Legacy Application Modernization: Best Practices, Strategies & Approaches for 2025

As a CTO with over 14 years of experience, I know how much of a headache legacy applications can be for business owners:

• The application can’t handle peak loads, and there is no way to fix it 
• Adding new features becomes more costly than before 
• Bugs appear in unexpected parts of the application, often after fixing other bugs 
• It can be hard to find developers to work with outdated technologies 

However, I can assure you that these challenges don’t have to hold you back from business growth. In this guide, I’ll share the most effective legacy application modernization approaches, highlight the key components of modernization strategies, and explain what the legacy app modernization process might look like in practice based on MobiDev clients’ success stories. 

What Is A Legacy Application?

A legacy application is one that may be based on outdated technologies but is critical for day-to-day operations. In other words, a legacy app is a long-living project with complex entangled code, outdated technologies, or poor architecture. Moreover, it can combine all these characteristics. Such an application can’t meet the company’s current business needs and requires modernization or full replacement. 

However, the comprehensive definition of a legacy application goes beyond the simplistic conception of old software, as the age of the product isn’t the key criterion here. In fact, any application can be considered a legacy if it’s reached a point where it is slowing down or otherwise impacting the ability of an organization to expand, adapt, or transform as it needs to. 

This functional definition is more helpful when assessing your enterprise’s applications. A system implemented a decade ago may not be a problem area if it still perfectly meets the needs it was created for. On the other hand, an application built only a couple of years ago may unexpectedly block your business’ ability to react to a change in the industry or market, creating a threat to its growth and viability.

How Do Legacy Applications Negatively Impact Businesses?

Legacy applications have a range of features that call into question the quality of the business product. Here are some of the problems you can face while working with legacy apps that can negatively impact the business:

• Difficulties of product maintenance. Technologies used in the project get out of date with time. This can result in difficulty with app service and maintenance; it requires timely updates and replacing the unsupported tools with new ones. This also includes bugs and different approaches to coding that might be used, making the code a puzzle.
• Limited scalability. Legacy apps are often unable to scale to meet changing business needs and growth demands. 
• Insufficient level of security. Legacy products can be vulnerable to cyberattacks because of outdated technologies or just the lack of attention to this aspect in the development stage. 
• Incompatibility. Some legacy apps can be incompatible with new technologies and software which can lead to issues when there is a need to integrate it with other systems. 
• Difficulties with adding new features. Legacy applications can be difficult to modify to add new features because of their complex structure and dependencies.
• High service costs. Legacy apps can be costly when it comes to supporting them; mainly because you need specialists that can work with outdated technologies. 

Why Do Applications Become Legacy Products?

In most cases, this happens due to several reasons:

• Requirements uncertainty. Sometimes, product owners have a rough idea of what features they want to have in a product, but the requirements change during the process of app development. As you start to work with new requirements, the application architecture should be changed as well. 
• Programming languages, libraries, and platforms change significantly every few years. So you always need to move to the newest versions and use relevant tools. 
• Evolving business needs. When creating a new product you cannot always anticipate all the features that will be necessary at the beginning of the project. But once you release it, receive customer reviews, and navigate shifting regulatory landscapes, major alterations may be required.

It’s also important to clean the code in a timely manner; otherwise, it becomes too complex for understanding and maintenance. As a result, this leads to the above-mentioned problems. 

8 Tips to Avoid Legacy Code in Apps  

1. Adopt a code style and follow it 
2. Practice regular refactoring and updating of old, outdated code 
3. Implement code coverage with autotests to quickly detect problems and errors 
4. Adopt continuous integration to minimize garbage while team members work on different tasks
5. Practice code review to decrease the amount of cumbersome code
6. Involve static analysis tools to detect issues and code quality automatically
7. Keep product architecture in an updated state, and adjust it to fit new requirements
8. Update project documentation consistently according to product growth

Legacy Application Modernization Strategies

If a legacy application is unable to meet the business needs of the modern competitive landscape, it should be modernized. There are two main legacy application modernization strategies that differ fundamentally from one another:

1. Evolutionary strategy — slowly and gradually improving the architecture of the application and code quality
2. Revolutionary strategy — completely rewriting the code or allocating time for primary refactoring.
   

Which strategy you choose depends on the project requirements, the business needs you are going to meet and the resources and time you can spend on your legacy application modernization process.

Top 8 Legacy Application Modernization Approaches

When your app’s relevance becomes a problem, your initial priority should be to define a comprehensive legacy app modernization strategy, which entails mapping out a high-level plan and roadmap for the modernization effort. 

Let’s take a brief look at some legacy app modernization approaches, and then dive deeper into their details. 

1. Application Rehosting

   This is the process of moving an application from one hosting environment to another. Rehosting is a popular approach among large enterprises as it allows them to improve system performance without disrupting existing workflows.

2. Application Replatforming

   This can help minimize scalability limitations, improve security issues, and advance compatibility with new technologies. However, migration to a new platform can be a costly and complex challenge.

3. Application Reengineering

   Reengineering is a review of processes and systems to improve application efficiency and performance. It can be used to enhance the functionality of a legacy app and increase its scalability.

