What are legacy systems? 

Legacy systems refer to old technology or computer systems that continue to be used by organizations despite the availability of newer alternatives. These systems often support critical business processes but can be based on outdated hardware or software, which makes maintenance challenging and costly.

The reliance on these aged technologies persists mainly due to the investment in their infrastructure and the potential risk and disruption associated with migrating to new systems. Legacy systems can be deeply integrated into a company’s core operations, causing companies to defer upgrading or replacing them due to concerns about business continuity.

This is part of a series of articles about application modernization.

What is legacy system modernization? 

Legacy system modernization involves updating or replacing legacy software or systems to enhance functionality, improve compatibility with newer technologies, and reduce maintenance efforts. This process can be crucial for adapting to current technological advances and improving operational efficiency.

The modernization can take various forms, from minor updates to existing code to a complete overhaul or replacement of the IT infrastructure. This is often driven by the need to integrate new functionalities, improve system performance, and address security vulnerabilities inherent in older systems.

Related content: Read our guide to mainframe modernization (coming soon)

Benefits of modernizing legacy systems 

There are severals reasons for organizations to modernize their legacy systems:

  • Improved performance and efficiency: Modernizing legacy systems typically leads to enhanced performance, reducing the time required to process data and execute tasks. New technologies optimize these processes, leading to quicker response times and a more efficient use of resources. 
  • Enhanced security and compliance: Replacing or upgrading legacy systems can reduce vulnerabilities and enhance security measures. Older systems often lack support and updates, leaving them susceptible to cyber-attacks. Modern systems bring improved security technologies, which are crucial for protecting sensitive data and avoiding potential breaches.
  • Improved user experience: New technologies allow for more intuitive, user-friendly interfaces that can lead to increased employee satisfaction and productivity. Users benefit from streamlined workflows and reduced complexity, which decreases training time and the likelihood of errors.
  • Cost savings: Modern systems typically require less maintenance and fewer resources to operate efficiently, which translates into reduced operational costs. Despite the initial investment for modernizing legacy systems, the long-term savings can be significant. 

Challenges of software modernization 

It’s also important to note the various challenges associated with modernizing legacy systems:

  • Complexity and dependencies: Legacy systems are often deeply embedded within an organization’s operations, making modernization a complex challenge. Their intricate architectures and the numerous dependencies on other systems and processes mean that upgrading or replacing one component can have unforeseen impacts across the IT landscape. They often have a tangled web of customizations accumulated over the years 
  • Skill gaps: As technology evolves, expertise in older systems becomes scarce, with fewer IT professionals proficient in outdated programming languages and architectures. This scarcity complicates efforts to maintain, troubleshoot, and upgrade legacy applications, as finding individuals with these skills can be challenging and costly.
  • High costs: Modernizing legacy systems is typically a resource-intensive endeavor, demanding significant financial and human capital investment. In addition to the initial costs associated with upgrading hardware, acquiring new software licenses, and migrating data can be substantial, the process often requires specialized consultants or developers that add to the project’s expense.
  • Risk of business disruption: During the transition to updated technologies, there’s a potential for system downtime or functionality loss, which can affect day-to-day operations and lead to revenue losses. This disruption impacts internal processes and can degrade the customer experience

Key system modernization strategies and approaches (7 Rs)

There are several ways to approach legacy system modernization. These are adapted from the Gartner 5 Rs model, which was later expanded to “7 Rs” by Amazon Web Services.


Replatforming involves moving applications, data, and other components from one environment to another without changing the core application architecture. It aims to harness the benefits of a new platform’s capabilities—such as improved performance, scalability, and security—while minimizing the changes to the application’s code. 

By doing so, organizations can reduce the impact on their operations and achieve modernization goals with less effort compared to a full system overhaul. The process typically includes minor code modifications, use of new platform features, and sometimes changes in the underlying database management system.


Refactoring is the process of restructuring existing computer code without changing its external behavior. It aims to improve the design, structure, and implementation of software while preserving its functionality. This approach allows developers to clean up the codebase, making it easier to understand, maintain, and extend. 

By refactoring legacy systems, organizations can address technical debt accumulated over years of operation and updates, enhancing system performance and scalability. However, it requires a deep understanding of both the existing system’s architecture and the desired improvements. Refactoring is often performed incrementally to keep the system operational.  


Rehosting, commonly known as “lift and shift,” involves transferring applications, data, and other components from an existing infrastructure to a new environment without modifying the application’s code. This approach is used to migrate legacy systems to cloud platforms quickly. 

It allows organizations to benefit from the cloud’s scalability and reliability without the complexities associated with altering application logic or architecture. This helps offload hardware management, reduce physical infrastructure costs, and leverage on-demand resource scaling. However, with the application code unchanged, some benefits of modern architectures may be lacking.


Rearchitecting involves completely redesigning the application’s architecture to support modern practices, such as microservices, enabling improved scalability, performance, and agility. This allows organizations to transform their legacy systems into more flexible, scalable, and manageable applications. 

By adopting a new architecture, organizations can incorporate contemporary technologies that support current and future business needs. It enables the adoption of cloud-native services, automated deployments, and continuous integration/continuous deployment (CI/CD) practices. However, rearchitecting requires significant effort and investment.  


