What Are the Differences Between Yearly/Monthly and Pay-per-Use Billing Modes?

Yearly/Monthly is a prepaid mode. If your future usage is predictable, this billing mode is generally less expensive than pay-per-use. Longer subscriptions offer larger discounts.

Pay-per-use is a postpaid mode. You are only billed for how long you have actually used your instance. This mode can be a good option when future requirements are unpredictable. Pay-per-use instances are priced by the hour, but if an instance is used for less than one hour, you will be billed based on the actual duration.