Zero Downtime Cloud Migration: The 6-Phase Playbook

Phase 1 is never 'lift and shift.' Here's the framework that keeps production stable throughout the entire move. After leading migrations for organizations ranging from 200 to 4,000 engineers, I've distilled it into 6 phases that keep production alive and teams sane. Phase 1: Discovery & Dependency Mapping Before touching a single VM, audit everything. Inventory all services: apps, databases, middleware, integrations Map inter service dependencies including the undocumented ones (ask the engineers who've been there longest) Tag everything by criticality, data sensitivity, migration complexity Identify the "spiders in the web" services everything else depends on Tools: AWS Application Discovery Service, Cloudamize, or a structured spreadsheet + interviews. Phase 2: Cloud Foundation & Landing Zone Build the platform before you migrate anything. Set up your VPC architecture (hub spoke or flat decide now) Implement IAM roles, SCPs, and guardrails Deploy centralized logging, monitoring, and