What are the six common migration strategies, often called the six Rs, and when would you recommend each one?

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The six Rs provide a framework for categorizing how each application or workload should be moved to the cloud. Choosing the right strategy depends on the application's architecture, business value, technical constraints, and the organization's timeline and budget.

Rehost, commonly called lift-and-shift, moves the application to the cloud with minimal or no changes. The application runs on cloud infrastructure but does not take advantage of cloud-native features. This is the fastest migration path and works well for applications with an urgent data center exit deadline or for applications that will be retired within a few years. It reduces infrastructure management overhead but does not improve the application architecture.

Replatform, sometimes called lift-tinker-and-shift, makes targeted optimizations during the migration without changing the core architecture. Examples include migrating from a self-managed database to a managed database service like Amazon RDS or Azure SQL Database, or moving from a self-managed message broker to a managed service like Amazon SQS. Replatforming captures some cloud benefits such as reduced operational overhead and improved availability while keeping migration risk low.

Refactor or re-architect involves significantly redesigning the application to take full advantage of cloud-native capabilities. This might mean breaking a monolith into microservices, adopting serverless functions, or implementing event-driven architecture. Refactoring delivers the greatest long-term benefits in terms of scalability, performance, and development velocity, but it requires the most time and investment. It is best suited for applications that are strategic to the business and need to scale or evolve significantly.

Repurchase means replacing the existing application with a different product, typically a SaaS solution. For example, migrating from an on-premises CRM to Salesforce or from a self-hosted email server to Microsoft 365. This makes sense when a commercially available product meets the business needs better than maintaining a custom application.

Retire involves decommissioning applications that are no longer needed. During migration assessment, organizations often discover redundant or unused applications that can simply be turned off. This reduces the migration scope and saves licensing and maintenance costs.

Retain means keeping certain applications in the current environment, at least temporarily. Some applications may have compliance requirements, hardware dependencies, or recently completed upgrades that make immediate migration impractical. These applications are revisited in a future migration wave.

A typical migration portfolio uses a mix of all six strategies. I recommend starting the assessment by evaluating each application against business value and migration complexity, then assigning the most appropriate R based on the organization's priorities, timeline, and risk tolerance.