AWS Architecture Guide

Migration and Modernization Decisions

What This Chapter Is About

Teach migration as a structured program of assessment, dependency mapping, landing-zone readiness, migration waves, modernization choices, and operating-model change rather than as a one-time copy exercise.

Keep one durable idea in view:

Strong AWS migration design starts by deciding what should move, how fast it should move, and which changes should wait until the new operating model is stable.

Sections

  1. Migration Decision Mental Model

  2. Assess, Discover, and Plan Migration Waves

  3. Choosing Among the 7Rs and Where to Modernize

  4. AWS Migration Services, Cutover, and Validation

  5. Enterprise Migration Program Scenario

How the Chapter Develops

The chapter develops in this order:

  1. Start with migration as a business and operating-model decision, not a tooling exercise.

  2. Show how discovery, dependency mapping, and wave planning reduce hidden risk before large moves begin.

  3. Explain how the 7Rs create different modernization paths for different applications.

  4. Connect the decision model to AWS migration tooling, cutover choices, rollback planning, and validation.

  5. Apply the full model to a phased enterprise migration program with realistic trade-offs.

Together, these sections show that AWS migration is about sequencing risk, ownership, and modernization timing, not just moving servers into a new environment.

What You Will Be Able to Do

By the end of this chapter, the reader should be able to:

  • Explain why migration strategy begins with portfolio and dependency understanding.

  • Choose between rehost, replatform, refactor, retain, retire, repurchase, and relocate in practical terms.

  • Describe where AWS migration tooling fits into discovery, execution, and cutover.

  • Separate near-term migration goals from later modernization goals when time or risk is constrained.

  • Walk through a phased migration approach for a multi-application estate.

Key Ideas

  • Migration is a program of business change, architecture change, and operational change.

  • The 7Rs are portfolio decision patterns, not slogans to memorize in isolation.

  • Dependency mapping and wave planning matter because application moves are rarely independent.

  • AWS migration tools help execute decisions, but they do not replace migration strategy.

  • The best modernization timing is often after stability, observability, and ownership are established in AWS.