Add provisioner to cleanup any available attached ENIs during subnet …

…destroy (#336)

This is a workaround for the known VPC CNI addon's "leaked ENIs" issue:
See aws/amazon-vpc-cni-k8s#608

Co-authored-by: Rafael Mendes Pereira <[email protected]>

modules/terraform/aws/virtual-network/main.tf

@@ -65,6 +65,32 @@ resource "aws_subnet" "subnets" {
 
   # Ensure all secondary CIDR blocks are created before subnets in secondary CIDR blocks are created
   depends_on = [aws_vpc_ipv4_cidr_block_association.secondary_ipv4_cidr_block]
+
+  provisioner "local-exec" {
+    /*
+      This command cleans up any not in use ENIs attached to this subnet, which were created outside the scope of the Terraform modules.
+      This is a workaround for the known VPC CNI addon's "leaked ENIs" issue: See https://github.com/aws/amazon-vpc-cni-k8s/issues/608
+    */
+    when    = destroy
+    command = <<-EOT
+      echo "Detaching Subnet: ${self.id} Network Interfaces"
+      # Get available (not in use) ENIs attached to this subnet
+      network_interfaces_attachment_ids=$(aws ec2 describe-network-interfaces --filters Name=subnet-id,Values=${self.id} --query "NetworkInterfaces[?Status=='available' && Attachment.AttachIndex != '0'].Attachment.AttachmentId" --output text)
+      for network_interface_attachment_id in $network_interfaces_attachment_ids; do
+        echo "Detaching available Network Interface attachment id: $network_interface_attachment_id"
+        if ! aws ec2 detach-network-interface --attachment-id $network_interface_attachment_id; then
+          echo "##[warning] Failed to detach Network Interface attachment id: $network_interface_attachment_id"
+        fi
+      done
+      network_interfaces=$(aws ec2 describe-network-interfaces --filters Name=subnet-id,Values=${self.id} --query "NetworkInterfaces[?Status=='available' && Attachment.AttachIndex != '0'].NetworkInterfaceId" --output text)
+      for network_interface in $network_interfaces; do
+        echo "Deleting available Network Interface: $network_interface"
+        if ! aws ec2 delete-network-interface --network-interface-id $network_interface; then
+          echo "##[warning] Failed to delete Network Interface: $network_interface"
+        fi
+      done
+    EOT
+  }
 }
 
 resource "aws_eip" "eips" {