Two Environments
A blue green cutover runs two database environments side by side. Blue is the current live system; green is the new one, kept in sync by replication. The cutover flips traffic from blue to green as a single controlled action.
The Cutover Steps
- Keep green replicating from blue until lag is near zero.
- Briefly stop writes to blue, often a few seconds, so green can fully catch up.
- Redirect the application to green and resume writes.
The brief write pause guarantees green has every committed change before it becomes authoritative, avoiding lost writes.
Fast Rollback
The big advantage is a clean rollback path. If green misbehaves right after cutover, you switch traffic back to blue, which is still intact. To make rollback safe, many setups configure reverse replication from green to blue during the switch, so blue stays current and can take over again if needed.
Key idea
A blue green data cutover keeps a synced green database alongside live blue, pauses writes briefly to flip traffic, and uses reverse replication so rollback to blue stays safe.