Legacy Application Modernization: A Step-by-Step Guide

In an endlessly evolving tech landscape, all companies eventually feel the strain of outdated legacy software. Legacy application modernization is often necessary when it comes to creating a modern, agile technology infrastructure that spurs business growth.

This blog article details steps and best practices, outline key legacy system modernization approaches, and explore the benefits of conducting a modernization project. Additionally, we will explain the critical importance of updating outdated systems, the challenges companies often face, and ways that BD Emerson’s experienced Technology Team can help.  

What is Legacy Software Modernization?

Legacy system modernization is the process of updating outdated business technology, which can include legacy apps, infrastructure, databases, and processes, to create scalable and secure technology systems that fulfill modern digital needs. The modernization of legacy applications is often a key consideration of digital transformation initiatives.  

Outdated legacy systems can create what is called process debt, which is the accumulation of redundancies and inefficiencies in workflows over time. Digital transformation projects target these inefficiencies, which can cost businesses both money and time and lead to devastating incidents, like security breaches.

BD Emerson’s Digital Transformation experts teach organizations how to modernize legacy applications without disrupting business operations.  

Learn more about BD Emerson’s Digital Transformation Services

Legacy Modernization Best Practices: A Step-by-Step Guide

Legacy modernization trends over the last two decades have surfaced some essential best practices for modernization strategies:

1) Perform a thorough assessment of your legacy systems

Before you jump into modernizing legacy applications, you need a clear picture of the current state of your systems. This step can often include:  

• Compiling a list of all applications and systems

• Recording details about your technology stack and the versions of its applications

• Accurately measuring your system’s performance and resilience

• Reviewing spending on licensing, maintenance, infrastructure, and so on.

• Understanding dependencies between applications and workflows

• Analyzing security and compliance by looking for gaps and tracking pertinent regulatory obligations and requirements

• Collecting insights and feedback from employees and customers on various aspects of system performance and difficulties

A comprehensive assessment is essential when it comes to completing the following steps of legacy modernization.

2) Establish a clear vision and goals for the modernization project

Successful modernization is about more than updating technology. It should support your desired business outcomes. This step includes:  

• Mapping business objectives to modernization initiatives

• Defining clear metrics to measure success

• Prioritizing legacy system transformation by business impact  

• Mapping goals to technology and security gaps

• Getting buy-in and support from business leaders, IT and engineering teams, and customers

At the heart of effective digital transformation efforts is aligning technology with business goals, and legacy system modernization is no different.

3) Build a modernization roadmap with phases, costs, and timelines

The most successful modernization programs are phased, realistic, and designed to minimize disruption while delivering incremental business value. A strong roadmap should:

• Break modernization into manageable phases or workstreams

• Identify quick wins versus longer-term transformations

• Estimate costs across development, licensing, infrastructure, security, and training

• Define realistic timelines with clear milestones and dependencies

• Account for operational risk, downtime windows, and change management

This roadmap becomes the shared source of truth that aligns executives, IT, security, and engineering teams, while keeping scope creep and budget overruns at bay.

4) Focus on data accuracy and integration

Data is often the most fragile and business-critical component of legacy environments. Poor data quality or broken integrations can derail even the best modernization plans.  

Prioritize:

• Cleansing, normalizing, and validating legacy data before migration

• Mapping data flows across applications, APIs, and third-party systems

• Ensuring real-time or near-real-time integrations where business operations depend on them

• Establishing strong data governance, access controls, and auditability

• Addressing privacy, retention, and regulatory requirements early

Modern platforms amplify both the value and the risk of data, ensuring that accuracy, consistency, and integration are foundational.  

5) Carefully select your technology stack and partners

Modernization decisions can lock your organization into platforms and vendors for years. Choosing the right technologies and partners requires balancing innovation with stability and security. Best practices include:

• Selecting cloud, platform, and tooling options that align with long-term business strategy

• Avoiding unnecessary complexity or vendor lock-in

• Evaluating security, compliance, and scalability capabilities upfront

• Ensuring compatibility with existing systems that won’t be modernized immediately

• Partnering with experienced modernization providers, like BD Emerson who understand both technology and regulatory risk

The right partners bring hard-earned lessons, proven frameworks, and the ability to anticipate pitfalls before they become costly problems.

