Migration: The 7 Rs, TCO & Waves

Migration: The 7 Rs, TCO & Waves

Step 1 of 12

apps12before/yr84

Twelve applications cost 84 units a year on premises (illustrative units). Each gets exactly one of seven Rs.

The Idea

Every application gets one of seven strategies: retire, retain, rehost (lift and shift), relocate (to the cloud version of its platform), repurchase (often SaaS), replatform (a few changes, such as a managed database) or refactor (re-architect, the costliest). TCO adds years of running cost to the one-time cost of moving. Wave planning groups hard dependencies into move groups and starts with small, low-complexity waves.

Real-World Example

Twelve applications cost 84 units a year (illustrative). After sorting them into the 7 Rs they cost 58 a year plus 30 once: 204 over three years against 252 for staying, breaking even after about 14 months.

The Tradeoff

Rehosting is fast but leaves savings for later, while refactoring during the move multiplies risk. Retain is a valid answer, not a failure.

Hands-On

# illustrative units per year: (before, after, one-time)
plan = {"retire": (6, 0, 1), "retain": (10, 10, 0), "rehost": (24, 18, 6),
        "relocate": (12, 10, 2), "repurchase": (8, 6, 3),
        "replatform": (14, 9, 6), "refactor": (10, 5, 12)}
years = 3
stay = sum(b for b, _, _ in plan.values()) * years
move = sum(a * years + once for _, a, once in plan.values())
print(stay, move)  # 252 204

Your turn

Put the steps in the right order.

1. 1Group applications with hard dependencies into move groups↑↓
2. 2Collect the inventory and map dependencies↑↓
3. 3Migrate a small first wave of low-complexity applications↑↓
4. 4Assign one of the 7 Rs to each application↑↓

Check order

Mini quiz

1 / 3

A SQL Server database moves to Amazon RDS for SQL Server with no application rewrite. Which strategy is that?

• ARehost
• BReplatform
• CRefactor
• DRepurchase

Sources

• About the migration strategies — AWS Prescriptive Guidance
• Task 5: Defining the wave planning process — AWS Prescriptive Guidance
• Wave planning — AWS Prescriptive Guidance