RDS CloudWatch告警需要IAM角色来授权CloudFormation访问相关资源。您可以在CloudFormation模板中使用以下代码来创建IAM角色：

"MyIAMRole": {
    "Type": "AWS::IAM::Role",
    "Properties": {
        "AssumeRolePolicyDocument": {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Effect": "Allow",
                    "Principal": {
                        "Service": [
                            "cloudformation.amazonaws.com"
                        ]
                    },
                    "Action": [
                        "sts:AssumeRole"
                    ]
                }
            ]
        },
        "Policies": [
            {
                "PolicyName": "MyPolicy",
                "PolicyDocument": {
                    "Version": "2012-10-17",
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Action": [
                                "rds:DescribeDBInstances",
                                "cloudwatch:GetMetricStatistics",
                                "sns:Publish"
                            ],
                            "Resource": "*"
                        }
                    ]
                }
            }
        ]
    }
}

您可以将上面的IAM角色添加到您的CloudFormation模板中，同时将其分配给RDS CloudWatch Alarm。示例代码如下：

"Alarms": {
    "Type": "AWS::CloudWatch::Alarm",
    "Properties": {
        "AlarmName": "MyAlarm",
        "AlarmDescription": "My RDS alarm",
        "MetricName": "CPUUtilization",
        "Namespace": "AWS/RDS",
        "Statistic": "Average",
        "Period": "60",
        "EvaluationPeriods": "5",
        "Threshold": "80",
        "ComparisonOperator": "GreaterThanOrEqualToThreshold",
        "Dimensions": [
            {
                "Name": "DBInstanceIdentifier",
                "Value": {"Ref": "MyDBInstance"}
            }
        ],
        "AlarmActions": [
            {"Ref": "MySNSTopic"}
        ],
        "OKActions": [
            {"Ref": "MySNSTopic"}
        ],
        "InsufficientDataActions": []
    },
    "DependsOn": ["MyIAMRole"]
}

在上