针对 EC2 上面的应用程序，不要分配 User Credentials，使用 IAM Role Attachment。
可以访问 EC2 的 meatdata 查看赋予的 Role 权限

curl http://169.254.169.254/latest/meta-data/iam/security-credentials/

二、Software on local laptop

针对在自己电脑上面开发测试的用户，用户需要 S3 的访问权限，不给用户分配权限，这样可以避免 AK/SK 丢失造成的损失，我们可以给 User 分配一个 Cross accunt role，让用户使用接口 assume-role 获取临时的 AK/SK，然后去访问AWS 资源。

2.1、创建用户 alice

不给用户分配任何权限。

最后得到用户的 AK/SK

Access key ID ：AKIA5NAGHF6N2WFTQZP6
Secret access key：TqJ/9Hg450x204r1lai+C3w0+3kvVOeTckPZhvau

2.2、创建一个跨账户 Role

给角色增加权限。

生成的 Role ARN：arn:aws:iam::921283538843:role/alice-sts

给 alice 赋予 assume role 的权限。

Policy 格式如下：

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "sts:AssumeRole",
            "Resource": "arn:aws:iam::921283538843:role/alice-sts"
        }
    ]
}

2.3、测试用户权限

直接使用 AK/SK，查看用户是否有相应的权限。
使用 aws configure 配置。

wangzan:~/.aws $ aws configure
AWS Access Key ID [****************H6YU]: AKIA5NAGHF6N2WFTQZP6
AWS Secret Access Key [****************bVA/]: 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
Default region name [us-east-1]: 
Default output format [json]: 
wangzan:~/.aws $ aws sts get-caller-identity
{
    "Account": "921283538843", 
    "UserId": "AIDA5NAGHF6NZASTSA7Y6", 
    "Arn": "arn:aws:iam::921283538843:user/alice"
}
wangzan:~/.aws $ aws s3 ls
An error occurred (AccessDenied) when calling the ListBuckets operation: Access Denied

直接使用是获取不到权限的，那我们使用 assume-role。

wangzan:~/.aws $ aws sts assume-role --role-arn arn:aws:iam::921283538843:role/alice-sts --role-session-name s3-access --external-id alice
{
    "AssumedRoleUser": {
        "AssumedRoleId": "AROA5NAGHF6NSZZVCDMHE:s3-access", 
        "Arn": "arn:aws:sts::921283538843:assumed-role/alice-sts/s3-access"
    }, 
    "Credentials": {
        "SecretAccessKey": "sJuL4gzx6ScdloJyyO6J4mCnFdtMcFm/uAPVjOz7", 
        "SessionToken": "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", 
        "Expiration": "2019-12-27T11:04:52Z", 
        "AccessKeyId": "ASIA5NAGHF6NZJHS6VVN"
    }
}

然后去编辑 ~/.aws/credentials，把生成的Credentials放到里面，如下：

[default]
aws_access_key_id = ASIA5NAGHF6NZJHS6VVN
aws_secret_access_key = sJuL4gzx6ScdloJyyO6J4mCnFdtMcFm/uAPVjOz7
aws_session_token = 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

然后再去请求 S3。

wangzan:~/.aws $ aws sts get-caller-identity
{
    "Account": "921283538843", 
    "UserId": "AROA5NAGHF6NSZZVCDMHE:s3-access", 
    "Arn": "arn:aws:sts::921283538843:assumed-role/alice-sts/s3-access"
}

2.4、自动更换临时权限

修改 ~/.aws/credentials，出现了一点问题，我就把那个Role 里面的限制取消了，也就是那个 external-id。

[alice]
aws_access_key_id = AKIA5NAGHF6N2WFTQZP6
aws_secret_access_key = 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
aws_session_token =

[default]
role_arn = arn:aws:iam::921283538843:role/alice-sts
source_profile = alice

可以看下目前的 Role。

wangzan:~/.aws $ aws sts get-caller-identity
{
    "Account": "921283538843", 
    "UserId": "AROA5NAGHF6NSZZVCDMHE:botocore-session-1577441862", 
    "Arn": "arn:aws:sts::921283538843:assumed-role/alice-sts/botocore-session-1577441862"
}