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- The workbook uses Amazon's On-Demand pricing, which is the more expensive option for deploying EC2 and RDS instances. If your organization can make a 1- or 3-year commitment to particular compute instance types, discounts of roughly 30-40% are available when using Reserved Instances. So, costs can be reduced significantly.
- Secondly, the items involving usage (data transfer and load balancer units, mainly) are pretty much guesses. These values will vary, and typically grow larger, over time as more patrons use the service. This factor is somewhat true of compute instance sizes, as well. The costs illustrate a system where use has matured, rather than one initially deployed.
- The odd 334GB size of EBS volumes in large deployments is a suggested size to alleviate an I/O burst rate limit observed in database processing–higher EBS storage values result in higher I/O rate limits. Amazon docs suggests allocating 334GB for a 1000 IOPS base rate when operating a service with high database I/O requirements.
- At the time of this writing, recent code changes may reduce the performance needs for the scripting and database instances (as well as the higher I/O limit) when maintaining a large OverDrive collection. We'll keep watch and update the spreadsheet in three to four months if the reduction is verified in production.
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