我们可以使用云形成模板将RDS只读副本提升为主吗？

Question

我们可以使用控制台和 CLI 轻松提升 RDS 只读副本，但是有没有办法让主访问意味着使用云形成提升主访问？

Answer 1

CloudFormation uses the property "SourceDBInstanceIdentifier" to determine whether a DBInstance is a read replica or not. If this property has any non-empty value, the DBInstance will be created as a read replica.

If you remove this property once a read replica is created and update your CloudFormation stack, a new DBInstance will be created that won't be a read replica, it will be it's own standalone database. However, the new standalone database will not have the contents of the read replica.

The solution to this will be to regularly back up your read replica. When you want to promote your read replica, remove "SourceDBInstanceIdentifier" and set "DBSnapshotIdentifier" to the most recent snapshot of the read replica. This should effectively promote your read replica to master with most the data still intact

Answer 2

The RDS standby replica (multi-az) will automatically be switched to master in case of failures on the master node.

How you setup the multi-az replica (could be through cloudformation) will determine the automatic switch over. Please note that the standby replica becomes the master only when there is an AZ outage, primary instance fail, software patching and not when there is scenarios of locks or database level operation timeouts.