AWS Migration Strategies: The 6 Rs
Migrating to AWS is not a monolithic process. Depending on business goals, technical debt, and time constraints, organizations choose different paths. For the SAA-C03 exam, you must identify the most efficient migration strategy based on specific scenario requirements.
The “Moving House” Analogy
Imagine you are moving from an old house (On-Premises) to a modern luxury apartment (AWS):
- Rehosting: You hire a truck and move all your old furniture exactly as it is. It’s fast, but your old bulky sofa might not fit the new aesthetic.
- Replatforming: You move your furniture, but you buy a new, energy-efficient fridge that fits the apartment’s pre-installed kitchen hookups.
- Refactoring: You realize your old furniture doesn’t work. You buy modular, smart furniture designed specifically for the apartment layout.
- Repurchasing: You sell everything and move into a fully furnished apartment where the landlord provides all services (SaaS).
- Retaining: You keep a few boxes in the old house’s garage because they aren’t ready to move yet.
- Retiring: You finally throw away that broken chair you haven’t used in 10 years.
Core Concepts & Well-Architected Alignment
Migration strategies directly impact the AWS Well-Architected Framework pillars:
- Performance Efficiency: Refactoring allows for serverless and auto-scaling, maximizing performance.
- Operational Excellence: Replatforming to managed services (like RDS) reduces the operational burden of patching and backups.
- Cost Optimization: Retiring unused assets immediately lowers the TCO (Total Cost of Ownership).
Migration Strategy Comparison
| Strategy | Complexity | Cloud Benefit | Common Tools |
|---|---|---|---|
| Rehost (Lift & Shift) | Low | Low (Immediate) | AWS Application Migration Service (MGN) |
| Replatform (Lift & Reshape) | Medium | Medium | AWS Database Migration Service (DMS) |
| Refactor (Decouple) | High | Highest (Cloud Native) | AWS Lambda, Fargate, SQS |
| Repurchase (Drop & Shop) | Low/Medium | High (SaaS) | AWS Marketplace |
Decision Matrix (If/Then)
- If the requirement is to move quickly with zero code changes: Use Rehost.
- If you want to reduce DB management but keep the app logic: Use Replatform.
- If the legacy app is a “monolith” requiring high scalability: Use Refactor.
- If you are moving from a self-hosted CRM to Salesforce: Use Repurchase.
- If an application has strict compliance requirements that AWS can’t meet yet: Use Retain.
Exam Tips: Golden Nuggets
- MGN is the “Go-To”: AWS Application Migration Service (MGN) is the primary recommendation for Rehosting physical, virtual, or cloud-based servers.
- Managed Services: Look for keywords like “reduce administrative overhead.” This almost always points to Replatforming (e.g., moving from on-prem SQL Server to Amazon RDS).
- VMware Cloud on AWS: If the scenario mentions a large VMware environment and a “fast” migration without changing VM formats, this is a specialized Rehosting path.
- Refactoring = Agility: If the goal is “maximum business agility” or “innovation,” Refactoring (Cloud-Native) is the answer, despite the high effort.
Migration Visual Roadmap
Key Services
- AWS MGN: Automated lift-and-shift server migration.
- AWS DMS: Migrates databases with minimal downtime.
- SCT: Schema Conversion Tool for heterogeneous DB moves.
Common Pitfalls
- Over-Engineering: Trying to refactor everything at once (causes delay).
- Ignoring Egress: Not accounting for data transfer costs out of AWS.
- Licensing: Forgetting to check if MSFT/Oracle licenses are portable (BYOL).
Quick Patterns
- Speed: Rehost + MGN.
- DB Modernization: Replatform + DMS.
- Legacy Replacement: Repurchase (SaaS).