A $50M+ ERP migration with a six-hour maintenance window. The risk is not in the cloud setup — it is in the data. This is the phased approach that keeps production running while the new environment is being built and validated alongside it.

• Phase 1 — build the target environment in parallel: cloud infra, patched OS, same app version as production
• Phase 2 — enable database log shipping or replication to keep the target near-current with production data
• Phase 3 — run full smoke tests against a data snapshot on the target; fix issues before cutover
• Cutover window: stop writes on source, let replication drain, flip DNS, start services on target in documented sequence
• Rollback plan must be as documented as the forward plan — test it before the cutover weekend
• Post-cutover: keep source warm for 72 hours; decommission only after business sign-off