The 7 Rs of Migration Strategy

Moving workloads to AWS is rarely a single action — it is a portfolio of decisions made for each application. The 7 Rs of migration give architects a common vocabulary to classify applications and choose the right migration path. For the SAA-C03 exam, you must know which R applies to a given scenario description, as questions often test your ability to match an application characteristic to the correct migration strategy.

Rehost (Lift-and-Shift) moves an application to AWS with no changes to the application code or architecture. Use AWS Application Migration Service (MGN) to replicate on-premises VMs to EC2 instances. Rehost is fastest to execute and carries the least risk, making it ideal for large-scale migrations where speed matters and optimisation can happen later. It does not take advantage of cloud-native features.

Replatform makes a few targeted cloud optimisations without changing the core application architecture. Examples: migrating a MySQL database from EC2 to Amazon RDS (managed patching, backups), or moving a Java app server to AWS Elastic Beanstalk (managed scaling). You keep the same application logic but replace operational heavy-lifting with managed services. This is a middle ground offering moderate benefit for low migration risk.

Repurchase replaces an existing application with a commercial SaaS product. Examples: replacing a self-managed CRM with Salesforce, or swapping a custom HR system for Workday. From AWS's perspective, this means cancelling the on-premises licence and subscription to a SaaS offering. The migration work is about data migration and user training rather than infrastructure. This is appropriate when the custom app no longer differentiates the business.

Refactor (Re-architect) involves redesigning the application to take full advantage of cloud-native capabilities. Examples: breaking a monolith into microservices running on Lambda and API Gateway, or re-implementing batch processing using SQS and auto-scaling workers. Refactor delivers the greatest long-term benefit in scalability, resilience, and cost — but it is the most expensive and time-consuming migration strategy.

Retire means shutting down applications that are no longer needed. A thorough portfolio assessment commonly finds that 10–20% of applications have no active users, duplicate functionality from another system, or are no longer fit for purpose. Retiring them reduces licencing costs, security surface area, and migration scope. Before retiring, confirm with stakeholders and check compliance data-retention requirements.

Retain (sometimes called Revisit) means keeping the application on-premises for now. Reasons include: regulatory requirements mandating data sovereignty, a recent capital investment in hardware, complex vendor dependencies, or the application is near end-of-life. Retained applications are not migrated in the current wave but may be re-evaluated later. Retain is a valid and common outcome of a migration assessment.

Relocate is the seventh R, added later to the framework. It moves infrastructure to AWS without purchasing new hardware, refactoring applications, or re-architecting. Specifically, it refers to migrating VMware vSphere workloads to VMware Cloud on AWS, allowing the same vCenter tooling to manage VMs now running on AWS bare metal. It is faster than rehost for VMware-heavy environments that are not ready to change OS or app.

In a real migration wave, a single organisation might apply all 7 Rs simultaneously: retire unused apps, retain compliance-blocked ones, rehost most with MGN, replatform databases to RDS, refactor one or two strategic monoliths to serverless, repurchase legacy CRM, and relocate VMware clusters. The AWS Migration Readiness Assessment (MRA) and Migration Hub help track each application's 7-R classification across the portfolio.

Migration cost increases as you move from Retire through Relocate, Retain, Rehost, Replatform, Repurchase, to Refactor. Refactor has the highest upfront engineering cost but typically yields the lowest long-term cloud spend due to serverless auto-scaling and pay-per-use billing. Rehost delivers the fastest time to cloud but may result in over-provisioned EC2 instances that need right-sizing afterwards to achieve cost savings.

Migration scenario questions follow a pattern: they describe an application characteristic and ask which migration strategy is most appropriate. Watch for keywords: 'fastest migration' = Rehost; 'managed service, no code change' = Replatform; 'modernise/serverless' = Refactor; 'move VMware' = Relocate; 'no longer needed' = Retire; 'compliance/data sovereignty' = Retain; 'switch to SaaS' = Repurchase. One correct R per scenario — eliminate the others using the keyword evidence.

Test your understanding of AWS Solutions Architect (SAA-C03) concepts from this lesson.

In this lesson you learned: the 7 Rs are Rehost, Replatform, Repurchase, Refactor, Retire, Retain, and Relocate, exam questions test your ability to match application characteristics to the correct R using keyword signals, and Refactor delivers the most cloud benefit but highest upfront cost. Next up we explore AWS Migration Hub and Application Discovery Service for portfolio assessment.