This chapter covers the seven common migration strategies (the 7 Rs) for moving applications and workloads to AWS. Understanding these strategies is critical for the CLF-C02 exam, as it tests your ability to recommend the right approach based on business and technical requirements. This objective falls under Domain 1: Cloud Concepts (estimated 24% of the exam), and migration strategy questions appear frequently, often as scenario-based multiple-choice items.
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Imagine you've lived in a house for 20 years and need to move to a new city. You have seven strategies. First, you could simply buy an identical pre-built house in the new city (Rehost – lift and shift). Second, you might upgrade your old furniture before moving (Replatform – lift, tinker, shift). Third, you could demolish your old house and build a custom modern home (Refactor / Re-architect). Fourth, you could sell your house and buy a new one, keeping only the land (Repurchase – move to SaaS). Fifth, you might keep your house where it is but stop using it, and rent a new house (Retire – decommission). Sixth, you could keep your house but move only the most valuable items (Retain – keep as is). Finally, you might move to a hotel and never own a home again (Migrate with a partner – use a migration service). Each method has different cost, effort, and disruption. AWS's 7 Rs are exactly these strategies for moving applications to the cloud. The mechanism: you assess each application's business value, technical complexity, and dependencies, then choose the strategy that minimizes risk and cost while maximizing cloud benefits. Just like moving homes, you don't want to demolish a perfectly good house, but you also don't want to move a crumbling shack.
What Are the 7 Rs? The 7 Rs are a framework developed by AWS to categorize the strategies for migrating applications to the cloud. They help organizations evaluate each workload and choose the most appropriate migration path. The 7 Rs are: Rehost, Replatform, Refactor/Re-architect, Repurchase, Retire, Retain, and Relocate (sometimes included as an eighth R, but the classic 7 are the core). The problem they solve: every application is different, and a one-size-fits-all migration approach leads to cost overruns, delays, and technical debt. By using the 7 Rs, you can tailor the migration to each workload's characteristics.
How the 7 Rs Work – The Mechanism
Each R represents a different level of change to the application. The decision process typically starts with an application discovery and assessment using tools like AWS Migration Hub, AWS Application Discovery Service, and AWS Migration Evaluator. For each application, you assess:
Business criticality
Technical complexity (dependencies, architecture)
Licensing costs
Performance requirements
Security and compliance needs
Then you map the application to one of the 7 Rs. AWS provides a Migration Portfolio Assessment (MPA) tool to automate this. The exam expects you to know the definition of each R and when to use it.
Detailed Breakdown of Each R
1. Rehost (Lift and Shift) - What it is: Moving the application as-is from on-premises to the cloud with minimal changes. You take a snapshot of the server, replicate it on an EC2 instance, and redirect traffic. - Mechanism: Use AWS Server Migration Service (SMS) or CloudEndure Migration to replicate servers. The application runs on EC2 with the same OS, same configuration, same software stack. - When to use: When you need to migrate quickly, when the application is simple, or when you lack skills to modify it. - Exam tip: Rehost is the fastest and lowest-risk migration but may not fully leverage cloud benefits like auto-scaling or managed services.
2. Replatform (Lift, Tinker, and Shift) - What it is: Making a few cloud-optimized changes without altering the core architecture. For example, moving a database from self-managed Oracle on EC2 to Amazon RDS for Oracle, or moving from a web server on EC2 to AWS Elastic Beanstalk. - Mechanism: You modify the application stack to use managed services (e.g., RDS, ElastiCache, S3) but the application code remains largely unchanged. This reduces operational overhead. - When to use: When you want to gain some cloud benefits (like managed backups, patching) without a full rewrite. - Exam tip: Replatform is a middle ground – more effort than Rehost but less than Refactor.
3. Refactor / Re-architect - What it is: Completely redesigning the application to be cloud-native, often using microservices, serverless (AWS Lambda), containers (ECS/EKS), and managed services. - Mechanism: You break a monolithic application into smaller, independent services. Use API Gateway, Lambda, DynamoDB, SQS, etc. This is a major development effort. - When to use: When the current architecture is limiting business agility, when you need massive scalability, or when you want to reduce costs long-term. - Exam tip: Refactor is the most expensive and time-consuming but offers the most benefits.
