Packer: Packer AWS构建因AuthFailure而失败

我试图使用下面的JSON构建AMI-

{
  "variables": {
    "aws_access_key": "",
    "aws_secret_key": ""
  },
  "builders": [{
    "type": "amazon-ebs",
    "access_key": "{{user `aws_access_key`}}",
    "secret_key": "{{user `aws_secret_key`}}",
    "region": "us-east-1",
    "source_ami": "ami-9eaa1cf6",
    "instance_type": "t2.micro",
    "ssh_username": "ubuntu",
    "ami_name": "packer-example {{timestamp}}"
  }],
  "provisioners": [{
    "type": "shell",
    "inline": [
      "sleep 30",
      "sudo apt-get update",
      "sudo apt-get install -y redis-server"
    ]
  }]
}

执行以下命令进行构建-

打包程序构建-var'aws_access_key = xxxx'-var'aws_secret_key = xxxx'/EBS/packer-templates/EC2.json

但总是会出错-

==> amazon-ebs：查询AMI时出错：AuthFailure：AWS无法验证提供的访问凭证
==> amazon-ebs：状态码：401，请求ID：[]
生成“ amazon-ebs”错误：查询AMI时出错：AuthFailure：AWS无法验证提供的访问凭证
状态码：401，请求ID：[]

谁能帮我为什么会出现这些错误？ 我提供了有效的访问密钥和秘密密钥。