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Add nodes/change the instance type of the AWS EKS cluster

This runbook covers how to increase the number of nodes in an eks cluster and/or change the instance type (worker_node_machine_type)

This can address the problem of CPU high usage/load

Add nodes to the eks cluster


1. Ensure you have access to the Cloud Platform AWS account

2. Access to the EKS cluster

Access to the EKS cluster

Cluster configuration:


git crypt unlock to see the following code:

 node_groups = {
    default_ng = {
      desired_capacity = var.cluster_node_count
      max_capacity     = 30
      min_capacity     = 1
      subnets          = data.aws_subnet_ids.private.ids

      instance_type = var.worker_node_machine_type
      k8s_labels = {
        Terraform = "true"
        Cluster   = local.cluster_name
        Domain    = local.cluster_base_domain_name
      additional_tags = {
        default_ng = "true"

variable "vpc_name" {
  description = "The VPC name where the cluster(s) are going to be provisioned. VPCs are created in cloud-platform-network"
  default     = ""

variable "cluster_node_count" {
  description = "The number of worker node in the cluster"
  default     = "4"

variable "worker_node_machine_type" {
  description = "The AWS EC2 instance types to use for worker nodes"
  default     = "m4.large"


There is an issue that you cannot update the default “cluster_node_count” (in isolation) with terraform - unless you increase the default “worker_node_machine_type” too.
The issue is to do with auto-scaling complexities utilising Terrafom - please see here

Therefore you either have to update default “worker_node_machine_type” to - in above example “m4.xlarge” and also the default “cluster_node_count” to - in above example “5” or “6”

Or you have to edit the “Desired size” in the “AWS EKS dashboard Edit Node Group” (once you have carried out the AWS dashboard change - update the terraform config, terraform apply accordingly - so that it is in sync with the AWS dashboard):

AWS dashboard EKS - Edit Node Group:

Group size
Minimum size
Set the minimum number of nodes that the group can scale in to.
Maximum size
Set the maximum number of nodes that the group can scale out to.
Desired size
Set the desired number of nodes that the group should launch with initially.

Change the AWS EKS instance type (worker_node_machine_type)

  • update default “worker_node_machine_type” to - in above example “m4.xlarge”

  • A ‘terraform plan’ will show that that it will replace the existing nodes

  • `terraform apply’ the changes in the usual way

  • monitor how the update is going in the AWS Autoscaling dashboard:

Note that it will create the instances/nodes before it deletes the existing - so there should be no down time

This page was last reviewed on 22 May 2023. It needs to be reviewed again on 22 August 2023 by the page owner #cloud-platform .
This page was set to be reviewed before 22 August 2023 by the page owner #cloud-platform. This might mean the content is out of date.