For a steady production workload on Amazon EC2 that will run for one year, which instance purchasing option is the most cost-effective?

Reserved Instances (RIs) are the most cost-effective option for a steady production workload running for one year because they offer a significant discount (up to 75%) compared to On-Demand pricing in exchange for committing to a specific instance type and region for a 1- or 3-year term. Dedicated Hosts provide physical servers for your exclusive use, which is more expensive and typically used for specific licensing requirements, not general cost optimization. On-Demand Instances are flexible but more expensive, suitable for unpredictable workloads or short-term needs. Spot Instances offer the largest discounts but are interruptible, making them unsuitable for steady production workloads that require continuous availability.