On-Demand Instances are the most cost-efficient pricing model for an uninterruptible workload that runs once a year for 24 hours. On-Demand Instances let you pay for compute capacity by the hour or second, depending on which instances you run. No long-term commitments or up-front payments are required. You can increase or decrease your compute capacity to meet the demands of your application and only pay the specified hourly rates for the instance you use1. This model is suitable for developing/testing applications with short-term or unpredictable workloads2. The other pricing models are not cost-efficient for this use case. Reserved Instances and Savings Plans require a commitment to a consistent amount of usage, in USD per hour, for a term of 1 or 3 years. They provide significant discounts compared to On-Demand Instances, but they are not flexible or scalable for workloads that run only once a year12. Spot Instances are the cheapest option, but they are not suitable for uninterruptible workloads, as they can be reclaimed by AWS at any time. They are recommended for applications that have flexible start and end times, or that are only feasible at very low compute prices12. Dedicated Instances are designed for compliance and licensing requirements, not for cost optimization. They are more expensive than the other options, as they run on single-tenant hardware12. References: Amazon EC2 – Secure and resizable compute capacity – AWS, Amazon EC2 - How AWS Pricing Works