Replacing involves the complete removal of a legacy system and its substitution with a modern solution that better meets business needs and technological standards. This approach is often considered when existing systems are too outdated for other modernization strategies. By implementing a new system, organizations can take advantage of the latest technologies.

The decision to replace a legacy system must consider the investment required to adopt new software or platforms. This includes potential data migration issues and the need to train staff to use the new system. However, replacing legacy systems also provides an opportunity to re-evaluate business processes and workflows, aligning them more closely with strategic goals. 


Retiring a legacy system involves decommissioning it so that it is no longer in use, often because its functionality has been replaced or is no longer needed. This helps eliminate redundant systems and reduces the complexity of the IT environment. By retiring outdated systems, organizations can focus on maintaining more critical systems.

The process of retiring a system requires careful planning to ensure that data preservation needs are met and that dependencies on the legacy system are addressed. It often involves migrating data to a new system or archiving it for compliance purposes.  


Retaining certain legacy systems can be a deliberate strategy when their functionality continues to meet business needs without compromising security or efficiency. Organizations may find continued value of existing investments and seek to avoid unnecessary disruption. Retention is viable for specialized applications where the challenges of modernization outweigh the benefits. 

However, this approach requires ongoing evaluation to ensure these systems remain useful, secure, and compliant with evolving standards. Organizations must implement regular security updates and compatibility checks with new technologies to ensure that retained systems do not become liabilities. 

Legacy software modernization best practices

Here are some of the measures that organizations can take to ensure a successful modernization strategy. 

Analyze your legacy IT architecture and systems 

Before modernizing legacy systems, it’s important to assess the current architecture and systems through six key drivers: business value, technology obsolescence, operational risks, agility and scalability, cost efficiency, and regulatory compliance. This analysis helps identify the critical areas for modernization by assessing how well existing systems support business goals. 

It also highlights systems that pose operational risks due to outdated technology or that hinder organizational agility due to their inflexible nature. Additionally, evaluating the cost efficiency of maintaining versus modernizing legacy systems can reveal opportunities for reducing operational expenses.  

Transition to cloud-native systems

Cloud-native systems leverage cloud computing’s full capabilities. This transition involves building and running scalable applications in modern, dynamic environments such as public, private, and hybrid clouds. It emphasizes the use of services and technologies inherent to the cloud to achieve more resilient, flexible, and scalable applications. 

By adopting a cloud-native approach, organizations can support continuous integration and delivery pipelines, enabling faster development cycles. Cloud-native systems use microservices architectures, containerization, orchestration tools like Kubernetes, and DevOps practices to enhance agility. Modularization of applications into smaller, independently deployable units makes them easier to manage.  

Embrace a devops methodology 

DevOps involves the integration of development and operations teams to improve collaboration, accelerate workflows, and enhance product quality. This approach emphasizes automation, continuous integration (CI), and continuous delivery (CD), enabling organizations to rapidly develop, test, and deploy software. 

By fostering a culture of open communication and shared responsibility, DevOps breaks down traditional silos that slow down development processes and hinder quick response to market changes. Incorporating DevOps practices allows for quicker identification and resolution of issues, leading to more stable releases and improved system reliability.  

Conduct a risk assessment 

It’s important to identify potential challenges and vulnerabilities early in the process. This enables organizations to prioritize issues based on their impact and likelihood, ensuring that resources are allocated appropriately to mitigate risks. Key areas of focus include security vulnerabilities, data integrity during migration, and compatibility between old and new systems.

By thoroughly assessing these risks, companies can build comprehensive strategies to address them, minimizing the chances of setbacks. Risk assessment should be an ongoing activity throughout the modernization process, identifying new risks as they emerge while others become less relevant.  

Ensure compliance 

Organizations must align updated or new systems with the relevant legal and regulatory standards. This requires an understanding of current and upcoming regulations. By integrating compliance checks at each stage of the modernization process, organizations can address potential legal issues, reducing the risk of non-compliance penalties and reputational damage.

Incorporating automated compliance tools can simplify this process, allowing for continuous monitoring and reporting on compliance status. These tools can help identify discrepancies early, enabling timely adjustments to comply with regulatory requirements. Documenting compliance efforts provides a clear audit trail, further protecting against legal challenges. 

Leverage modern technologies 

Integrating advanced tools and platforms into the modernization strategy can help optimize legacy system upgrades. This includes adopting cloud computing for scalability and flexibility, implementing artificial intelligence (AI) and machine learning (ML) for enhanced data analysis and decision-making, and utilizing Internet of Things (IoT) technologies for improved connectivity and insights. 

By embracing these technologies, organizations can enhance their operational efficiency, customer experience, and competitive edge. Leveraging modern development practices such as containerization and microservices architecture enables more efficient application deployment and management. 

Documenting legacy code with Swimm

Legacy code represents a significant challenge as well as an opportunity for software organizations. Managing legacy code entails more than just dealing with untidy or outdated code; it involves transforming it into a reliable and efficient foundation that supports future development initiatives. Handling legacy code effectively can lead to considerable long-term savings and heightened productivity, marking it as a strategic priority for any R&D organization. 

Swimm helps enterprise development teams document legacy code in an easy, manageable, and effective way. Utilize AI to create docs about legacy code and then discover those docs directly in your IDE. Those docs then stay up to date with ongoing code changes, boosting your team’s productivity and enhancing the quality of your codebase. 

Learn more about Swimm for legacy code