A company is moving an on-premises server to an Amazon EC2 instance. The server must run continuously for the next 12 months. Which EC2 pricing model is the most cost-effective for this workload?

Reserved Instances (RIs) are the most cost-effective option for a server that must run continuously for a predictable duration, like 12 months. RIs offer a significant discount (up to 75%) compared to On-Demand pricing in exchange for a commitment to a specific instance type and region for a 1- or 3-year term. On-Demand instances are more expensive as they offer flexibility without a long-term commitment. Dedicated Hosts provide physical servers for your exclusive use, which is overkill and more expensive if only an EC2 instance is needed. Spot Instances are the cheapest but are suitable only for fault-tolerant workloads that can tolerate interruptions, as AWS can terminate them with short notice, making them unsuitable for a continuously running server.