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Mechanical Turk requestor accounts can use the same email address and password as AWS root accounts. However, in order to keep these concerns seperate, we recommend using different accounts for each of AWS, Amazon store, and Mechanical Turk.
RDS
How is the OS hosting my RDS patched?
RDS is a fully-managed service at Amazon, meaning you do not have access to the underlying operating system. Patching to the database engine or underlying operating system is handled as a scheduled maintenance event:
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_UpgradeDBInstance.Maintenance.html
Maintenance to RDS can happen "immediately" or in a regularly-scheduled 30-minute window. An RDS instance can also be configured to automatically apply "minor" updates during the standing maintenance window without prior approval. For instances supported by the CIT DBA team, they can likely give you the details on your current configuration(s); the Cloud Team can also help fill in gaps if needed.
It is certainly likely that this activity will result in a brief outage. Use of a Multi-AZ deployment for RDS helps mitigate that for most activities since AWS will first perform maintenance on the standby instance, promote that to primary, then perform maintenance on the "old primary/new standby". Emphasis is on "most" because some major changes, like modifying the database engine, may require updating both primary and standby at the same time. Multi-AZ also gives you increased availability in the case of an Availability Zone going offline. Keep in mind that Multi-AZ deployments come with additional cost. You will need to find the balance between desired availability and total monthly spend.