4. Repurchase - What it is: Moving from a current license-based product to a SaaS alternative. For example, replacing a custom CRM with Salesforce, or replacing an on-premises email server with Microsoft 365. - Mechanism: You stop using the old application and adopt a cloud-based SaaS product. Data migration may be needed. - When to use: When a SaaS product meets your needs and reduces maintenance overhead. - Exam tip: Repurchase often involves changing vendors, not just moving to AWS.
5. Retire - What it is: Decommissioning applications that are no longer needed. Many organizations have zombie applications running on-premises that no one uses. - Mechanism: Identify unused or redundant applications through discovery tools, then shut them down. This reduces costs immediately. - When to use: During migration planning – you might find 10-20% of applications can be retired. - Exam tip: Retiring applications is a quick win for cost savings.
6. Retain - What it is: Keeping some applications on-premises for now. Reasons include: regulatory compliance, latency requirements, or the application is too complex to migrate. - Mechanism: You decide to postpone migration for certain workloads. They stay in the current environment. - When to use: When migration is not feasible or beneficial at the moment. You may revisit later. - Exam tip: Retain is a valid strategy – not every application must migrate immediately.
7. Relocate - What it is: Moving large-scale workloads from one hypervisor to another, typically from on-premises VMware to AWS VMware Cloud on AWS. This is a specific variant of Rehost for VMware environments. - Mechanism: Use VMware Cloud on AWS to run VMware workloads natively on AWS hardware. You can migrate without changing VM formats. - When to use: When you have a heavy investment in VMware and want to minimize changes. - Exam tip: Some sources list 6 Rs (excluding Relocate) or 7 Rs including Relocate. CLF-C02 typically tests the classic 7: Rehost, Replatform, Refactor, Repurchase, Retire, Retain, Relocate.
Comparison to On-Premises
In on-premises environments, changing an application requires buying new hardware, waiting for delivery, and manual migration. The 7 Rs provide a structured approach to move to the cloud with minimal disruption. AWS also offers the AWS Migration Acceleration Program (MAP) to help customers with funding and tools.
When to Use Each Strategy – Decision Flow
Is the application needed? No -> Retire
Is a SaaS alternative acceptable? Yes -> Repurchase
Is the application simple and can move as-is? Yes -> Rehost
Can we make minor optimizations? Yes -> Replatform
Does the application need to be modernized? Yes -> Refactor
Is it a VMware workload? Consider Relocate
Otherwise, Retain for now.
Pricing Models
Migration itself has costs: tools (e.g., CloudEndure Migration is free for the first 90 days), partner services, and development hours. AWS offers the Migration Hub to track progress. The exam tests your ability to recommend a strategy based on cost and effort.
Assess Current Environment
Begin by discovering all applications, servers, databases, and dependencies. Use AWS Application Discovery Service (agentless or agent-based) to collect data about on-premises infrastructure. This includes CPU, memory, storage, network usage, and inter-application dependencies. AWS Migration Hub provides a central place to track the assessment. The output is a list of applications with their technical specifications and business context. This step is critical because you cannot choose a migration strategy without understanding what you have. Common mistake: skipping dependency mapping, which leads to broken applications after migration.
Categorize Applications with 7 Rs
For each application, assign one of the 7 Rs based on business value, technical complexity, and migration goals. Use the AWS Migration Portfolio Assessment (MPA) tool to automate this. The tool asks questions about the application and suggests a strategy. For example, a legacy CRM that is critical but poorly documented might be a candidate for Rehost. A custom .NET application with high traffic might be a candidate for Replatform to use Elastic Beanstalk. Document the rationale for each decision.
Plan and Prepare Migration
For each application, create a migration plan. For Rehost, you might use AWS SMS to replicate servers. For Replatform, you might set up RDS and modify connection strings. For Refactor, you would design a new architecture using microservices. Prepare the target AWS environment: set up VPCs, subnets, security groups, IAM roles, and connectivity (VPN or Direct Connect). Test the migration in a sandbox account. AWS provides the Migration Hub to track tasks and status.
Execute Migration
Perform the actual data transfer and cutover. For Rehost, use CloudEndure Migration or AWS SMS to replicate servers continuously until cutover. For Replatform, migrate databases using AWS DMS (Database Migration Service) with minimal downtime. For Refactor, deploy new code using CI/CD pipelines (CodePipeline, CodeBuild). During cutover, redirect traffic from on-premises to AWS, often using Route 53 with weighted routing or a load balancer. Monitor the application for errors and roll back if necessary.
