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Platform Migration Checklist: How to Switch Without Downtime
A successful platform migration requires four phases: discovery (2 weeks), parallel build (4–8 weeks), controlled cutover (1 week), and stabilisation (2 weeks). The key to zero-downtime migration is running both systems in parallel, with a rollback plan at every stage. Most migration failures come from skipping the parallel phase.
Platform migrations are the most underestimated projects in technology. A migration that 'should take 4 weeks' routinely takes 12. The reason: every migration surfaces hidden complexity. Data that looked clean has edge cases. Integrations you forgot about break. Team workflows change in ways nobody anticipated.
Phase 1: Discovery (2 weeks). Audit everything: data schemas, integrations, automations, user workflows, permissions, and edge cases. Document what the current system does, not what it was designed to do — these are often different. Map every integration, including the ones that 'just work' and nobody thinks about.
Phase 2: Parallel Build (4–8 weeks). Build the new system alongside the old one. Import data, configure integrations, and set up automations. Run both systems simultaneously. Compare outputs. When they match consistently, you're ready for cutover. This is the phase people skip. Don't skip it.
Phase 3: Controlled Cutover (1 week). Switch a small group of users first (canary release). Monitor for issues. Expand gradually. Keep the old system running in read-only mode. Have a documented rollback plan that can be executed in under 30 minutes.
Phase 4: Stabilisation (2 weeks). Monitor everything intensively. Fix issues as they surface. Gather user feedback. The first two weeks after cutover will reveal problems that testing didn't catch. Budget time for this explicitly.
The most dangerous words in a migration: 'We'll figure it out during cutover.' Every decision should be made before cutover weekend. Every script should be tested. Every rollback path should be documented and rehearsed.
Frequently Asked Questions
8–16 weeks for a standard business application (CRM, project management, ERP). Complex migrations with multiple integrations and large datasets can take 3–6 months. The discovery phase should give you a reliable estimate. Distrust any estimate made before discovery.
Yes, with proper planning. The parallel-run phase catches data mapping issues before cutover. Incremental sync (rather than big-bang data dumps) ensures data stays current in both systems. Always maintain a rollback capability for at least 30 days post-cutover.
Phased migration is almost always safer. Migrate one department, one data type, or one workflow at a time. This contains blast radius, builds team confidence, and lets you apply lessons from each phase to the next. Big-bang migrations are appropriate only when the systems are too tightly coupled to separate.
Sources
- Google Cloud: Migration Planning(accessed 2026-01-18)
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