrite all components of the application from scratch.

When we rebuild the legacy system, we remove existing code and redesign the application, after which we add new functionality. It’s like software surgery. This can be seen as a last resort because it is expensive and time-consuming. However, it may also be the only way to build something new using modern technologies and practices that were unavailable when your legacy application was built.

Uptech tip: Rebuilding works best for the apps that are no longer supported by their vendors or if they have become too slow because of their codebase. It’s the priciest solution, yet the most reliable one.

#7 Repeat

​​If you want to avoid your software becoming a legacy system, you should audit your app systematically. It's a bitter truth we can't hide. At Uptech, we always take a fresh look at the app, change architectural approaches and add new tasks to the sprints if needed. And we do it regularly.

Application Modernization Uptech Cases

How we refactored the neobanking app

Recently, we finished our collaboration with a neobanking startup from the US – Cardless. It is a credit card company that provides sports fans with a credit card experience that's fairer, smoother, and more rewarding.

Challenge: Maintain the app on both OS

When we released the Android version, the client loved working with us, so they asked us to maintain the apps on both operating systems to meets their business needs.

Uptech solution

First, we reviewed the existing code for the iOS app and found some points to improve. We refactored the existing architecture and app logic to make the app work with no bugs and delays. As a result, iOS and Android app users received a much better user experience.

How we refactored the online delivery app

Sprent – an online delivery system enabling customers to buy anything from any store within their city. They came to us with existing Android & iOS apps and were looking for a partner to make the app more stable and implement some extra functionality.

legacy application modernization

Challenge: Make the existing app stable

When the client came to us, the app crash-free rate was only 85%. We had to fix crashes and make the app resilient before adding new features.

Uptech solution

Our engineering team took over the existing app, identified most of the bugs, and started refactoring. As a result, we reduced the crash-free ratio from 85% to 99+% in both Android and iOS apps.

legacy application modernization

Main Technologies for Legacy Application Modernization


Cloud technology has become a staple for modern businesses looking for cost-cutting measures and greater agility. This is especially true when it comes to modernizing legacy applications, as cloud computing offers the ability to run applications on scalable infrastructure that reduces the need for on-site servers and maintenance costs.

Cloud providers offer various services, including:

  • virtual machines;
  • storage;
  • networking.

All of them can be used to support legacy application modernization services.


The name 'microservices' speaks for itself. Simply put, it's a technology that divides applications into smaller pieces called microservices. These microservices are more agile and easier to manage than larger monolithic applications because they're easier to develop, deploy, test, and maintain.

Usually, to develop each microservice, you need a separate team or a vendor specializing in that functionality. When combined, these microservices form a complete application that is reused across multiple projects. It allows accommodating changes in requirements over time.


Legacy systems modernization powers up your business and becomes very beneficial in the long-term perspective. By modernizing your legacy software, you update the product so it offers better functionality, becomes more efficient, and maximizes the user experience. As a result, your company can operate with the technology that fits its business needs today.

In addition, modernized systems are also more secure from malicious attacks, such as hacking attempts or viruses. By replacing outdated legacy systems with current technology, you better automate processes, generate more revenue and efficiently use the technology investment.

I hope this article highlighted the importance of legacy systems modernization and you found the strategy that suits your needs. But if you're hesitating between the modernization strategies or need help transitioning legacy systems, feel free to reach out.