Amazon Relational Database Service
User Guide (API Version 2013-09-09)
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Working with Reserved DB Instances

Things You Should Know About Reserved DB Instances

Reserved DB instances let you make a one-time up-front payment for a DB instance and reserve the DB instance for a one- or three-year term at significantly lower rates. You can use the command line tools, the API, or the AWS Management Console to list and purchase available Reserved DB instance offerings.

Reserved Instances are available in three varieties—Heavy Utilization, Medium Utilization, and Light Utilization—that enable you to optimize your Amazon RDS costs based on your expected utilization. For more information about reserved instance types, see Amazon RDS Reserved Instances.

Heavy Utilization Reserved DB instances enable workloads that have a consistent baseline of capacity or run steady-state workloads. Heavy Utilization Reserved DB instances require the highest up-front commitment, but if you plan to run more than 79 percent of the Reserved DB instance term you can earn the largest savings (up to 58 percent off of the On-Demand price). Unlike the other Reserved DB instances, with Heavy Utilization Reserved DB instances, you pay a one-time fee, followed by a lower hourly fee for the duration of the term regardless of whether or not your DB instance is running.

Medium Utilization Reserved DB instances are the best option if you plan to leverage your Reserved DB instances a substantial amount of the time, but want either a lower one-time fee or the flexibility to stop paying for your DB instance when you shut it off. This offering type is equivalent to the Reserved DB instance offering available before the 2011-12-19 API version of Amazon RDS. Medium Utilization Reserved DB instances are a more cost-effective option when you plan to run more than 40 percent of the Reserved Instance term. This option can save you up to 49 percent off of the On-Demand price. With Medium Utilization Reserved DB instances, you pay a slightly higher one-time fee than with Light Utilization Reserved DB instances, and you receive lower hourly usage rates when you run a DB instance.

Light Utilization Reserved DB instances are ideal for periodic workloads that run only a couple of hours a day or a few days per week. Using Light Utilization Reserved DB instances, you pay a one-time fee followed by a discounted hourly usage fee when your DB instance is running. You can start saving when your instance is running more than 17 percent of the Reserved DB instance term, and you can save up to 33 percent off of the On-Demand rates over the entire term of your Reserved DB instance.

Remember that discounted usage fees for Reserved Instance purchases are tied to instance type and Availability Zone. If you shut down a running DB instance on which you have been getting a discounted rate as a result of a Reserved DB instance purchase, and the term of the Reserved DB instance has not yet expired, you will continue to get the discounted rate if you launch another DB instance with the same specifications during the term. Your up-front payment for a reserved instance will reserve the resources for your use; since these resources are reserved for you, you will be billed for the resources regardless of if you use them.

The following table summarizes the differences between the Reserved DB instances offering types.

Reserved Instance Offerings

OfferingUpfront CostUsage FeeAdvantage

Heavy Utilization

Highest

Lowest hourly fee. Applied to the whole term whether or not you're using the Reserved DB instance.

Lowest overall cost if you plan to utilize your Reserved DB instances more than 79 percent of a 3-year term.

Medium Utilization

Average

Hourly usage fee charged for each hour you use the DB instance.

Suitable for elastic workloads or when you expect moderate usage, more than 40 percent of a 3-year term.

Light Utilization

Lowest

Hourly usage fee charged. Highest fees of all the offering types, but they apply only when you're using the Reserved DB instance.

Highest overall cost if you plan to run all of the time, however lowest overall cost if you anticipate you will use your Reserved DB instances infrequently, more than about 15 percent of a 3-year term.