Are OpenSearch Reserved Instances automatically applied to running on-demand OpenSearch instances?

Question

Hi AWS community,
I have a question about OpenSearch Reserved Instances. I want to purchase an OpenSearch Reserved Instance to save on costs for my OpenSearch workloads. However, I'm not sure if this Reserved Instance is automatically applied to my future on-demand OpenSearch instances.
Can anyone confirm if OpenSearch Reserved Instances are automatically applied to running on-demand instances, or do I need to manually associate them with my running instances after creating the domain with on-demand?
Also, are there any specific steps or considerations I need to keep in mind when associating Reserved Instances with running instances?
Thank you in advance for your help!

Rajat_C · Answer

Hello,

Once you have purchased a reserved instance, your OpenSearch domain using same instance type will start getting billing discounts without any changes in OpenSearch domain.

Amazon OpenSearch RIs are not flexible; they only apply to the exact instance type that you reserve. For example, a reservation for eight `c5.2xlarge.search` instances does not apply to sixteen `c5.xlarge.search` instances or four `c5.4xlarge.search` instances.

Note: OpenSearch reserved instances are different from EC2 reserved instances and are purchased from AWS OpenSearch console/CLI/SDK. Please refer to below document for reference.

[+] Reserved Instances in Amazon OpenSearch Service - https://docs.aws.amazon.com/opensearch-service/latest/developerguide/ri.html

[+] https://aws.amazon.com/opensearch-service/pricing/#Reserved_Instance_pricing

Are OpenSearch Reserved Instances automatically applied to running on-demand OpenSearch instances?

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