AWS lambda 无法承担由 cloudformation 触发的角色

Question

Lambda 在通过 CloudFormation 脚本触发时无法承担跨账户角色。

我有一个 CloudFormation 脚本，它在账户 A 中创建并触发 Lambda 函数。此函数需要从账户 B 复制一个对象。我正在使用基于角色的跨账户访问。

在账户 B 上，我有以下角色，出于测试目的，我使用 S3 完全访问权限。

CrossAccountAccessRole: 
    Type: 'AWS::IAM::Role'
    Properties: 
      RoleName: 'CrossAccountAccessRole'
      Path: '/'
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: 
            AWS: !Sub 'arn:aws:iam::<AccountA>:role/CustomerCrossAccountAccessRole'
          Action: sts:AssumeRole  
  CrossAccountAccessPolicy:
    Type: "AWS::IAM::ManagedPolicy"
    Properties:
      Path: '/'
      ManagedPolicyName: CrossAccountAccessPolicy
      Roles: 
        - !Ref CrossAccountAccessRole
      PolicyDocument:
        Version: "2012-10-17"
        Statement:       
        - Effect: Allow
          Action:
            - s3:*

在账户 A 上，我有以下角色，执行 lambda，S3 完全访问和代入角色策略。

  CustomerCrossAccountAccessRole:
    Type: 'AWS::IAM::Role'
    Properties:
      RoleName: CustomerCrossAccountAccessRole
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      Path: /
      Policies:
        - PolicyName: LambdaBasicExecutionPolicy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Effect: Allow
                Action:
                  - 'logs:CreateLogGroup'
                  - 'logs:CreateLogStream'
                  - 'logs:PutLogEvents'
                Resource: '*'
        - PolicyName: LambdaSourceBucketPolicy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              Effect: Allow
              Action: 's3:*'
              Resource: '*'
        - PolicyName: LambdaAssumeRolePolicy
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
            - Effect: Allow
              Action: sts:AssumeRole
              Resource: !Sub 'arn:aws:iam::<AccountA>:role/CrossAccountAccessRole'

我运行这个 python 脚本在我的 lambda 函数中，

    try:
        print('Assume role of a cross account access role')
        boto_sts_client=boto3.client('sts', region_name='ap-southeast-2')
        stsresponse = boto_sts_client.assume_role(
            RoleSessionName = 'CrossAccountAccessSession',
            RoleArn = 'arn:aws:iam::<AccountA>:role/CrossAccountAccessRole',
                DurationSeconds = 3000
        )

        s3_assumed_client = boto3.client(
            's3',
            region_name='ap-southeast-2',
            aws_access_key_id = stsresponse["Credentials"]["AccessKeyId"],
            aws_secret_access_key = stsresponse["Credentials"]["SecretAccessKey"],
            aws_session_token = stsresponse["Credentials"]["SessionToken"]
        )
        s3_assumed_client.download_file(<BucketName>, <FilePath>,<FileName>)
    except:
        traceback.print_exc()

CloudFormation脚本returns出现如下错误，

botocore.exceptions.ClientError: An error occurred (AccessDenied) when calling the AssumeRole operation: Access denied

但是如果我在测试模式下运行相同的 Lambda（使用 CloudFormation 脚本创建）（使用 AWS 控制台上的 "Test" 按钮），它会毫无错误地下载文件。

谢谢

Answer 1

您的政策包含以下错误：

信任策略应将帐户 A 指定为委托人，这意味着来自该帐户的授权用户可以使用 CrossAccountAccessRole 角色。您不能直接在策略中指定不同账户中 users/roles 的 ARN。
account-A 中的管理员必须附加一个策略，允许角色为 CrossAccountAccessRole 的 ARN 调用 AssumeRole。
确保在创建时将 CustomerCrossAccountAccessRole 分配给 Lambda。

CrossAccountAccessRole: 
    Type: 'AWS::IAM::Role'
    Properties: 
      RoleName: 'CrossAccountAccessRole'
      Path: '/'
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: 
            AWS: 'arn:aws:iam::<AccountA>:root'
...

- PolicyName: LambdaAssumeRolePolicy
      PolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Action: sts:AssumeRole
          Resource: 'arn:aws:iam::<AccountB>:role/CrossAccountAccessRole'

stsresponse = boto_sts_client.assume_role(
   RoleSessionName = 'CrossAccountAccessSession',
   RoleArn = 'arn:aws:iam::<Account-B>:role/CrossAccountAccessRole',
   DurationSeconds = 3000
)

您在几个地方 (ARN) 写了 Account-A，实际上它应该是 Account-B，但我猜这些是错别字。

Answer 2

您不需要为此管理跨帐户角色。您可以简单地允许从目标存储桶策略中的帐户 A 进行访问。为您的 lambda 角色附加权限，您可以直接访问存储桶而无需承担任何角色。转到您的 S3 存储桶，转到权限选项卡并单击 'Bucket Policy'。您的政策看起来像，

{
    "Version": "2008-10-17",
    "Statement": [
        {
            "Sid": "DelegateReadToAccountA",
            "Effect": "Allow",
            "Principal": {
                "AWS": [
                    "arn:aws:iam::<account-A>:root"
                ]
            },
            "Action": [
                "s3:Get*",
                "s3:List*"
            ],
            "Resource": [
                "arn:aws:s3:::<bucket_name>",
                "arn:aws:s3:::<bucket_name>/*"
            ]
        }
    ]
}

AWS lambda 无法承担由 cloudformation 触发的角色

AWS lambda cannot assume a role triggered by cloudformation

amazon-web-services

amazon-cloudformation

aws-lambda

assume-role