Legacy App Modernization Roadmap - a Step-by-Step Guide

First published on
June 16, 2023
Last updated on
June 16, 2023


7 Approaches to Legacy System Modernization

Let's start by discussing the most popular approaches to legacy system modernization. The choice of each depends on the individual situation and business needs, so you can consult with a company that specializes in legacy app modernization before making a decision.


The Retain/Encapsulate approach in legacy system modernization involves preserving the existing application while encapsulating it within a modernized layer. It aims to isolate the legacy system from the rest of the architecture, allowing it to continue functioning without hindering the adoption of new technologies or business processes. 


Rehosting involves moving the legacy system to a new hardware or software environment without making significant changes to the underlying code. It can include migrating to the cloud or virtualized infrastructure to improve performance and scalability. This solution reduces the cost of maintenance and increases system efficiency. 


Replatforming entails moving the legacy system to a new platform or technology stack, often with some modifications to ensure compatibility. It aims to leverage the benefits of the new platform while minimizing the need for extensive code changes.


Refactoring involves making improvements to the existing codebase, such as restructuring the database or rewriting parts of the system, without changing its overall functionality. It focuses on enhancing code quality, maintainability, and extensibility. Such a process makes it much easier to fix bugs and add new features in the future.


This approach to legacy system modernization is about redesigning the system's architecture to address limitations and align it with modern principles and practices. It may require significant changes to the system's structure and components. Rearchitecting provides an opportunity to align the legacy system with current technological trends and enables easier integration with other tools and services; however, it requires careful planning and skilled architectural expertise.


The rebuild approach in legacy application modernization involves completely rewriting the existing application from scratch while aiming to replicate its functionality. It entails discarding the legacy codebase and starting fresh with the newest solutions available. It allows for a clean slate, addressing the limitations and constraints of the legacy system while maintaining the functionality of the existing infrastructure.


In some cases, replacing the legacy system with a completely new off-the-shelf solution or custom-built software may be the most viable option. This approach offers an opportunity to redesign the system from scratch, implement whole new functionality, and leverage modern technologies, architectures, and development practices. This option is usually the most cost and time-consuming as it requires careful planning, data migration, and comprehensive testing to ensure a smooth transition.

Main technologies for application modernization


Cloud computing involves using remote servers hosted on the internet to store, manage, and process data instead of relying solely on local infrastructure. In the context of legacy app modernization strategy, this solution provides greater scalability, flexibility, and cost optimization by leveraging on-demand resources, auto-scaling, and pay-as-you-go pricing models. Cloud computing enables organizations to modernize legacy applications by:

  • optimizing infrastructure costs,
  • increasing scalability,
  • simplifying management and maintenance.


Containers, such as Docker and Kubernetes, are lightweight, isolated environments that package applications and their dependencies, allowing them to run consistently across different computing environments. Containers provide portability and flexibility, making it easier to modernize the system. Legacy applications can be containerized, allowing for improved deployment, scalability, and management. 


Microservices architecture involves breaking down a monolithic application into smaller, independent services that communicate with each other through APIs. This approach enables legacy app modernization by transforming the application into a collection of modular services. Each microservice can be developed, deployed, and scaled independently, promoting agility and flexibility. Microservices allow organizations to update and enhance specific components without disrupting the entire system which makes it easier and faster to update.

By combining cloud computing, containers, and microservices, organizations can modernize their legacy applications to meet the demands of today's digital landscape. These technologies provide the necessary infrastructure, deployment mechanisms, and architectural approaches to enable fast and smooth business growth.

Why do you need a legacy app modernization strategy?

Legacy system modernization is a big deal and such an operation cannot be left to chance. In this case, solid preparation and planning of the application modernization roadmap are as important as the process itself. Does the strategy require your time and commitment? Yes, it does, but certainly less than the subsequent remediation of errors associated with poorly executed rebuilding or restructuring. 

A legacy app modernization strategy will help you:

  • Identify your business goals and needs.
  • Assess your organization's resources and decide in which areas you need development or consulting support.
  • Estimate the time and cost required for upgrades.
  • Identify the most important functionalities of the system.
  • Reduce bottlenecks and slowdowns.
  • Prepare a long-term growth strategy based on new opportunities.
  • Prepare for potential difficulties and reduce the risk of error.
  • Carry out the process faster and more efficiently.

Legacy app modernization roadmap - a step-by-step guide

Step 1: Evaluate your legacy system

Any change strategy should start with an understanding and assessment of the baseline. Analyze your legacy app. Consider its nature, workflow, advantages, key functionalities, and aspects that you are comfortable with and that you would like to keep or replicate in the new app. Identify how the current system is related to the others and how changing it will affect other tools and applications your company uses. 

