You should thoroughly test any upgrade before applying it to your production instances.
We don’t automatically upgrade an Amazon RDS DB instance until we post an announcement to the forums announcement page and send a customer e-mail notification.
Even though upgrades take place during the instance maintenance window, we still schedule them at specific times through the year.
We schedule them so you can plan around them, because downtime is required to upgrade a DB engine version, even for Multi-AZ instances.
Amazon RDS takes two DB snapshots during the upgrade process.
You can choose to upgrade a DB instance in some cases when a new DB engine version is supported by Amazon RDS.
Database version upgrades consist of major and minor version upgrades.Major database version upgrades can contain changes that are not backward-compatible with existing applications.As a result, Amazon Relational Database Service (Amazon RDS) doesn't apply major version upgrades automatically; you must manually modify your DB instance.The first DB snapshot is of the DB instance before any upgrade changes have been made.If the upgrade doesn't work for your databases, you can restore this snapshot to create a DB instance running the old version.The second DB snapshot is taken when the upgrade completes.