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IPv4 Prefix Delegation

The configuration snippet below shows how to enable prefix delegation to increase the number of available IP addresses on the provisioned EC2 nodes.

VPC CNI Configuration

In this example, the vpc-cni addon is configured using before_compute = true. This is done to ensure the vpc-cni is created and updated before any EC2 instances are created so that the desired settings have applied before they will be referenced. With this configuration, you will now see that nodes created will have --max-pods 110 configured do to the use of prefix delegation being enabled on the vpc-cni.

If you find that your nodes are not being created with the correct number of max pods (i.e. - for m5.large, if you are seeing a max pods of 29 instead of 110), most likely the vpc-cni was not configured before the EC2 instances.

module "eks" {
  source  = "terraform-aws-modules/eks/aws"

  # Truncated for brevity

  cluster_addons = {
    vpc-cni = {
      before_compute = true
      most_recent    = true # To ensure access to the latest settings provided
      configuration_values = jsonencode({
        env = {
          WARM_PREFIX_TARGET       = "1"


When enabled, inspect one of the aws-node-* (AWS VPC CNI) pods to ensure prefix delegation is enabled and warm prefix target is 1:

kubectl describe ds -n kube-system aws-node | grep ENABLE_PREFIX_DELEGATION: -A 3

Output should look similar to below (truncated for brevity):

    ENABLE_PREFIX_DELEGATION:               true # <- this should be set to true
    WARM_ENI_TARGET:                        1
    WARM_PREFIX_TARGET:                     1 # <- this should be set to 1