Migration Implementation, Cutover, and Validation
Domain scope
This domain tests implementation, cutover, and validation: runbooks, rehearsal, freeze periods, DNS and traffic switching, smoke tests, hypercare, and rollback. The exam rewards controlled change over heroic execution.
Core rules
- Write a cutover runbook with timestamps, owners, commands, verification steps, communication points, and rollback triggers. Rehearse it at least once on a production-like copy.
- Freeze code and configuration changes before cutover. Confirm backups, replication lag, certificates, DNS TTL, and access approvals.
- Switch traffic in controlled stages: canary or small cohort, then broader. Validate technical, business, and security checks, not only login.
- Define rollback authority and the point of no return in advance. Rollback must be tested, not just documented.
- Run hypercare with elevated monitoring, daily triage, and clear exit criteria such as stable error rate, latency, and no severity-1 incidents for an agreed period.
Worked example
An e-commerce platform cuts over on a Saturday night. DNS TTL was lowered to 60 seconds three days earlier. The runbook freezes deployments at 18:00, stops writes, drains replication, switches the database connection, updates DNS weighted records to 10% of traffic, and runs smoke tests for search, cart, checkout, and refund. After 30 minutes of stable error rate and checkout latency, traffic moves to 100%. Rollback triggers include checkout failure above 2% or replication lag above five minutes before the point of no return. Hypercare lasts five business days.
Traps
No rehearsal; leaving a long DNS TTL; validating only infrastructure health; allowing changes during the freeze; and declaring success before business reconciliation and hypercare exit.