CloudFormation创建EKS IAM角色报Missing required field Principal如何修复

报错是因为IAM信任策略（AssumeRolePolicyDocument）的语法层级错误，Principal、Action字段被错误写在Statement数组的同级位置，导致Statement下的唯一规则条目缺少必填的Principal字段，IAM校验不通过。

Resources:
  EKSIAMRole:
    Type: 'AWS::IAM::Role'
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - eks.amazonaws.com
            Action:
              - 'sts:AssumeRole'
      RoleName: !Ref EKSIAMRoleName
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/AmazonEKSClusterPolicy
        - arn:aws:iam::aws:policy/AmazonEKSServicePolicy

• 调整Principal、Action字段的缩进层级，使其与同一条规则的Effect字段平级，归属到同一个Statement条目下
• 所有IAM信任策略的Statement条目必须同时包含Effect、Principal、Action三个必填字段，缺一不可

内容的提问来源于stack exchange，提问作者Luong To