Optimize and Validate
After migration, optimize the workload for cost and performance. For Rehosted applications, consider rightsizing EC2 instances, adding auto-scaling, and using Reserved Instances or Savings Plans. For Replatformed applications, enable automated backups and patching. For Refactored applications, monitor with CloudWatch and X-Ray. Validate that the application meets SLAs. Finally, decommission the on-premises resources to avoid double costs. AWS Trusted Advisor can provide recommendations.
Scenario 1: Legacy Data Center Migration
A large financial institution has 500 servers running a mix of Windows and Linux applications. They are under pressure to close their data center within 12 months. Business Problem: They need to move quickly with minimal risk. Solution: They use a Rehost strategy for 80% of their applications, using CloudEndure Migration to replicate servers to EC2. For their Oracle databases, they use Replatform to move to Amazon RDS for Oracle, gaining automated backups and patching. For a custom trading application that requires low latency, they retain it on-premises initially due to regulatory constraints. Cost: They save on hardware refresh costs but pay for EC2 instances. Misconfiguration: They initially forgot to decommission old servers, leading to double costs for six months.
Scenario 2: E-commerce Modernization
A mid-sized e-commerce company runs a monolithic PHP application on a single server. They are experiencing performance issues during peak traffic. Business Problem: The application cannot scale. Solution: They choose Refactor to break the monolith into microservices using AWS Lambda, API Gateway, DynamoDB, and SQS. They also use Amazon CloudFront for content delivery. This allows auto-scaling and cost savings during low traffic. Cost: Higher initial development cost but lower operational cost over time. What goes wrong: They underestimated the complexity of refactoring, leading to a 6-month delay. They also faced data consistency issues because they moved from a relational database to DynamoDB without proper design.
Scenario 3: SaaS Adoption for CRM
A small business uses an on-premises CRM that requires manual updates and hardware maintenance. Business Problem: They want to reduce IT overhead. Solution: They choose Repurchase by migrating to Salesforce, a SaaS CRM. They use AWS DMS to migrate customer data to Salesforce's cloud. Cost: They move from capital expense (server hardware) to operational expense (monthly subscription). Misconfiguration: They did not clean up duplicate records before migration, causing data quality issues in the new system.
What CLF-C02 Tests on This Objective
The exam tests your ability to identify and differentiate the 7 Rs. You will see scenario-based questions where you must recommend the best migration strategy. Domain: Cloud Concepts (Objective 1.3 – Describe the benefits of and strategies for migration to the AWS Cloud). Expect 2-4 questions on this topic.
Most Common Wrong Answers and Why
Choosing Rehost when the scenario mentions 'modernize' or 'cloud-native' – Candidates see 'move to cloud' and pick Rehost, but the question asks for the best strategy to leverage cloud benefits like auto-scaling. The correct answer is Refactor.
Choosing Retire when the application is still needed – Candidates think retiring saves cost, but if the business uses it, Retire is wrong. The correct answer might be Rehost or Replatform.
Confusing Replatform with Refactor – Replatform involves minor changes (e.g., moving a database to RDS), while Refactor involves rewriting code. The exam tests this distinction.
Thinking Retain means 'do nothing' – Retain means keep on-premises, not ignore. It is a deliberate decision.
Specific Terms That Appear Verbatim on the Exam
'Lift and shift' for Rehost
'Lift, tinker, and shift' for Replatform
'Cloud-native' for Refactor
'SaaS' for Repurchase
'Decommission' for Retire
'Hypervisor' for Relocate (VMware)
Tricky Distinctions
Rehost vs. Replatform: If the question says 'minimal changes' or 'as-is', it's Rehost. If it says 'minor optimizations like managed database', it's Replatform.
Refactor vs. Repurchase: Refactor changes your own code; Repurchase replaces with a third-party SaaS.
Retire vs. Retain: Retire removes the application; Retain keeps it on-premises.
Decision Rule for Multiple Choice
Read the scenario: Is the application still needed? If no, Retire.
Is there a SaaS alternative that meets needs? If yes, Repurchase.
Does the business want to minimize changes? If yes, Rehost or Replatform (check for minor optimizations).
Does the business want to modernize? If yes, Refactor.
Is it a VMware environment? Consider Relocate.
Otherwise, Retain.
The 7 Rs are Rehost, Replatform, Refactor, Repurchase, Retire, Retain, and Relocate.
