StackSetsで予算設定・通知機能を作ってみた！

AWSTemplateFormatVersion: '2010-09-09'
Description: Stack that creates an AWS budget, notifications, and a Lambda function that will shut down EC2 instances

Parameters:
  BudgetAmount:
    Type: Number
    Description: Maximum permissible spend for the month
  Email:
    Type: String
    Description: Email address to deliver notifications to
  WarningThreshold:
    Type: Number
    Description: Percentage of forecast monthly spend for the warning notification
    Default: 80
  WebhookUrl:
    Type: String
    Description: Webhook URL for send message to slack
  SlackUser:
    Type: String
    Description: Name for mension for slack

Outputs:
  BudgetId:
    Value: !Ref Budget

Resources:
  WarningTopic:
    Type: AWS::SNS::Topic

  WarningTopicPolicy:
    Type: AWS::SNS::TopicPolicy
    Properties:
      PolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Action: sns:Publish
            Resource: "*"
            Principal:
              Service: budgets.amazonaws.com
      Topics:
        - !Ref WarningTopic

  Budget:
    Type: AWS::Budgets::Budget
    Properties:
      Budget:
        BudgetLimit:
          Amount: !Ref BudgetAmount
          Unit: USD
        TimeUnit: MONTHLY
        BudgetType: COST
      NotificationsWithSubscribers:
        - Notification:
            NotificationType: ACTUAL
            ComparisonOperator: GREATER_THAN
            Threshold: !Ref WarningThreshold
          Subscribers:
            - SubscriptionType: EMAIL
              Address: !Ref Email
            - SubscriptionType: SNS
              Address: !Ref WarningTopic

  BudgetLambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
            Action:
              - sts:AssumeRole
      Path: /
      Policies:
        - PolicyName: BudgetLambdaExecutionRolePolicy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Effect: Allow
                Action:
                  - logs:CreateLogGroup
                  - logs:CreateLogStream
                  - logs:PutLogEvents
                Resource: arn:aws:logs:*:*:log-group:/aws/lambda/*-BudgetLambdaFunction-*:*

  BudgetLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Description: Lambda function to be called after a critical budget threshold has been exceeded
      Handler: index.lambda_handler
      Role: !GetAtt BudgetLambdaExecutionRole.Arn
      Runtime: python3.9
      Timeout: 20
      Environment:
        Variables:
          WEBHOOK_URL : !Ref WebhookUrl
          USER : !Ref SlackUser
      Code:
        ZipFile: |
          import boto3
          import os
          import json
          import urllib

          def send_slack():
              user_name = os.environ['USER']
              send_data = {
                  "text": f"<@{user_name}>\nサンドボックス環境が予算を超過しそうです。\nリソースの整理をお願いします。",
              }
              send_text = json.dumps(send_data)
              request = urllib.request.Request(
                  os.environ['WEBHOOK_URL'], 
                  data=send_text.encode('utf-8'), 
                  method="POST"
              )
              with urllib.request.urlopen(request) as response:
                  response_body = response.read().decode('utf-8')
              return 

          def lambda_handler(event, context):
              # TODO implement
              try:
                  send_slack()
              except Exception as e:
                  print(e)
                  raise e

  WarningTopicSubscription:
    Type: AWS::SNS::Subscription
    Properties:
      Protocol: lambda
      TopicArn: !Ref WarningTopic
      Endpoint: !GetAtt BudgetLambdaFunction.Arn

  BudgetLambdaFunctionPermission:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:InvokeFunction
      FunctionName: !Ref BudgetLambdaFunction
      Principal: sns.amazonaws.com
      SourceArn: !Ref WarningTopic