Question 751 - SAP-C01 discussion

For Amazon Web Services, the reserved instance (standard or convertible) helps the user save money if the user is going to run the same instance for a longer period. Generally, if the user uses the instances around 30-40% of the year annually it is recommended to use RI. Here as the instance runs only for 1 hour 50 minutes daily, or less than 8 percent of the year, it is not recommended to have RI as it will be costlier. At its highest potential savings, you are still paying 25 percent of an annual cost for a reserved instance you are you using less than 2 hours a day, (or less than 8 percent of each year) you are not saving money. Even a scheduled reserved instance has a key limitation, which is that it cannot be stopped or rebooted, only manually terminated with a possibility that it could be restarted. You would have to terminate and restart it within the 1 hour 50-minute window, otherwise you would need to wait until the next day. For a critical daily process, this is likely not an option. Spot Instances are not ideal because the process is critical, and must run for a fixed length of time at a fixed time of day. Spot instances would stop and start based on fluctuations in instance pricing, leaving this process potentially unfinished.

The user should use on-demand with EBS in this case. While it has the highest cost, it also has the greatest flexibility to ensure that a critical process like this is always completed.

Reference: http://aws.amazon.com/ec2/purchasing-options/reserved-instances/