What Is a Blue-Green Database Migration?
A blue-green database migration maintains a current and a target database state in parallel, replicating changes between them, so a cutover can switch the application to the new one quickly. If the new state misbehaves, traffic can switch back to the original. It applies the blue-green release idea to data, where copying and reconciling state is harder than for stateless services.
Why it matters
Schema changes are among the riskiest deploys because they are hard to reverse once data is written. Running two synchronized states gives a fast, low-risk cutover and a viable rollback path.
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