Legacy to Cloud Modernization Playbook (Cloud Migration & Architecture)
- Practitioner
- Advanced
- Template Included
A practical playbook for deciding which legacy systems to rehost, replatform, refactor, or retire — and how to sequence the migration so cost, risk, and downtime stay manageable.
Should we always prefer refactor over rehost since it's "more cloud-native"?
No. Refactoring every application is the single most common way cloud migrations blow their budget. Reserve refactor effort for applications that are both business-critical and currently constrained by their architecture; rehost everything else and revisit later if the economics or performance don't hold up.
How do we handle applications tied to specialized on-premises hardware?
Classify them as Retain with an explicit re-evaluation date, and document the specific constraint (compliance, hardware dependency, vendor contract) driving that decision. Don't let "retain" become a silent default for anything that looks hard.
What's a realistic timeline for a 150-200 application estate?
Assessment and landing zone build typically take 4-6 weeks in parallel. Migration factory execution at a sustainable pace (8-15 applications per wave, monthly) usually takes 12-18 months to clear the full estate, with refactor-track applications running on a separate, longer timeline alongside it.
How do we avoid the classic post-migration cost overrun?
Build cost tagging and a showback dashboard into the landing zone before the first workload moves, and validate actual spend against baseline at the end of every wave — not at the end of the whole program, when it's too late to correct course cheaply.
Do we need a dedicated migration factory team, or can application teams migrate their own systems?
For estates larger than roughly 50 applications, a dedicated factory team with a repeatable runbook is faster and more consistent than distributed application-team-led migrations, which tend to reinvent the process each time and produce inconsistent landing zone usage.
Subscriber access
Unlock this playbook
This playbook — including every framework, template, and step-by-step section — is available free to Think Insights subscribers. Enter your email to unlock it instantly and get our weekly insights newsletter. No account needed, and access is remembered on this device.
