Comparing Legacy Application Migration Approaches: Rehosting, Replatforming, and Refactoring In the rapidly evolving technological landscape, businesses often find themselves needing to upgrade or modernize their existing applications to remain competitive. Legacy applications—systems built on outdated frameworks or infrastructure—pose numerous challenges in terms of performance, security, and scalability. As a result, many organizations are considering legacy application migration to cloud environments or newer frameworks to harness the benefits of modern infrastructure. However, not all migration strategies are alike. Three primary approaches stand out: Rehosting, Replatforming, and Refactoring. This article explores these strategies in detail, outlining the pros, cons, and considerations for each to help you make informed decisions about your legacy application migration journey. Understanding Legacy Application Migration Legacy application migration involves transferring old or outdated applications to newer platforms, infrastructures, or cloud environments. By doing so, businesses can improve performance, lower maintenance costs, and increase security. Additionally, migrating legacy applications allows companies to harness cloud-native technologies, access new capabilities, and support business growth in ways that on-premises or outdated systems cannot. Legacy migration is not a one-size-fits-all approach; it varies based on an organization’s goals, budget, timelines, and technical requirements. The three major approaches to legacy migration—Rehosting, Replatforming, and Refactoring—each serve different purposes and levels of modernization. Here’s a closer look at each method: 1. Rehosting (Lift and Shift) Definition: Rehosting, commonly referred to as the "lift and shift" approach, involves moving an application from an on-premises environment to a cloud-based infrastructure with minimal or no modifications to the application itself. This strategy is often chosen when the organization wants to move quickly and doesn’t want to invest heavily in redesigning the system. Process: Rehosting typically involves minimal changes, such as redirecting the application’s network or configuration settings to function in a cloud environment. This process can often be automated using migration tools from cloud providers like AWS (with their CloudEndure Migration), Google Cloud (with Velostrata), or Microsoft Azure (with Azure Migrate). Pros of Rehosting: Speed: Rehosting is one of the fastest ways to move to the cloud, as it requires minimal changes to the application. Cost-Effective: It involves lower upfront costs because it doesn’t require redesigning or re-architecting the application. Minimal Disruption: Since there’s little to no change to the application’s code, the process tends to be less disruptive for end-users and IT teams. Cons of Rehosting: Limited Cloud Optimization: Because the application is essentially “lifted and shifted” as-is, it may not take full advantage of cloud-native capabilities such as elasticity, serverless options, or managed services. Maintenance Challenges: Applications remain in their legacy form, which can lead to increased maintenance and support needs in the long term. Scalability Limitations: Legacy applications may not scale as efficiently in the cloud as cloud-native applications, potentially limiting growth. Best for: Rehosting is ideal for organizations that need to move quickly to the cloud for cost savings or disaster recovery, and where minimal changes can meet their short-term needs. For example, if an enterprise wants to consolidate its data centers and reduce infrastructure costs, rehosting may be a good option. 2. Replatforming (Lift, Tinker, and Shift) Definition: Replatforming, also known as "lift, tinker, and shift," involves moving an application to the cloud while making some optimizations to improve performance, scalability, or cost-efficiency. This approach makes minor changes to the application but does not involve a complete redesign or refactoring. Process: During replatforming, certain components of the application are optimized to leverage cloud services. For instance, a database might be migrated from on-premises to a managed database service, or some components may be containerized to facilitate scalability. Pros of Replatforming: Improved Cloud Compatibility: By optimizing certain aspects, replatforming enables applications to benefit from some cloud-native features, such as automated backups, managed databases, or containerization. Better Cost Management: Moving to managed cloud services can lower operational costs associated with maintaining and updating infrastructure. Enhanced Performance: Applications often see improved performance by using cloud-optimized services, which can lead to faster processing and better scalability. Cons of Replatforming: Moderate Investment Required: Although it’s not as intensive as refactoring, replatforming does require some level of customization, which increases time and cost compared to rehosting. Potential Complexity: Applications may experience compatibility issues as they are partially optimized, which can complicate troubleshooting and maintenance. Limited Scalability Gains: Since replatforming doesn’t entirely modernize the application, some scalability limitations of the legacy architecture may persist. Best for: Replatforming works well for applications that need some level of optimization for improved performance or scalability but don’t require full modernization. This approach is often chosen by organizations that want to move closer to cloud-native models without incurring the high costs of a complete refactor. 