Formulating the 6 Rs Strategies

The 6 Rs strategies are six methods for migrating existing applications and data to the cloud. The following figure illustrates the strategies.

Figure 1 6 Rs strategies

The following table describes the meaning and application scenarios of the 6 Rs strategies.

**Table 1** Descriptions and application scenarios of the 6 Rs strategies
Strategy	Description	Application Scenario
Retire	This strategy can stop applications or their components when they are unnecessary or there are more suitable alternatives. This is not a strict migration, but the elimination of existing applications.	The applications are no longer used by businesses. The functions of the applications have been replaced by other systems. The applications require high maintenance yet provide minimal business benefits. The applications are outdated, and they are difficult to maintain and upgrade.
Retain	This strategy keeps applications in their current states without migrating them. This is usually a short-term strategy or temporary measure during ongoing IT strategy development.	The applications depend on specific hardware or software and cannot be easily migrated. Application migration is risky, and there is no urgent need for migration in the short term.
Rehost	Also known as "direct migration" or "lift and shift", this strategy is used to migrate applications from an on-premises data center to the cloud platform without making any change to the applications. This strategy usually employs specific tools to convert virtual machines or physical servers into cloud-based virtual machines.	A quick migration to a cloud platform is required to reduce costs or improve availability. The migration must be expedited as time is critical. There is a lack of in-depth understanding of applications or resources to modify the code.
Replatform	This strategy involves making slight changes to applications during migration to fit the cloud platform. For example, migrate applications from an on-premises database to a cloud-based one. This does not involve modifying the core application code.	PaaS services, such as databases and message queues, on the cloud platform are required to ease the O&M burden of self-built databases and message queues. The performance or scalability of applications needs to be improved. No large-scale code modification is required, but optimizing application performance on the cloud platform is required.
Rearchitect	This strategy involves rewriting or refactoring application code for them to fit the cloud-native architecture. For example, a monolithic application can be refactored to a microservice architecture or switched to a serverless, event-based model.	The performance, scalability, and maintainability of applications need to be significantly improved. Cloud-native technologies, such as containers and serverless computing, are required. The application architecture is outdated and difficult to maintain and scale.
Replace	This strategy involves replacing existing applications with new applications or services. It typically means purchasing Software as a Service (SaaS) products or other new applications.	Existing applications cannot meet business requirements. Maintaining existing applications costs too much, and there are more suitable alternatives. Mature SaaS products are available in the market to meet business requirements. New functions and services need to be quickly deployed.

Among the 6 Rs strategies, only Rehost, Replatform, and Rearchitect are involved in migration to the cloud. The following table compares these three strategies. Enterprises can select the most suitable migration strategy based on their service requirements, application scenarios, and the migration risks, period, costs, difficulty, and benefits of each strategy.