How much outage time is involved in resizing an AWS RDS Multi-AZ instance?

Question

We're implementing new SQL Server databases in AWS. Our cloud engineer recommended RDS, despite the known downsides (inability to restore a single database or copy out a single backup, inability to resize the instance or reconfigure storage without downtime). Meanwhile, if we implement on EC2 we could get the benefit of zero-downtime upgrades.

In further reading, it seems like Multi-AZ may avoid downtime when resizing (see samples below) but the documentation is vague.

"Running a DB instance with high availability can enhance availability during planned system maintenance" https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Concepts.MultiAZ.html

"There is minimal downtime when you are scaling up on a Multi-AZ environment because the standby database gets upgraded first, then a failover will occur to the newly sized database." https://aws.amazon.com/blogs/database/scaling-your-amazon-rds-instance-vertically-and-horizontally/

My question: does using Multi-AZ in RDS allow zero downtime when adding storage? If not, how much outage time would we experience when reconfiguring a Multi-AZ instance?

Answer 1

Multi-AZ doesn't do zero downtime, but we generally see less than a minute (with MySQL).

I would just create a new multi-AZ db from a snapshot, and test it to see. It shouldn't cost more than a buck or two to find out.