Cloud Migration Strategies
Understand the benefits of and strategies for migrating to the AWS Cloud
What you will learn
- Name the six migration strategies and explain the fundamental difference between them.
- Distinguish Replatform from Refactor — the most commonly confused pair on the exam.
- Match each strategy to a realistic business scenario that fits it.
- Recall that the first phase of any migration is assessment, not immediate transfer.
"Migrating to the cloud" is not one single action — it's a spectrum of options that differ in how deeply the legacy application is modified. Picking the wrong strategy either wastes time on a re-architecture the business doesn't need yet, or carries the legacy system's problems over unchanged after a literal move.
The six strategies (6 R's)
| Rehost | Moving the application largely as-is with no fundamental code change — the fastest, also known as "lift-and-shift." |
|---|---|
| Replatform | Limited changes (like swapping a self-managed database for managed RDS) without rewriting the application's architecture. |
| Repurchase | Abandoning the old system entirely and switching to a ready-made SaaS product serving the same function. |
| Refactor / Re-architect | Rewriting the application with cloud-native architecture (like splitting it into microservices) to fully exploit the cloud's advantages. |
| Retire | Shutting the application down permanently because it's no longer needed — not migrated at all. |
| Retain | Keeping the application on-premises as-is for now, for compliance or technical-complexity reasons, with possible later migration. |
AWS's three migration phases
Assess
Inventory existing applications and estimate their cloud readiness before any actual move.
Mobilize
Build the detailed migration plan and prepare the foundational infrastructure and required skills.
Migrate & Modernize
Execute the actual migration of each application per its chosen strategy.
Rehost vs. Refactor
| Rehost | Refactor | |
|---|---|---|
| Speed | The fastest of the six strategies | The slowest — requires actual rewriting |
| Exploiting cloud advantages | Limited immediately after the move | Full — purpose-built for a cloud environment |
What matters on the exam
- "Without modifying the code" in a question's wording always points to Rehost.
- "Replacing with a ready-made SaaS product" points to Repurchase, not Replatform.
Replatform is not Refactor
Both modify the legacy system, but the difference is depth: Replatform is a limited, targeted change (like swapping a database) without touching the application's architecture, while Refactor is a fundamental rewrite to fully exploit cloud-native features.
Quick check
Answer in your head first, then reveal.
Which of the six migration strategies is fastest?Reveal the answer
Rehost.
Which strategy fits an application no longer used at all?Reveal the answer
Retire.
What is the first of AWS's three migration phases?Reveal the answer
Assess.
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Your next step
Read the lesson, then mark it complete
Sources
Used to verify the facts. The writing is original to Passuit.