Early attempts to move often look like a "Big Bang" approach. You turn off the application, copy the database, and turn it on in the new location.
Despite the best planning, migrations are "10x more difficult than people think". database migration
Smart companies choose a phased migration. They use to replicate data incrementally from the old house to the new one while people are still living in the old one. Early attempts to move often look like a "Big Bang" approach
The application is updated to write data to both the old and new databases simultaneously. This keeps the new system "warm" and up-to-date. Smart companies choose a phased migration
For a high-traffic app, "turning it off" for 4 hours costs millions in revenue and causes massive customer anger.
A dedicated "tiger team" tests every byte to ensure data integrity. Chapter 3: The Darkest Hour (When Things Go Wrong)