Each application has it's unique significance, own technical setup and enjoys a separate phase of it's life. This just tells us that the migration strategies on these applications has to be different to derive the maximum benefit out of our plans.

The "7 Rs" of cloud migration strategies crisply consolidates different approaches for migrating applications to the cloud. Each "R" signifies a strategy: Rehost, Refactor, Revise, Rebuild, Rearchitect, Replatform, and Retire.

These strategies help organizations make informed decisions about how to migrate their applications based on factors such as cost, complexity, and business goals. Each strategy provides a different level of effort and offers unique benefits, allowing businesses to choose the most suitable one for their specific applications.

By understanding and applying the 7 Rs, organizations can simplify their migration plans, reduce risks, and maximize the benefits of cloud adoption.

Migration Strategies

Having discussed the importance of the "7 Rs" of cloud migration strategies as a whole, let's analyze each of these strategies separately along with their use cases.

As depicted in the diagram above, we can place these 7 strategies into the following groups for the ease of our understanding:

I. Simple & Quicker Migrations
II. Migrations Needing Major Changes
III. Migrations To Cloud Not Needed

I. Simple & Quicker Migrations

1. Relocate

Relocation is the simplest migration strategy, and it involves moving your applications and data to a new cloud environment without making any changes.

This is a good strategy for applications that are already cloud-ready and that don't need to be modernized.

Sample Use Case:

1. Migrating an on-premises MySQL database to Amazon RDS.
   
2. Migrate the on-premise containerized workloads to Amazon Elastic Container Services.

2. Rehost

Rehosting, also known as "lift and shift," is another simple migration strategy. It involves moving your applications and data to the cloud without making any changes to the code or architecture.

This is a good strategy for applications that are not cloud-ready but, we want to take the benefits of migrating to cloud now and take up the long term modernization or repurchase plans later in phases.

Sample Use Case:

1. Rehost with Existing Configuration: An organization has virtualized its servers on-premise using VMware and wants to move to cloud without any major changes in it's server configurations.

Using the rehost strategy, the organization can use AWS Application Migration Service to replicate virtual machines to Amazon EC2 instances. The existing VM configurations are rehosted as EC2 instances, allowing seamless migration without major modifications.

2. Rehost Servers at Scale & Modernize Later: We can use AWS Application Migration Service (AWS MGN), a highly automated lift-and-shift (rehost) solution to lift-and-shift a large number of physical, virtual, or cloud servers without compatibility issues, performance disruption, or long cutover windows. This can expediate the process of migration, so that the long term modernization plans can be taken up later as per the organization's budget and schedules.

3. Replatform

This is a good strategy for applications that are not cloud-ready but, that can be modernized with relatively minor changes.

Sample Use Case:

1. Migrate a mid-sized e-commerce application to AWS Elastic Beanstalk, taking advantage of its automatic scaling and management capabilities.
2. Migrate your self-managed database to Amazon RDS (Relational Database Service), a managed database service by AWS. By replatforming to RDS, the organization offloads database management tasks, such as backups, patching, and scaling, to AWS, allowing the team to focus on application development.

II. Migrations Needing Major Changes

4. Refactor:

Restructure applications to optimize them for cloud environments, often using microservices, serverless or other modernizing options.

Sample Use Case:

1. Decompose a monolithic application into microservices and deploy them using Amazon ECS for better scalability and flexibility.
   
2. An organization wants to migrate and improve it's chatbots system. The chatbot logic can be refactored into AWS Lambda functions integrated with Amazon Lex, a natural language processing service. When a user interacts with the chatbot, the corresponding Lambda function is triggered by Lex's events. By using Lambda, the organization achieves a highly responsive, event-driven chatbot system that scales automatically based on demand, ensuring efficient and personalized user interactions.

5. Repurchase

Replace existing software with a cloud-based alternative as part of being cloud-ready or modernization.

Sample Use Case:

1. Replace an on-premise CRM system with a SaaS solution like Salesforce for advanced CRM capabilities.
   
2. The firm repurchases financial software by migrating to AWS QuickBooks, a cloud-based accounting solutions.

III. Migration to Cloud Not Needed

6. Retire

This is a strategy to identify and eliminate redundant, obsolete applications.

Sample Use Case:

1. Phasing out an outdated version of an API endpoint and asking customers to move to the new advanced version.
2. Eliminating an obsolete application monitoring system and replacing it with the standard alternatives used for other applications.

7. Retain

Keep certain applications on-premise due to regulatory or technical constraints.

In scenarios where retaining applications on-premise is necessary but operational simplicity of the AWS cloud environments is desired, AWS provides tailored solutions like AWS Outposts, AWS ECS Anywhere, and AWS EKS Anywhere. These offerings can ensure seamless integration between on-premise infrastructure and the cloud.

Sample Use Case:

1. Retain applications dealing with sensitive customer data on-premise due to legal regulations while migrating other non-sensitive applications to the cloud.
   
2. An organization has a mission-critical, legacy application that cannot be migrated due to compliance or regulatory constraints.