code in https://github.com/hashicorp/packer/issues/8271

gistfile1.txt

{
    "description": "Create nomis version of cis hardened amazon linux.",
    "min_packer_version": "1.4.4",
    "variables": {
        "ansible_dir"             : "/home/ec2-user/ansible/",
        "ansible_source_location" : "s3://xxx-shared-services-devops-share/ansible-modules/",
        "aws_subnet"              : null,
        "aws_vpc"                 : null,
        "base_ami_name"           : null,
        "build_ver"               : null,
        "encryption_key"          : "aa6624eb-d789-4380-8911",
        "instance_profile"        : "gen3_generic",
        "region"                  : null,
        "ssh_username"            : "ec2-user"
    },
    "builders": [
        {
            "ami_description": "Amazon Linux2 x86_64 HVM EBS (encrypted) and CIS hardened.",
            "ami_name": "{{user `base_ami_name`}}-{{user `build_ver`}}-{{timestamp}}",
            "ami_regions": [
                "us-west-2",
                "ap-southeast-2"
            ],
            "ami_virtualization_type": "hvm",
            "associate_public_ip_address": true,
            "communicator": "ssh",
            "iam_instance_profile": "{{user `instance_profile`}}",

            "launch_block_device_mappings": [{
                "device_name": "/dev/xvda",
                "delete_on_termination": true,
                "encrypted": true,
                "kms_key_id": "aa6624eb-d789-4380-8911", 
                "volume_size": 50,
                "volume_type": "gp2"
            }],
            "region": "{{user `region`}}",
            "region_kms_key_ids": {
                "us-west-2": "aa6624eb-d789-4380-8911",
                "ap-southeast-2": "1a2d6900-52cc-4eb7"
            },
            "snapshot_users": ["99999999999"],
            "source_ami_filter": {
                "filters": {
                  "virtualization-type": "hvm",
                  "architecture": "x86_64",
                  "name": "*amzn2-ami-hvm-*",
                  "block-device-mapping.volume-type": "gp2",
                  "root-device-type": "ebs"
                },
                "owners": [
                  "amazon"
                ],
                "most_recent": true
            },
            "ssh_pty": true,
            "ssh_timeout": "10m",
            "ssh_username": "{{user `ssh_username`}}",
            "subnet_id": "{{user `aws_subnet`}}",
            "tags": {
                "Name": "{{user `base_ami_name`}}-{{user `build_ver`}}",
                "OS": "AMAZONLINUX",
                "OSVER": "2"
            },
            "type": "amazon-ebs",
            "vpc_id": "{{user `aws_vpc`}}"
        }
    ]
}