Add support for Graviton instances

[danrg]

Graviton instances are based on ARM 64 bit architecture and offer great price/performance ratios.
I tried adding a new node group (ng2) for Graviton instances:

  node_groups = {
    ng1 = {
      disk_size        = 20
      desired_capacity = 2
      max_capacity     = 4
      min_capacity     = 1
      instance_types   = ["t3.small"]
      capacity_type    = "SPOT"
      additional_tags  = var.tags
      k8s_labels       = {}
    }

    ng2 = {
      disk_size        = 20
      desired_capacity = 1
      max_capacity     = 4
      min_capacity     = 1
      instance_types   = ["t4g.small"]
      capacity_type    = "SPOT"
      additional_tags  = var.tags
      k8s_labels       = {}
    }

  }

Applying the Terraform code results in an error. The error message shows it tries to use x86 Amazon Linux 2 image, which is not valid, since it needs the ARM64 bit image:

│ Error: error creating EKS Node Group (staging:staging-ng2-enhanced-grubworm): InvalidParameterException: [t4g.small] is not a valid instance type for requested amiType AL2_x86_64
│ {
│ RespMetadata: {
│ StatusCode: 400,
│ RequestID: "73318df5-e6c3-4e1e-ad3b-7b209bc182f6"
│ },
│ ClusterName: "staging",
│ Message_: "[t4g.small] is not a valid instance type for requested amiType AL2_x86_64",
│ NodegroupName: "staging-ng2-enhanced-grubworm"
│ }
│
│ with module.eks.module.eks.module.node_groups.aws_eks_node_group.workers["ng2"],
│ on .terraform/modules/eks.eks/modules/node_groups/node_groups.tf line 1, in resource "aws_eks_node_group" "workers":
│ 1: resource "aws_eks_node_group" "workers" {
│

Thank you!

[seethatgo]

Adding some other info from @danrg
Example Graviton TF impl: https://github.com/niallthomson/eks-graviton-terraform

the critical bits are: ami_type = "AL2_ARM_64" so that it uses the ARM64 image, and instance_types from the separate nodegroup should be Graviton2 ones (such as m6g.medium)

Graviton1 is not supported (a1 instances), and Graviton3 is too new

[sekka1]

@seethatgo @danrg is the blocker here not being able to set the base AMI for the EKS nodes?

[danrg]

@sekka1 Indeed, setting another AMI is the blocker here, as Graviton nodes need an ARM AMI.