AWS is now letting Amazon Aurora and Amazon RDS customers reserve DB instance capacity ahead of time, so a launch, migration or disaster recovery doesn’t stall because a zone ran out of instances.

On-Demand Capacity Reservations for the two database services went live Wednesday in all AWS commercial Regions. Customers choose a DB instance class, engine, Availability Zones and the amount of capacity per zone, and RDS holds it. The goal, AWS said, is to make sure create, restore, scale-compute and start operations “don’t fail because of insufficient capacity.”

AWS listed migrations, product launches, seasonal peaks, high-availability deployments and disaster recovery as the target cases. Reservations can span two or more Availability Zones to back Multi-AZ setups, and a reservation is used by referencing it when creating, restoring, modifying or starting a DB instance.

There are two ways to book. Capacity for immediate use carries no commitment and can be canceled at any time.…