4. Application Refactoring
   Refactoring means changing the structure of the application to improve its readability and ease of maintenance. It can be used for improving compatibility and adding new features to a legacy app.
5. Application Rearchitecting  

   Rearchitecting is a common modernization approach for complex, business-critical legacy applications where simply refactoring or rehosting is insufficient to meet evolving requirements. In this case, you need to make significant architectural changes to the core structure and design of the product.

6. Reutilizing or Encapsulation
   Encapsulation is a technique for reutilizing legacy app components by wrapping it into a new technology, for example, using Docker containers. This approach is low-cost and will allow the launching of the product on a new platform and integration with modern API.

7. Application Retirement
   Also known as application decommissioning, it involves shutting down obsolete business applications while retaining access to older data. This process may limit some tasks but results in significant cost savings and optimized resources.
8. Application Rebuilding

   This approach means completely rebuilding the application from scratch while maintaining its original scope and specifications.

Each legacy app should be thoroughly analyzed to understand which tools should be used for its modernization. It’s necessary to take into account the following factors: 

• the code quality 
• timeframes and budget 
• the condition of libraries and frameworks used in the project 

Why Start Legacy Application Modernization with Audit

A technical audit is a crucial step in the legacy app modernization process to understand what changes are necessary and what the modernization risks are. The key principle is simple: before solving the problem, we need to identify its origin. A tech audit helps to recognize tech debt in the code and architecture of the application and its nature. The risks of using the product are determined as well.  

Also, tech audits help to define which parts of the application can be migrated to a new platform, and which parts need to be reworked. As a result of a legacy app tech audit, you can get a list of recommendations for improving the code and architecture, along with a clearer project budget and timeline.

You need a tech audit if you are thinking about: 

• Adding new features 
• Making your product fall within operational industry standards and norms 
• Developing the competitive advantage of your business 
• Identifying areas of your application that require updating or replacement 
• Better detection and fixing of errors 
• Increasing performance 

The process of a technical audit can be challenging in some cases. For example, having relevant documentation helps to understand the product much faster than if it’s outdated. Also, big monolithic apps are hard to understand as such products can be confusing and difficult. To overcome these challenges, I recommend that you work with experienced software engineers and consultants.

Helping businesses build, scale, and modernize software products since 2009, MobiDev has an established technical audit workflow proven by our clients’ success. If you’re not sure where to start your legacy application modernization journey, feel free to reach out and discuss your business challenges with my colleagues. 

Top 5 Popular Legacy Application Modernization Techniques

Now let’s move on to how exactly apps can be modernized. In this part of the article, we’ll take a detailed look at the most popular legacy modernization techniques and see what business challenges they can solve. 

1. App Migration to The Cloud

Application migration to the cloud is the process of moving a software application from an on-premises server to a remote cloud provider’s environment to improve the availability and scalability of the application. In the cloud, you can store and process data, run applications, and do a lot of other things without buying and supporting your own infrastructure. 

Application migration to the cloud has the following advantages:

• Improving application availability: the cloud allows for running applications on remote servers that provide high availability and reduce downtime.
• Increasing scalability: the cloud environment allows you to easily scale up to provide high performance and work efficiency. 
• Reducing service costs: the cloud helps to reduce costs for infrastructure maintenance as you always can use remote servers and don’t need to buy equipment. 
• Easy application updating: you can update your applications in a centralized way, without the necessity to install updates on each server. 
• Improved security: the cloud infrastructure provides a higher level of security than local servers and allows you to control access to the applications and data easily. 

However, migration to the cloud isn’t an all-in-one solution for all legacy apps. Each legacy application requires a unique approach to cloud modernization services depending on many factors. 

2. Moving App from Monolith to Microservices

Application modernization with microservices is a process where the application is split into small logic-separated services, which work in a mutual ecosystem. Migrating to microservices is helpful when the monolith application is too big and too complex and its maintenance and development become a very complicated task. In cases when the application requirements change very often and it is necessary to implement new features quickly, a transition to microservices can accelerate the development process and make adding new features simpler and faster. 

Moving to microservices has the following benefits:

• Improved performance: microservices help to scale specific components of the system when it’s necessary. With microservices, there is no need to scale the application as a whole. 
• Better fault tolerance: if there is an error in one service, the rest of the services continue to function, which allows for keeping the whole system working effectively. 
• More convenient development: splitting the application into separate services allows the development team to build and test them independently from each other, so the development process will be faster and more efficient.
• Fast change delivery: each service can be evolved separately, which allows for delivering changes really quickly within the services, without the necessity to re-release the whole system.

In general, moving from monolith to microservices can significantly improve the flexibility and scalability of the application, helping businesses to grow and develop faster and meet customer needs more effectively.

3. Legacy App Tech Stack Modernization

Rebuilding an application in a new form can decrease costs, improve quality and customer service, and accelerate delivery speed. The main purpose of modernizing the tech stack is to improve the product’s performance and efficiency. 

We can migrate legacy systems to a reliable tech stack, taking into consideration the characteristics of legacy projects. Here are the most common scenarios.