6) Execute legacy modernization techniques in phases

There’s no one-size-fits-all approach to modernization. Most organizations use a combination of techniques depending on system criticality, risk tolerance, and business urgency. These may include:

• Rehosting (lift-and-shift) to reduce infrastructure risk quickly

• Refactoring or re-architecting applications for cloud-native performance

• Replatforming to modern runtimes or managed services

• Replacing legacy systems with modern SaaS solutions

• Retiring applications that no longer deliver business value

Executing these techniques in phases reduces operational risk, allows teams to learn and adapt, and ensures continuity for customers and employees. These techniques will be explained in greater depth in the next section.

7) Conduct testing, monitor performance, and continuously improve

Modernization doesn’t end at deployment. Ongoing testing and optimization are essential to realizing long-term value. This step should include:

• Comprehensive functional, performance, and security testing

• Monitoring system availability, latency, and user experience

• Tracking modernization KPIs against the original business goals

• Identifying new optimization opportunities as workloads evolve

• Continuously improving security posture and compliance alignment

Organizations that treat legacy modernization as an ongoing capability, not a one-time project, are best positioned to scale, adapt, and compete in an increasingly digital and regulated environment.

Key Approaches to Legacy App Modernization

The legacy software modernization process looks different for every company, depending on existing systems, resources, technical debt, and leadership buy-in. BD Emerson’s Technology Team provides a thorough assessment at the start of each company’s application modernization journey, to ensure that the modernization effort only improves core business operations and results in cost savings. Our team helps you determine which key modernization techniques work for your systems, if not a hybrid approach that combines multiple.  

1. Rehosting (Migration) - Rehosting often means migrating legacy applications, without changing code, from on-premise servers to a new environment, like the cloud. This is often the best option for a quick solution to infrastructure and scalability concerns.  

2. Replatforming – For systems that are not too complex, replatforming is a viable solution where technologies are migrated to a new environment and can include minimal code changes and adjustments for improved capabilities.  

3. Refactoring – When applications lag in performance, refactoring is an approach that restructures and optimizes existing code to improve performance. Refactoring can ensure the app’s maintainability, testability, and performance, but does not change the app’s external behavior.

4. Rearchitecting – Rearchitecting requires a more invasive approach, including the redesign of the system’s existing architecture in order to adapt to modern technologies and software design patterns. Because of its comprehensive nature, rearchitecting is often carried out through a phased approach to manage the process and address any issues. This approach, while effort-intensive, can significantly improve the app’s scalability, efficiency, and agility.

5. Full Replacement/Rebuild -- This legacy modernization approach is usually undertaken only when legacy systems are too outdated and unreliable in the face of evolving security risks. It entails the complete replacement of the legacy software and systems, offering the greatest flexibility and potential for innovation. However, this option is also the most expensive and can stall at unforeseen issues.

Legacy Modernization Benefits

The benefits of legacy application modernization extend far beyond the perks of integrating updated software. When executed strategically, legacy modernization initiatives create measurable business value across performance, security, cost, and scalability.

Improved operational efficiency

Modernized systems eliminate redundant workflows, manual workarounds, and fragile integrations that slow down business processes. By streamlining core business operations, organizations reduce roadblocks and enable teams to work faster and more effectively.

Enhanced security and reduced risk

Outdated systems often contain unpatched vulnerabilities, unsupported frameworks, and weak access controls. Legacy system modernization strengthens security posture by leveraging modern infrastructure, improved identity and access management, encryption, and continuous monitoring, dramatically reducing the likelihood of security breaches.

