A company will run an application on Amazon EC2 instances continuously for one year. Which EC2 purchasing option is the most cost-effective for this steady, long-term use?

Reserved Instances (RIs) are the most cost-effective option for applications with steady-state, long-term usage (one year or more) because they offer significant discounts (up to 75%) compared to On-Demand pricing in exchange for a commitment to a specific instance type and region. Spot Instances are for fault-tolerant workloads that can tolerate interruptions, as they leverage unused EC2 capacity and can be terminated with short notice, making them unsuitable for continuous applications. On-Demand Instances are flexible but more expensive, ideal for short-term, irregular workloads where you don't want to commit. Dedicated Hosts provide dedicated physical servers for regulatory compliance or specific licensing requirements, but they are generally the most expensive option and not primarily for cost savings on steady-state applications.