However, these are only recommendations, as each project is unique and requires unique solutions. Therefore, it’s always a better option to start with a technical audit to find the most effective strategy for legacy application modernization. 

4. Migrating Desktop Legacy App to Web

Another technique of legacy application migration is moving applications from local computers to web servers to offer users access to them via a browser. This approach is usually used in organizations where employees work from different places and need access to the applications regardless of their location. 

Migrating desktop applications to the web has the following benefits:

1. Reducing service costs: migrating desktop applications to the web helps to minimize the costs associated with user computer service, as all applications are on the web server. 
2. Increasing mobility: employees have an opportunity to work remotely and have access to applications from every location in the world. 
3. Easy application updates: you can update your applications in a centralized way, without the necessity to install updates on each computer. 
4. Increasing security: using web applications allows you to control access to applications and protects against hackers and viruses. 
5. Better flexibility: migrating desktop applications to the web allows you to create new applications and features that can be used on every device where there is a browser; it’s also easier to adapt the applications for mobile devices. This can significantly expand the list of platforms where your product is available. 

Migrating desktop applications to the web is an important step in business growth that helps to increase employee performance and increase business mobility. 

5. Wrapping a Legacy Application into a Modern Technology

Another approach to software modernization is covering a legacy application with modern technology, for example, Docker or REST. Encapsulation is a technique for reutilizing legacy app components. While leaving the code in its current environment, encapsulation links it to the new presentation and accesses layers via an API. This technique helps to leverage the application and enrich its features and value. At MobiDev, we use this technique to provide low-cost and low-risk legacy app modernization to meet your demands.

Legacy App Modernization Success Story: ERP & POS System for Retail

In 2013, Comcash CEO Richard Stack committed MobiDev to completely revamping his POS solution. Comcash entered the market in 1996 as a local POS system targeted at the US retail market. Richard had a plan to scale up Comcash by transforming it into a more robust and innovative product to better serve his clients.

Project goal:

Transform Comcash from an on-premises to a cloud-based ERP system consisting of point of sale (POS), inventory management, e-commerce, and accounting systems for multi-channel, multi-location retailers.

Modernization approach:

By starting with a comprehensive tech consulting stage, we crafted detailed project documentation. This helped us clarify requirements, mitigate risks, and prioritize scope for the initial version. To meet the requirements, we rebuilt the platform using relevant technologies. This approach allowed us to overcome the limitations of the old product and gradually replace it with the new cloud-based ERP solution without disrupting operations.

Cooperation model: Dedicated development team of 6-8 experts

The key deliverables:

• Completed the first version of Comcash within the deadline of 1 year
• Implemented automated testing and server deployment to ensure 24/7 reliability
• Enabled data science-based functionality to predict and facilitate sales

Achievements:

• Today, Comcash boasts a presence in over 3,000 locations, reflecting its increasing popularity in the market.
• In October 2022, Comcash was acquired by POS Nation, a leading provider of point-of-sale systems. 
• Since 2013, MobiDev has provided comprehensive support for the entire development process of the Comcash system. This has ensured the platform’s ongoing deployment and evolution to meet the evolving needs of its growing customer base.

[Together with MobiDev], we’re able to work on a 24-hour development cycle, and we release software repeatedly faster than any of our competitors — and there is no overtime. We could never create what we have with MobiDev in my office in California. The tech market is just too competitive these days. If you are interested in developing a world-class product and working with a great group of friendly co-workers every day, I wholeheartedly recommend MobiDev.

Richard Stack

CEO of Comcash Inc.

How to Modernize Legacy Applications: MobiDev’s Approach

Once you decide to modernize your legacy application, the process will include the following main stages:

1. Analyzing the Current Legacy App

We begin with an in-depth interview to identify the problems from the client’s perspective. This initial assessment helps us focus our analysis effectively. During the software audit, we assess key areas, including architecture quality, documentation quality, code quality, effectiveness of tools in use, and potential security risks.

2. Aligning Business Objectives with Tech Strategy

Next, at the tech strategy creation stage, we set the modernization goals, taking into account the product’s unique features and limitations. This involves focusing on functionality, performance, scalability, security, compatibility with other systems, and establishing key metrics for performance, code quality, and reliability.

3. Choosing the Legacy App Modernization Approach

At this stage, we evaluate the product’s limitations and develop a detailed modernization plan. This plan outlines the steps, timeline, required resources, and identifies potential risks along with strategies for mitigation.

4. Implementing Legacy App Modernization

It’s crucial to have a well-coordinated team of seasoned app modernization specialists to bring their expertise to the project. At MobiDev, we assign a dedicated development team led by a project manager to ensure transparent and effective budget and resource management. During the testing phase, we verify the accuracy and effectiveness of each enhancement, implementing the changes into the environment.

5. Adoption and Maintenance

After modernization is complete, we create a plan for adoption and maintenance to ensure a smooth integration with minimal disruption. Our team maintains open communication to support continuous improvements aligned with evolving business goals.

Feel free to contact us if you need legacy application modernization services to help your business grow. We are always ready to assist you in achieving your business goals by providing software consulting & engineering services.