EKS managed nodes billing with Reserved instance

AWS Documentation states "EC2 RIs provide a discounted hourly rate and an optional capacity reservation for EC2 instances. AWS Billing automatically applies your RI’s discounted rate when attributes of EC2 instance usage match attributes of an active RI".

Reserved Instances are applied to any matching EC2 instance usage in your account, including those used by EKS managed node group, so purchasing RIs for c4.4xlarge used as standard EC2 instances or as part of EKS managed node group will be covered by your Reserved Instance. Please see a previously accepted answer here.

Hello Om,

Reserved Instances (RIs) can be a cost-effective way to save money on AWS EC2 instances, but they do not apply to Amazon EKS managed node groups directly. RIs are specific to EC2 instances and work on a regional level. However, you can still optimize your costs when using EKS with managed node groups by understanding how EC2 RIs work and making informed decisions.

Here's how it works:

1. EC2 Reserved Instances:

   • When you purchase EC2 Reserved Instances, you are essentially committing to using specific instance types within a specific AWS region for a predetermined duration (1 or 3 years).
   • The billing benefit of RIs applies when you launch EC2 instances of the same instance type, in the same region, and within the same family (e.g., c4) as the purchased RIs.
   • EC2 RIs provide significant cost savings compared to On-Demand instances but are used explicitly for EC2 instances.

2. EKS Managed Node Groups:

   • EKS managed node groups simplify the management of EC2 instances in an EKS cluster. They automatically provision, scale, and update nodes in your cluster.
   • Managed node groups use EC2 instances, but they are managed by EKS and do not directly interact with EC2 RIs.

Now, here's how you can optimize costs when using EKS and managed node groups:

• Use Autoscaling: Configure your managed node group to use autoscaling. This way, the group can automatically scale the number of nodes based on your workload requirements, helping you avoid over-provisioning.

• Purchase RIs for Other EC2 Workloads: While RIs purchased for specific EC2 instance types won't directly apply to your EKS managed node group, you can still purchase RIs for other EC2 instances or workloads within the same AWS region to maximize cost savings.

• Monitor and Adjust: Continuously monitor your EKS cluster's resource utilization and the associated EC2 instances. If you find that you consistently need a specific instance type and size, you might consider purchasing RIs for those specific instances in addition to managing node group instances.

• Savings Plans: AWS offers Savings Plans, which provide more flexibility compared to RIs and can apply to a broader range of services, including EC2 instances. You can use Savings Plans to potentially save on EC2 costs within the same AWS region as your EKS cluster.

In summary, while EC2 Reserved Instances themselves do not directly apply to EKS managed node groups, you can optimize costs by carefully managing your EC2 instances and considering RIs or Savings Plans for other EC2 workloads in the same region. Continuously monitoring and adjusting your resources based on usage patterns will help you achieve the best cost savings.

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