Rehost (lift and shift) moves applications as-is; it's fastest but may not reduce costs.
Replatform makes minor cloud optimizations, e.g., moving a database to Amazon RDS.
Refactor rewrites applications to be cloud-native using microservices and serverless.
Repurchase replaces an existing application with a SaaS product.
Retire decommissions applications that are no longer needed.
Retain keeps some applications on-premises due to compliance or technical reasons.
Relocate moves VMware workloads to VMware Cloud on AWS.
AWS Migration Hub and Application Discovery Service help assess and track migrations.
The exam tests scenario-based selection of the best migration strategy.
These come up on the exam all the time. Here's how to tell them apart.
Rehost (Lift and Shift)
Move as-is with no changes
Fastest migration path
Lowest risk of application breakage
Does not leverage cloud benefits like auto-scaling
Use tools like AWS SMS or CloudEndure
Replatform (Lift, Tinker, Shift)
Make minor cloud-optimized changes
Slightly slower than Rehost
Low risk but some changes require testing
Gains benefits like managed databases (RDS)
Use tools like AWS DMS for database migration
Refactor (Re-architect)
Rewrite application to be cloud-native
High effort and cost
Maximum long-term benefits (scalability, cost)
Retain control over code and data
Use microservices, serverless, containers
Repurchase (SaaS)
Replace with third-party SaaS product
Low effort, but vendor lock-in
Quick time-to-value
Lose control over customization
Examples: Salesforce, Workday
Mistake
Rehost is always the cheapest migration strategy.
Correct
Rehost can be cheaper initially because it requires less development, but it often results in higher ongoing costs because you are not using cloud-native features like auto-scaling or managed services. Over time, Refactor can be cheaper.
Mistake
Retain means you never migrate that application.
Correct
Retain means you postpone migration for now. You may revisit later when conditions change (e.g., regulatory approval, new technology).
Mistake
Refactor is the same as Replatform.
Correct
Refactor involves significant code changes to become cloud-native, while Replatform involves minimal changes like moving to a managed service. Refactor is much more effort.
Mistake
Repurchase is only for moving to AWS SaaS products.
Correct
Repurchase can involve any SaaS provider, not just AWS. For example, moving to Salesforce or Workday.
Mistake
All applications must be migrated during a cloud migration.
Correct
Some applications may be retained on-premises due to compliance, latency, or technical debt. Retain is a valid strategy.
The 7 Rs are Rehost, Replatform, Refactor, Repurchase, Retire, Retain, and Relocate. They represent different strategies for moving applications to the cloud, ranging from moving as-is (Rehost) to completely rewriting (Refactor). The exam expects you to know each definition and when to apply them.
Rehost (lift and shift) moves an application to the cloud with no changes. Replatform (lift, tinker, and shift) makes minor optimizations like moving a database to Amazon RDS. Replatform requires slightly more effort but yields better cloud benefits like managed backups. On the exam, look for keywords: 'as-is' for Rehost, 'minor changes' for Replatform.
Choose Refactor when you need to modernize the application to improve scalability, agility, or cost efficiency. It is best for monolithic applications that need to become microservices. Refactor requires significant development effort and is not suitable for quick migrations. The exam tests this: if the scenario mentions 'cloud-native' or 'modernize', Refactor is likely the answer.
Retain means keeping an application on-premises and not migrating it to the cloud at this time. Reasons include regulatory compliance, data residency requirements, or the application being too complex to migrate. It is a valid strategy, not a failure. The exam may present a scenario where retaining is the best option.
Relocate is often considered a separate R, specifically for moving VMware workloads to VMware Cloud on AWS. It is a variant of Rehost but specific to hypervisor-level migration. Some sources list 6 Rs excluding Relocate, but CLF-C02 typically includes it. On the exam, if you see 'VMware' in the scenario, Relocate may be the answer.
AWS provides AWS Application Discovery Service (for discovering on-premises infrastructure), AWS Migration Hub (central tracking), AWS Migration Evaluator (cost analysis), and AWS Server Migration Service (SMS) for server replication. CloudEndure Migration is also used for continuous replication. The exam may ask which tool to use for a specific task.
Typically, you choose one primary strategy per application. However, you might use Replatform for the database and Rehost for the web tier. The 7 Rs are applied at the application or workload level, not necessarily uniformly. The exam expects you to pick the best overall strategy.
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