Lower maintenance and operational costs

Legacy platforms often require expensive, specialized skills and ongoing maintenance. Modernizing legacy systems reduces licensing fees, infrastructure costs, and technical debt while shifting resources toward innovation instead of putting out fires. Over time, organizations often realize substantial cost savings.

Greater scalability and flexibility

Modernized systems, especially cloud-native architectures, scale dynamically to support business growth, seasonal demand, and future technological advancements. This flexibility allows businesses to respond quickly to market changes without major reengineering efforts.

Improved customer and employee experience

Faster applications, improved reliability, and better integrations directly impact customer experience. Internally, modern tools empower employees with intuitive interfaces, automation, and real-time insights that support productivity and morale.

Support for long-term digital transformation

Legacy application modernization lays the foundation for broader digital transformation initiatives. Modern systems integrate more easily with emerging technologies such as analytics, AI, and automation, ensuring organizations can continue evolving as technology evolves.

Why Is It Important to Modernize Legacy Systems?

Delaying legacy system modernization can often lead to serious security risks. As outdated software ages, it increasingly hinders innovation, exposes organizations to security threats, and limits the ability to meet evolving business needs.

Legacy systems often struggle to support modern compliance requirements, customer expectations, and integration demands. As vendors sunset support for outdated technologies, organizations face higher operational risks and fewer options for remediation.

From a business perspective, legacy platforms slow decision-making, complicate reporting, and restrict the ability to launch new products or services. Over time, these limitations erode competitiveness and constrain business growth.

Modernizing legacy applications ensures that technology supports business objectives. It allows organizations to align IT investments with strategic priorities, improve risk management, and build resilient systems that support future expansion.

Legacy Modernization Challenges

While the benefits are significant, legacy application modernization is not without challenges. It’s essential for technology teams to understand potential obstacles upfront to ensure that implementation goes smoothly.

Technical debt and system complexity

Many legacy environments have evolved over decades, resulting in tightly coupled systems, undocumented dependencies, and outdated code. Untangling these complexities requires deep technical expertise and careful planning.

Integration and data migration risks

Ensuring data accuracy during the migration process is one of the most common challenges. Poorly executed data migration can disrupt business operations, compromise reporting, and introduce compliance risks.

Operational disruption

Modernization efforts must balance progress with continuity. Without a phased approach and strong risk management, organizations risk downtime that impacts customers and critical business processes.

Security and compliance concerns

Legacy modernization initiatives often touch regulated data and systems. Maintaining compliance throughout the modernization process requires disciplined governance, security controls, and documentation.

Change management and organizational resistance

Modernizing legacy systems affects workflows, roles, and responsibilities. Without buy-in from business leaders and end users, even technically successful projects can fall short of adoption goals.

These challenges underscore why modernization should be treated as a strategic process instead of a purely technical upgrade.

How BD Emerson Can Help

BD Emerson’s Technology and Digital Transformation consultants specialize in guiding organizations through complex legacy application modernization efforts, leveraging decades of experience with hundreds of companies in diverse industries.

Our team begins every engagement with a comprehensive assessment of existing applications, infrastructure, security posture, and business processes. From there, our experts design a tailored legacy modernization strategy and roadmap aligned to your business goals and risk tolerance.

BD Emerson helps organizations:

• Define the right legacy modernization approach for each system

• Reduce technical debt while preserving business continuity

• Execute phased modernization initiatives that minimize operational risk

• Ensure data accuracy, security, and regulatory compliance throughout the process

• Leverage modern technologies and cloud-native solutions strategically

• Optimize costs while maximizing long-term business value

Whether you are modernizing a single legacy application or undertaking enterprise-wide legacy platform modernization, BD Emerson provides the technical expertise, governance, and execution support needed for a smooth transition.

Legacy application modernization is not a one-time project, but a modernization journey. With the right strategy, partners, and execution model, organizations can transform outdated systems into modern solutions that support innovation, resilience, and sustained business growth.

Ready to modernize your legacy systems?

Learn more about BD Emerson’s Digital Transformation Services and how our Technology Team can help future-proof your business.