Correct option is B
Option B: On-Demand instances are instances that can be launched and terminated at any time, and you pay only for the hours or minutes that you use them. They are cost-effective for short-term usage but do not provide any guarantee of availability beyond the underlying infrastructure's general availability. On-Demand instances do not require any upfront payment or long-term commitment, making them a flexible option for short-term usage.
Option C and D: Reserved instances are instances that you can reserve for a one-year or three-year term, providing you with a significant discount on the hourly rate. There are two types of Reserved instances, No Upfront costs Reserved and Partial Upfront costs Reserved, which require different payment structures upfront. They are more cost-effective than On-Demand instances for long-term usage, but they require upfront payment, and you commit to using them for a fixed term. Reserved instances offer availability guarantees, but they are not designed for short-term usage.
Option A: Spot instances allow you to bid for unused EC2 capacity and can offer significant cost savings compared to On-Demand and Reserved instances. However, the availability of spot instances is not guaranteed, and they can be terminated at any time with only two minutes' notice. Spot instances are an excellent option for workloads that can handle interruptions and have the ability to be restarted if the instance is terminated. Spot instances are not recommended for applications that require continuous availability and cannot tolerate interruptions.
Given the requirement of hosting a set of servers in the cloud for a short period of 3 months, the instances should be highly available and cost-effective, and the instances cannot be interrupted during processing, the best option would be On-Demand instances. On-Demand instances offer high availability without any upfront payment or long-term commitment, making them the most flexible and cost-effective option for short-term usage. Reserved instances are designed for long-term usage, and Spot instances cannot guarantee continuous availability, making On-Demand instances the best choice for this use case.
