Why?

• Save money
• Reserve capacity

Types

Reserved Instances

• Standard Reserved Instances
  • Apply to a single instance family, platform, scope, and tenancy over a term
  • One or three year term
  • Can reserve capacity (locked into one availability zone, "zonal RI") or be regional (can launch in any AZ within the region, "regional RI")
  • Greatest discount

• Convertible Reserved Instances
  
  • They allow you to change the instance family and other parameters associated with a Reserved Instance at any time. For example, you can convert C3 RIs to C4 RIs to take advantage of a newer instance type, or convert C4 RIs to M4 RIs if your application turns out to need more memory.
  • Three year term
  • Can reserve capacity (locked into one availability zone) or be regional (can launch in any AZ within the region)
  • Slightly more expensive than standard

Scheduled Instances

• One year term
• Repeating schedule (daily, weekly, monthly)
• http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-scheduled-instances.html

Tenancy

• If you're using dedicated instances, choose Dedicated Tenancy
• If not, choose Default Tenancy

Usage

Instance Size Flexibility

• All Regional Linux/UNIX RIs with shared tenancy now apply to all sizes of instances within an instance family and AWS region, even if you are using them across multiple accounts via Consolidated Billing.
• RIs with Instance Size Flexibility use a concept of normalized units to apply billing credits.

• Let’s say you already own an RI for a c4.8xlarge (normalization factor of 64). This RI now applies to any usage of a Linux/UNIX C4 instance with shared tenancy in the region. This could be:

  • One c4.8xlarge instance.
  • Two c4.4xlarge (normalization factor of 32 each) instances (64 total).
  • Four c4.2xlarge (normalization factor of 16 each) instances (64 total).
  • Sixteen c4.large (normalization factor of 4 each) instances (64 total).
  • It also includes other combinations such as one c4.4xlarge and eight c4.large instances.
• If you own an RI that has a smaller normalization factor than the instance that you are running, you will be charged the pro-rated, On-Demand price for the excess.

• If you own an RI for a large instance and run a smaller instance, the RI price will apply to the smaller instance. However, the unused portion of the reservation will not accumulate.

  Instance size flexibility does not apply to Windows, Windows with SQL Standard, Windows with SQL Server Enterprise, Windows with SQL Server Web, RHEL, and SLES Reserved Instances.

Guaranteed Capacity

• If an Availability Zone is specified, EC2 reserves capacity matching the attributes of the RI. The capacity reservation of an RI is automatically utilized by running instances matching these attributes.
  

Payment Options

• All up front
  • Biggest discount
• Partial up front
• No up front
  • One year term
  • Available with a 3 year term for C4, M4, R4, I3, P2, X1, and T2 Standard Reserved Instances only