There are altogether 7 migration strategies used to migrate a workload to the AWS Cloud. They are also called 7R's strategies for migration. We will discuss all the seven strategies one by one. First of all let us list all the seven strategies :

1. Rehosting

2. Replatforming

3. Retire

4. Retaining

5. Repurchase

6. Refactoring

7. Relocate

Rehosting

Rehosting is also called as Lift and Shift. This is a migration strategy where you move your applications without any changes meaning your applications are not altered while moving from your source environment to the AWS Cloud. Altogether 30 percent of your total cost is saved using Rehosting. For example: In the scenario of large legacy migration, in which the company is looking to implement its migration and scale quickly to meet a business case, the majority of applications are rehosted.

Replatforming

Replatforming is also known as "lift, tinker and shift". This involves making a few cloud optimizations to realize a tangible benefit. This kind of optimization is obtained without changing the core architecture of the application. For example: You could take your existing MySQL database and re-platform it onto RDS MySQL without any code changes at all.

Retire

There could be a scenario where some parts of your enterprise IT portfolio are just no longer needed. We can shut down the servers within the application stack which is no longer needed. Using the AWS migration plan as the opportunity to actually end-of-life these applications can save significant cost and effort for your team.

Retaining

This concept or strategy consists of keeping applications that are critical for business in the source environment. This might include applications that require major refactoring before they can be migrated or work that can be postponed until a later time. For example: (a) Some applications are about to be deprecated but maybe not just yet. (b) They still need to run but don't turn them off for another 3 months or eight months.

Repurchase

Repurchase involves moving from a traditional license to a software-as-a-service model. For example: A business might choose to implement the repurchasing strategy by migrating from a customer relationship management (CRM) system to salesforce . com. This involves replacing existing application with a cloud based version, such as software in AWS marketplace.

Refactoring

Other ways to name Refactoring is Re-architecting. This simply means your're writng a new code for your application. This is driven by a strong business need to add features or performance that might not be possible on premises, but now are within your reach. Dramatic changes to your architecture can be very beneficial to your enterprise but this will come at the highest initial cost in terms of planning and human effort. This uses cloud native features to improve performance, scalability and agility.

Relocate

This strategy involves transfer of large number of servers consisting one or more applications at a given time from on-premises platform to the cloud. This is also used to move your instances or objects to a different Virtual Private Cloud(VPC), Region or AWS Account. For example: you can transfer an Amazon Relational Database Service (Amazon RDS) database instance to another virtual private cloud or AWS Account.