Consider that you and your team are used to the current solution and have your own ways to deal with its limitations. To get a broader perspective and more objective insight, you can have your legacy app audited by a company that specializes in systems modernization.

Step 2: Define the problems

A key part of a rebuild and upgrade strategy is to identify problem areas and pinpoint specific situations where the system is not working as it should. Maybe the case is internal workflow, or maybe the capacity of the system during periods of increased traffic. Maybe the application is keeping you from adding new integrations, or maybe you're concerned about security. Every industry has its own characteristics and requires different solutions, so the more accurately you identify your problems, the more apt you will be to solve them in your new system.

Step 3: Create a unified product vision

The possibilities for digital product development today are almost endless, and the scope for customization allows you to get a tailor-made solution. Create a clear, unified product vision: what the application should look like, what it should do, its place in your overall growth strategy, and which functionalities are key and convenient for you. This will help the development team offer you a product best suited to your company's needs.

Step 4: Establish priorities, needs and goals

After describing the problems and limitations, it's time for the much more enjoyable part - the future! The main purpose of legacy app modernization is to enable you to achieve goals that were not previously within your reach, so at this stage of the strategy, identify your company's business and technological needs. Improved UX, cost-efficiency, better performance, greater scalability, lower maintenance costs, expandability, and integration – these are just a few of the goals you can achieve with modernization. 

It's crucial at this stage to decide what your priorities are. You can use a needs matrix to assess the goals that will give you the greatest benefit with the least effort and start there.

Step 5: Choose the application modernization approach

At this stage of your legacy app modernization roadmap you already have a clear understanding of the challenges and limitations of your current system and the needs you want to achieve, so it will be easier for you to choose the right upgrade approach we discussed earlier. If you have a limited budget and your app requires relatively few changes to function better, opt for a less radical upgrade, such as Retaining/Encapsulation, Rehosting, or Replatforming. If you need a major overhaul of the infrastructure or to design the entire system from scratch, consider Refactoring, Rearchitection, Rebuilding, or Replacement.

Step 6: Set a timeline

A strategy without a timeline is just a bunch of ideas, so carefully plan the timeline of your legacy app modernization. Take into account your company's development plans in the short and long term. Modernization is better done during a quiet period, so if you're in the middle of a major project, it's better to wait until it's completed. On the other hand, if you are planning to expand or develop, such as starting to sell in a new market, merge with another company or expand your staff, it is better to carry out the modernization earlier. That way, your company will be ready for new challenges and more traffic, and new employees will learn right away a system that will stay with them for a long time instead of a legacy system that will change in a moment.

When planning the timeline, also leave a margin for possible delays – in an agile development process, many ideas and modifications can be made during the process, so you'd better not be constrained by too rigid a schedule.

Step 7: Write a risk management plan

A well-planned strategy allows you to minimize the risk of mistakes, but as they say – expect the unexpected. In any business operation, something can go wrong, and the point is not to hope that problems don't happen but to be ready when they do. Good practice in preparing a risk management plan is the "What if..." method. Write down as many potential problems you may encounter as possible. Don't limit yourself! The more black scenarios you work through at this stage, the easier it will be to implement disaster recovery if any of them become a reality.

Step 8: Establish KPIs

How will you know that legacy app modernization has delivered the expected results? It's easy - thanks to KPIs. Set specific and (if possible) measurable indicators of a satisfactory system upgrade. These could be page load speed, quality of performance, system capacity during periods of increased traffic, number of operations processed or any other software performance metric.

Step 9: Choose the right modernization partner

Legacy system upgrading is a huge step and demanding process, and although the results are worth it, at first it may seem challenging. Fortunately, you don't have to carry it out alone. Few companies have enough resources within their structures to carry out legacy app modernization in-house, so the final but fundamental step in the strategy is to choose the right modernization partner. 

Software houses specializing in custom software development, product design, consulting, and cloud solutions will guide you through the entire process from planning to implementation. Experienced companies have access to the latest technologies and development practices, as well as knowledge gained from previous implementations, so they will be a great support. When choosing a business partner, pay attention to the scope of services, portfolio, and ratings in platforms such as Clutch, or other trusted ratings like:

Next steps

In the world of modern business, digital products are the cornerstone of operations and growth, but to keep it that way, software capabilities must keep pace with a company's ambitions. And even surpass them. Legacy app modernization allows you to improve performance, optimize user experience, save time and money, increase scalability, flexibility, and security, and strengthen your market position. Few investments can be said to be sure to pay off. Legacy system modernization is one of them. 

If you need technical support with an upgrade or rebuild of your software, contact us! 

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