Part 8: Phase 3 — Full Cutover & Decommissioning the Monolith
← Previous Chapter: Part 7: Phase 2 — Dual-Write | Series Hub | Next Chapter: Part 9: Transactional Outbox & Sagas → Answer-first: Phase 3 transfers write authority for Orders and Payments to the Go microservices. Once historical orders are reconciled and payment webhooks are repointed, the Magento PHP monolith is placed in read-only maintenance mode and subsequently decommissioned. The Cutover Runbook Checklist: T-24h: Run full data reconciliation audit between MySQL and PostgreSQL. T-2h: Lower DNS TTL to 60 seconds on all retail domains. T-0: Flip Cloudflare routing rule for /checkout to Go order-service. T+1h: Verify zero failed payments in Stripe / PayPal webhooks. T+48h: Terminate legacy Magento EC2 instances.