如何在AWS Step Functions代码中检查SNS Topic是否为空

完全可以直接在Step Functions中完成SNS Topic订阅状态的检查，不需要额外编写Lambda函数——利用Step Functions的AWS服务集成能力，直接调用SNS的ListSubscriptionsByTopic API，再通过Choice状态判断返回结果即可。

实现步骤 #

1. 配置Step Functions调用SNS API
   在状态机中添加一个Task状态，使用aws:sns:listSubscriptionsByTopic集成，传入目标SNS Topic的ARN。

2. 通过Choice状态判断订阅是否为空
   调用API后，Step Functions会返回包含订阅列表的Subscriptions数组，通过判断该数组的长度是否为0，即可确定Topic是否为空。

状态机示例代码 #

{
  "Comment": "检查SNS Topic是否为空",
  "StartAt": "ListSNSsubscriptions",
  "States": {
    "ListSNSsubscriptions": {
      "Type": "Task",
      "Resource": "arn:aws:states:::aws-sdk:sns:listSubscriptionsByTopic",
      "Parameters": {
        "TopicArn": "arn:aws:sns:us-east-1:123456789012:your-topic-name"
      },
      "Next": "CheckIfTopicIsEmpty"
    },
    "CheckIfTopicIsEmpty": {
      "Type": "Choice",
      "Choices": [
        {
          "Variable": "$.Subscriptions.length",
          "NumericEquals": 0,
          "Next": "TopicIsEmpty"
        }
      ],
      "Default": "TopicHasSubscriptions"
    },
    "TopicIsEmpty": {
      "Type": "Pass",
      "End": true,
      "Result": "该SNS Topic无任何订阅"
    },
    "TopicHasSubscriptions": {
      "Type": "Pass",
      "End": true,
      "Result": "该SNS Topic存在订阅"
    }
  }
}

权限注意事项 #

确保Step Functions的执行角色拥有sns:ListSubscriptionsByTopic权限，可在角色的IAM策略中添加如下语句：

{
  "Effect": "Allow",
  "Action": "sns:ListSubscriptionsByTopic",
  "Resource": "arn:aws:sns:us-east-1:123456789012:your-topic-name"
}

内容的提问来源于stack exchange，提问作者Johan Sánchez