SRIs: Save On Reserved Instances By Purchasing On A Schedule
By: Date: Categories: AWS Cloud

Late last week AWS announced the launch of Scheduled Reserved Instances (SRIs), a new way to reserve capacity on a recurring, pre-determined basis. SRIs allow AWS users to create a daily, weekly, or monthly schedule over the course of a one-year term. After completing the SRI purchase, the instances are available to launch during the specified time windows.


SRIs will be a useful addition to the toolkit of AWS users working with Reserved Instances, offering additional savings for those users able to purchase RI capacity on a determinable schedule. Much like optimized use of RIs, SRIs represent an opportunity for increased flexibility and cost savings for sophisticated AWS users with predictable workloads.


AWS sets out the following common use cases for Scheduled Reserved Instance purchases:

  • A bank or mutual fund performs Value at Risk calculations every weekday afternoon.
  • A phone company does a multi-day bill calculation run at the start of each month.
  • A trucking company optimizes routes and shipments on Monday, Wednesday, and Friday mornings.
  • An animation studio performs a detailed, compute-intensive 3D rendering every night.


Scheduled Reserved Instances

With this launch, Amazon Web Services customers in selected regions will be able to access two types of Reserved Instances:

Standard Reserved Instance: The new name for the original Reserved Instance, this model allows users to purchase reserved EC2 compute capacity for a one or three year term, to be used at any time.

Scheduled Reserved Instance: The new Scheduled Reserved Instance model allows for the purchase of reserved instances for predefined blocks of time, on a recurring basis, for a one-year term. AWS has promised prices in the range of 5-10% lower than the equivalent On-Demand rates.


Purchasing a Reserved Instance means making a commitment to an upfront cost and/or an ongoing hourly rate for a certain number of EC2 instances/servers of a certain type. In exchange, if you are running the same number of EC2 instances/servers of the matching (‘applicable’) type, instead of being charged the full standard hourly rate amount for those instances, you will be charged only the (discounted) costs of the Reserved Instance.


The new functionality is currently only available in the US East (Northern Virginia), US West (Oregon), and Europe (Ireland) regions, with support for the C3, C4, M4, and R3 instance types. AWS is yet to announce an exact date for deployment beyond these regions.


The increased flexibility from SRI introduces some additional complexity for users seeking to take advantage. The next major release of the CloudMGR RI Tool will feature an update to integrate and support the functionality of Scheduled Reserved Instances. The improved RI will make it possible to get the full benefits of SRI with the minimum possible level of additional user input and complexity.

Subscribe to the blog for our pre-release announcement in the coming weeks.

You can read AWS’ full release blog post here.

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