AWS Migration Strategies – The 6 R‘

1. Rehost ("Lift and Shift")

What it is: Moving applications from your on-premises environment to AWS without making any changes to the application's architecture. The servers, operating systems, and applications are simply "lifted" from the source environment and "shifted" to AWS infrastructure (e.g., onto Amazon EC2 instances).
When to use it:
- You are looking for a rapid migration to exit a data center quickly.
- You are migrating a large number of applications in a short timeframe.
- The application is a legacy system that cannot be easily modified.
- You are in the early stages of your cloud journey and want to build experience.
Key Characteristics:
- Pros: Fastest migration path, lowest complexity, minimal risk of breaking the application.
- Cons: Does not take advantage of cloud-native features (like auto-scaling or serverless), potentially leading to higher long-term costs and less operational efficiency compared to other strategies.

What it is: A modification of "lift and shift" where you make a few targeted cloud optimizations to achieve tangible benefits without changing the core architecture of the application. For example, moving an on-premises Oracle database to Amazon RDS for Oracle.
When to use it:
- You want to reduce the burden of managing databases or other standard components.
- You want to see immediate benefits from the cloud (e.g., improved performance, managed backups) with minimal development effort.
- The application is compatible with a managed service offering.
Key Characteristics:
- Pros: Achieves a good balance of speed and cloud benefits, reduces operational overhead.
- Cons: Risk of unforeseen issues during the "reshape" phase, requires more testing than a simple rehost.

What it is: Moving to a different product, typically by ending an existing licensing agreement and repurchasing a new, cloud-native solution. This often means moving from a traditional, on-premises application to a Software-as-a-Service (SaaS) product.
When to use it:
- Your existing legacy application or license is nearing its end-of-life.
- A SaaS solution offers a better feature set or a more favorable cost model (e.g., moving from an on-premises CRM to Salesforce).
- You want to completely offload application management.
Key Characteristics:
- Pros: Eliminates development and infrastructure management, predictable costs, immediate access to modern features.
- Cons: Potential data migration challenges, possible loss of custom features, vendor lock-in.

What it is: Fundamentally re-imagining and rebuilding the application, typically using cloud-native features to improve performance, scalability, and cost-efficiency. This often involves moving from a monolithic architecture to microservices, or leveraging serverless technologies like AWS Lambda.
When to use it:
- There is a strong business need for new features, better performance, or higher scale that the existing architecture cannot support.
- The current application is becoming too expensive or difficult to maintain.
- You want to fully leverage the benefits of the cloud for a business-critical application.
Key Characteristics:
- Pros: Highest potential for optimization and long-term benefits, creates a highly resilient and scalable application.
- Cons: The most expensive and time-consuming strategy, highest risk, requires significant expertise.

What it is: Identifying and decommissioning applications in your IT portfolio that are no longer useful or are redundant. The functionality they provide is either not needed or is already offered by other systems.
When to use it:
- During the discovery phase, you find applications that are no longer used by the business.
- The functionality of an application has been absorbed by another, more modern system.
- The business value provided by the application is less than its cost of ownership.
Key Characteristics:
- Pros: Immediate cost savings in hardware, software licensing, and operational support. Simplifies the overall IT portfolio.
- Cons: Requires careful analysis and business confirmation to ensure the application is truly no longer needed.

What it is: Deciding to keep certain applications in your source environment. These are applications that you are not ready to migrate and will be revisited at a later time.
When to use it:
- The application is subject to strict regulatory or data residency requirements that are not yet met by the cloud.
- The application is a highly sensitive, critical system that you are not comfortable moving yet.
- A major refactoring is planned for the application in the future, and it makes more sense to migrate it then.
- There is no immediate business justification for the cost and effort of migration.
Key Characteristics:
- Pros: No immediate cost or effort required, allows you to focus on higher-priority migrations.
- Cons: Does not benefit from any cloud advantages, continues to incur on-premises operational costs.