3. Refactoring (Rearchitecting) Definition: Refactoring, or rearchitecting, involves a comprehensive transformation of an application to fully leverage cloud-native capabilities. This approach entails rebuilding significant portions of the application’s code and architecture to achieve scalability, flexibility, and efficiency in the cloud environment. Process: Refactoring may involve decoupling monolithic applications into microservices, implementing containerization, or adopting serverless architectures. The process is intensive and requires in-depth planning, skilled development teams, and significant time investment. Pros of Refactoring: Maximized Cloud Potential: Refactoring allows applications to fully benefit from cloud-native features, such as autoscaling, serverless functions, microservices, and managed databases. Long-Term Cost Efficiency: Though initially costly, refactoring often leads to lower long-term maintenance costs due to the application’s enhanced scalability and compatibility with cloud infrastructure. Enhanced Flexibility and Performance: Refactoring enables the application to scale seamlessly and perform optimally in a cloud environment, potentially leading to better user experience and operational efficiency. Cons of Refactoring: High Upfront Costs: Refactoring is the most expensive approach due to the extensive development work required. Extended Timelines: This approach takes more time, which could lead to disruptions in business operations if not planned effectively. Increased Complexity: The transformation from a legacy structure to a modernized, cloud-native architecture can introduce new complexities in testing, deployment, and maintenance. Best for: Refactoring is ideal for organizations seeking to fully modernize applications to meet long-term business goals. This approach suits applications that are critical to the organization and need to scale efficiently with future growth. For example, a large e-commerce platform that experiences high traffic fluctuations may benefit significantly from refactoring to ensure optimal performance during peak times. Choosing the Right Approach Choosing between rehosting, replatforming, and refactoring depends on several factors, including: Budget: Refactoring generally requires a larger budget due to extensive development, while rehosting is the most cost-effective. Timeline: Rehosting is the fastest, making it ideal for urgent migrations, while refactoring requires a longer timeline. Business Goals: Organizations looking for quick cost savings may lean towards rehosting, while those aiming for long-term scalability and modernization may prefer refactoring. Technical Debt: Applications with significant technical debt might benefit from refactoring to ensure they are maintainable and scalable in the cloud. Application Complexity: Highly complex applications may require refactoring for optimal cloud performance, while simpler applications may perform adequately with rehosting or replatforming. Case Study Examples Rehosting for Cost Savings: A financial services firm rehosts its legacy applications to AWS to reduce on-premises data center costs and leverage AWS’s pay-as-you-go model. By rehosting, they achieve immediate cost savings without altering their business logic. Replatforming for Improved Performance: A retail company moves its inventory management system to a managed cloud database service, improving query performance and data access speeds. By replatforming, they achieve performance gains without fully rewriting the application. Refactoring for Scalability: A media streaming company breaks down its monolithic application into microservices, allowing each service to scale independently. Refactoring enables them to handle peak traffic efficiently, providing a seamless experience to end-users. Conclusion [Legacy application migration](https://gloriumtech.com/legacy-application-migration/) is essential for organizations aiming to stay competitive and leverage the advantages of cloud computing. Rehosting, replatforming, and refactoring each offer unique benefits and challenges, making it crucial for businesses to choose the approach that aligns with their goals, budget, and technical requirements. In summary: Rehosting offers a quick, cost-effective migration but lacks deep cloud optimization. Replatforming balances cloud optimization with a moderate investment, suitable for improving performance without a complete overhaul. Refactoring delivers the most value through cloud-native transformation but requires significant time, cost, and expertise. Selecting the right migration strategy can help organizations achieve improved performance, scalability, and cost savings, ultimately transforming their legacy systems into agile, modernized applications that support business growth.