To prevent Amazon RDS for PostgreSQL Multi-AZ DB instances from running low on disk space, enabling storage auto-scaling is the most straightforward solution. This feature automatically adjusts the storage capacity of the DB instance when it approaches its limit, thus preventing the database from running out of space and triggering CloudWatch alarms. Option C is the least intrusive and most effective solution as it only requires a modification to the existing CloudFormation template to enable auto-scaling on storage. For reference, see AWS documentation on managing RDS storage automatically Managing RDS Storage Automatically.