Question

通过CloudFormation脚本触发时，Lambda无法承担跨帐户角色。

我有一个CloudFormation脚本，该脚本可以在帐户A中创建并触发Lambda函数。该函数需要从帐户B复制对象。我正在使用基于角色的跨帐户访问权限。

在帐户B上，我担任以下角色：出于测试目的，我正在使用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:*

在帐户A上，我担任以下角色，包括lambda执行，S3完全访问权限和假定的角色策略。

  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'

我在lambda函数中运行此python脚本，

    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脚本返回以下错误，

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“测试”按钮），它将下载文件而不会出现任何错误。

谢谢

Answer 1

您的政策包含以下错误：

信任策略应将帐户A指定为主体，这意味着该帐户的授权用户可以使用CrossAccountAccessRole角色。您不能直接在策略中为不同帐户中的用户/角色指定ARN。
帐户A中的管理员必须附加一个策略，该策略允许角色为CrossAccountAccessRole的ARN调用AssumeRole。
确保在创建Lambda时已将CustomerCrossAccountAccessRole分配给了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
)

您在几个实际应该是帐户B的地方（ARN）中写了帐户A，但我想这些是错别字。

Answer 2

您无需为此管理跨帐户角色。您只需在目标存储桶的策略内允许帐户A进行访问即可。附加您的lambda角色的权限，您就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”标签，然后单击“存储桶策略”。您的政策如下，

{
    "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

2 个答案: