Mastering AWS Migration: The 5 Key Strategies and How to Choose

Migrating to AWS is more than just moving servers—it's about making strategic decisions that will impact your cloud costs, performance, and agility for years to come. In a large-scale migration of 340 applications from a private data center to AWS, the team met an aggressive deadline by applying different strategies to different workloads: 40% were lifted and shifted, 12% required full refactoring, and 8% were retired, delivering significant savings. Choosing the wrong strategy can lock in technical debt and inflate budgets. This guide covers the five most common AWS migration strategies—rehost, replatform, refactor, repurchase, and retire—including when to use each, key trade-offs, and practical insights to help you make the right choice.

1. What are the five main AWS migration strategies?

AWS's 7 Rs framework outlines migration approaches, but five are most commonly used in real-world projects. Rehost (Lift and Shift) moves applications to AWS EC2 with minimal changes—fast but often 15–25% more expensive initially. Replatform makes a few cloud-friendly optimizations (e.g., switching from a self-managed database to Amazon RDS) without full re-architecture. Refactor (Re-architect) fundamentally redesigns the application to leverage cloud-native features like serverless or microservices—costly but yields long-term benefits. Repurchase replaces the current software with a SaaS equivalent (e.g., moving from an on-prem CRM to Salesforce). Retire decommissions applications that are no longer needed, instantly cutting costs. The right mix depends on business goals, timeline, and application criticality. In the 340-app migration, 40% were rehosted for speed, 12% refactored for innovation, and 8% retired for savings.

Mastering AWS Migration: The 5 Key Strategies and How to Choose — Source: dev.to

2. When should you use the rehost (lift and shift) strategy?

Rehost is your go-to when speed is the priority. It involves copying the application onto AWS EC2 with almost no changes. Use it when: the data center lease is ending and you have weeks to vacate, compliance deadlines are immovable, or you need an early win to build migration momentum. It's also the right choice if the application is stable and not scheduled for major changes. However, be aware that rehosted apps typically run 15–25% more expensive on AWS in year one because you keep the same architecture without leveraging elasticity. That premium vanishes after optimization—but only if you actually go back and optimize. Many teams forget that step. Tools like AWS Application Migration Service (MGN) and CloudEndure automate much of the rehosting process, making it fast and reliable. But don't treat rehost as a permanent state; plan a post-migration optimization phase to reduce costs.

3. What is replatforming, and when does it make sense?

Replatforming sits between lift-and-shift and full refactoring. You modify the application slightly to take advantage of managed AWS services, but the core architecture stays the same. For example, you might move a MySQL database to Amazon RDS, or switch from an in-house load balancer to Elastic Load Balancing. This approach yields moderate cost savings and operational efficiency without a complete rewrite. Use replatforming when you need to modernize quickly but can't afford the time and risk of refactoring—for instance, when the current database version is near end-of-life and the cloud migration is the perfect time to upgrade. The trade-off: you gain benefits like automated backups and patching, but you still carry some legacy design constraints. It's a sweet spot for organizations that want to move forward without starting from scratch.

4. When is refactoring the right AWS migration strategy?

Refactoring (or re-architecting) means fundamentally redesigning the application to be cloud-native—think microservices, serverless functions, containers, or event-driven architectures. This is the most expensive and time-consuming strategy, so it's reserved for applications that will drive significant business value after modernization. Typical triggers: the app is a core revenue driver that needs to scale unpredictably, you have strong DevOps talent, or the current architecture is so brittle that changing any feature is risky. Refactoring slashes long-term operational costs and enables faster feature delivery. But it's not for every app. In the 340-app migration, only 12% were refactored. Avoid the temptation to refactor middleware or low-impact systems. A common mistake is team-wide refactoring mandates—instead, evaluate each application's potential return on investment before committing to a full rewrite.

5. What does the repurchase strategy involve?

Repurchase means retiring your current software and buying a cloud-based SaaS alternative. Instead of migrating a custom CRM, you subscribe to Salesforce. Instead of hosting an email server, you switch to Office 365. This strategy is ideal when the existing application is no longer competitive, requires heavy maintenance, or the vendor is sunsetting support. The biggest advantage is speed—you often just configure and deploy the new service, eliminating infrastructure management. However, be aware of vendor lock-in and data migration complexity. Also, employee training and workflow changes can cause temporary productivity dips. Repurchase is best for commoditized business functions like HR, payroll, or customer relationship management. For bespoke or highly integrated systems, refactoring or rehosting may be better. Always run a total cost of ownership analysis that includes subscription fees, migration costs, and lost productivity during the transition.

6. How can retiring applications drive cost savings?

Retiring an application means decommissioning it entirely—no migration, no rehost, no future cost. This is the most overlooked strategy, yet it often delivers the highest ROI. Many organizations run hundreds of applications that are unused, redundant, or have low business value. In the 340-app migration, retiring 8% of the portfolio led to outsized cost savings because those apps consumed resources without offering any return. To identify retire candidates, conduct an application portfolio assessment: analyze usage logs, interview business owners, and flag apps with no recent updates or user activity. Also consider applications that have been replaced by newer systems but still run out of inertia. Retiring them eliminates licensing fees, hardware maintenance, and operational overhead. The key is to have a formal sunset process—archive data, notify users, and remove dependencies. A well-executed retirement is a quick win for cloud budgets.

7. How do you choose the right migration strategy for each application?

Choosing the wrong strategy is one of the costliest mistakes in cloud projects. Refactoring unnecessarily inflates budgets, while thoughtless lift-and-shift embeds long-term technical debt. The best approach: treat each application individually. Start by categorizing apps by complexity, criticality, and business value. Use AWS's 7 Rs framework as a checklist. For stable, low-impact apps with tight deadlines, use rehost. For apps that need moderate modernization, choose replatform. For core strategic systems that require innovation, invest in refactoring. For obsolete functions, repurchase or retire. Always compute a rough cost comparison for each strategy—including operational overhead. Also factor in team skills: if your team lacks cloud-native expertise, refactoring may be risky. Finally, build a migration roadmap that mixes quick wins (rehost, retire) with longer-term modernization projects. Remember: a bad strategy decision in week 4 can become a $400K annual line item by year 3. Planning per application beats portfolio-wide mandates.

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