Change Elastic Search Instance when you have reservation purchased

Question

We have an Elastic Search Instance and we have purchased a reservation for it. Since reservation is matching with the Region and Instance Size we use, it worked well so far. But we want to change the instance size. In this case we think reservation will not match with the instance and will create double cost. So how can we also update the reservation that matches with the new instance size?

Answer

Hi Zubair,
You are correct that your existing reservation will not apply to a node of a different size.  From the documentation [1]:

> 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.

Our best practice is to modernize and right-size your OpenSearch clusters (i.e. update to newer instance generations and move to instance sizes appropriate for the workload) first, then make reserved node purchases.  Have you considered scaling your cluster out to additional nodes instead of scaling up to larger ones?  That would allow you to continue taking advantage of your existing reserved instances, and only pay on-demand for your additional capacity.

[1] https://docs.aws.amazon.com/opensearch-service/latest/developerguide/ri.html

Change Elastic Search Instance when you have reservation purchased

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