---
title: "Migration and modernization"
chapter: "11"
---

# Migration and modernization

Migration is a business change carried by technology.

## Discover first

Inventory applications, owners, dependencies, data, contracts, usage, costs,
and risk. Use Migration Hub and discovery tooling where appropriate. Group
systems into waves that produce value and keep dependencies manageable.

## The migration choices

- **Retire:** remove what no longer provides value.
- **Retain:** keep it for now.
- **Rehost:** move with minimal change.
- **Relocate:** move a platform with little application change.
- **Replatform:** use some managed capabilities without rewriting everything.
- **Repurchase:** replace with a product or SaaS.
- **Refactor:** redesign for cloud-native capabilities.

Choose per workload. A company-wide “refactor everything” program usually
creates too much simultaneous risk.

## Useful services

Application Migration Service (MGN) supports rehosting servers. Database
Migration Service (DMS) moves supported databases and can replicate changes.
DataSync moves file/object data. Storage Gateway connects on-premises workflows
to cloud storage. Snow Family supports some offline/edge transfer cases.

## Safe wave pattern

1. Build the landing zone and connectivity.
2. Pilot a representative low-risk workload.
3. Prove security, operations, backup, and rollback.
4. Migrate bounded waves.
5. Validate business data and performance.
6. Cut over with explicit go/no-go criteria.
7. Decommission only after reconciliation and retention obligations.

## Modernization rule

Modernize where it changes an important outcome: faster releases, lower
operational burden, better scale, or lower risk. Do not rewrite a stable system
only to make the diagram look newer.