hello.ign.json

{
    "ignition": {
        "config": {},
        "security": {
            "tls": {}
        },
        "timeouts": {},
        "version": "2.2.0"
    },
    "networkd": {},
    "passwd": {
        "users": [
            {
                "name": "core",
                "sshAuthorizedKeys": [
                    "ssh-rsa AAAAB...",
                ]
            }
        ]
    },
    "storage": {
        "files": [
            {
                "contents": {
                    "source": "data:text/plain;charset=utf-8;base64,aGVsbG8gZnJvbSBpZ25pdGlvbiEK",
                    "verification": {}
                },
                "filesystem": "root",
                "mode": 384,
                "path": "/hello"
            }
        ]
    }
}