[budget alerts]Serverless Framework と AWS Budgets で日次の利用料金が想定より高かったらSlackへ通知する(Cost Anomaly Detectionは採用見送り)

$ grep VERSION= /etc/os-release 
VERSION="20.04.3 LTS (Focal Fossa)"
$ sls --version
Framework Core: 3.2.0
Plugin: 6.0.0
SDK: 4.3.1
$ npm --version
6.14.16
$ nodejs --version
v10.19.0

# .env
# .envはserverless.ymlと同じディレクトリに配置

# AWS
REGION="***"

# slack incoming webhook
SLACK_WEBHOOK_URL="https://hooks.slack.com/services/***"

service: src
frameworkVersion: '3'
useDotenv: true

provider:
  name: aws
  region: ${env:REGION}
  runtime: nodejs14.x
  memorySize: 128
  timeout: 300

# Lambdaの実行環境でnpmパッケージを使うことが出来るようにpackage.jsonなどを転送
# 転送しているファイル
# $ ls lambdaLayer/nodejs/
# node_modules  package.json  package-lock.json
#
#
# https://docs.aws.amazon.com/lambda/latest/dg/configuration-layers.html
#
layers:
  layerName:
    path: lambdaLayer
    description: npm package layers

plugins:
  - serverless-dotenv-plugin

functions:
  slack-notify:
    # Lambdaのエントリーポイント
    handler: src/slack-notify.handler
    name: slack-notify
    events:
      - sns:
          arn: !Ref snsTopic
          topicName: snsTopic
    environment:
      TZ: Asia/Tokyo
      SLACK_WEBHOOK_URL: ${env:SLACK_WEBHOOK_URL}
    layers:
      # Refでlayersでデプロイしているnpmパッケージを参照するようにし、Lambdaの実行環境にpackage.jsonとpackage-lock.jsonを配置する
      - { Ref: LayerNameLambdaLayer }

resources:
略

    snsTopic:
略
    snsTopicPolicy:
略


  Outputs:
略

service: src
frameworkVersion: '3'
useDotenv: true

provider:
略

layers:
略

plugins:
略

functions:
略

resources:
  Description: "Set billing/budget alerts for the AWS account."
  Resources:
    # GUIでは https://docs.aws.amazon.com/cost-management/latest/userguide/budgets-create.html#create-cost-budget
    dailyBudget:
      Type: "AWS::Budgets::Budget"
      Properties:
        # https://docs.aws.amazon.com/ja_jp/AWSCloudFormation/latest/UserGuide/aws-properties-budgets-budget-budgetdata.html
        Budget:
          BudgetName: Daily
          BudgetType: COST
          # 今回は日次で予算管理したいので。他に月次、四半期、年次も指定可能。
          # 月次はMONTHLY、　四半期はQUARTERLY、年次ANNUALLY
          TimeUnit: DAILY
          BudgetLimit:
            # "TimeUnit"で指定したスパンで管理したい予算金額。
            # なお、ここでのアラートの閾値は"Amount"のN%といった具合に決めていく
            Amount: 20
            Unit: USD
        # https://docs.aws.amazon.com/ja_jp/AWSCloudFormation/latest/UserGuide/aws-properties-budgets-budget-notification.html
        NotificationsWithSubscribers:
        　# https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-budgets-budget-notification.html
          - Notification:
              NotificationType: ACTUAL # FORECASTEDも指定可能
              ComparisonOperator: GREATER_THAN
              Threshold: 50 # "Amount"の50%に到達したら通知
              ThresholdType: PERCENTAGE
            Subscribers:
            - SubscriptionType: SNS
              Address: { Ref: snsTopic }
          - Notification:
              NotificationType: ACTUAL
              ComparisonOperator: GREATER_THAN # 他にEQUAL_TOとLESS_THANも指定可能
              Threshold: 90 # "Amount"の90%に到達したら通知
              ThresholdType: PERCENTAGE # 他にABSOLUTE_VALUE、絶対値も指定可能
            Subscribers:
            - SubscriptionType: SNS
              Address: { Ref: snsTopic }

    # "NotificationsWithSubscribers"で作成したアラートをAmazon SNSで受け取る
    snsTopic:
      Type: AWS::SNS::Topic
      Properties:
        DisplayName: aws-budget-alert-to-slack-topic
        TopicName: aws-budget-alert-to-slack-topic

    # "snsTopic"を定義するだけでは以下のエラーを引いてしまう。"snsTopicPolicy"も必要！
    # How to fix ERORR "Your budget must have permissions to send a notification to your topic " on AWS
    # https://stackoverflow.com/questions/70021257/how-to-fix-erorr-your-budget-must-have-permissions-to-send-a-notification-to-yo
    snsTopicPolicy:
      Type: AWS::SNS::TopicPolicy
      Properties:
        PolicyDocument:
          {
            "Version": "2008-10-17",
            "Id": "__default_policy_ID",
            "Statement": [
              {
                "Sid": "AWSBudgetsSNSPublishingPermissions",
                "Effect": "Allow",
                "Principal": {
                  "Service": "budgets.amazonaws.com"
                },
                "Action": "SNS:Publish",
                # Fn::Subは変数と文字列を結合するために使っている。ここではRegionとAccountId
                # https://dev.classmethod.jp/articles/cloud%E2%80%8Bformation-intrinsic-function-memorandum/
                # RegionとAccountIdはAWS CloudFormation によって事前定義されたパラメータ、Pseudo parameters(疑似パラメータ)であり、AWS::Regionなどと使う
                # https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/pseudo-parameter-reference.html
                "Resource": !Sub "arn:aws:sns:${AWS::Region}:${AWS::AccountId}:aws-budget-alerts-to-slack-topic"
            },
            {
              "Sid": "__default_statement_ID",
              "Effect": "Allow",
              "Principal": {
                "AWS": "*"
              },
              "Action": [
                  "SNS:GetTopicAttributes",
                  "SNS:SetTopicAttributes",
                  "SNS:AddPermission",
                  "SNS:RemovePermission",
                  "SNS:DeleteTopic",
                  "SNS:Subscribe",
                  "SNS:ListSubscriptionsByTopic",
                  "SNS:Publish",
                  "SNS:Receive"
              ],
              "Resource": !Sub "arn:aws:sns:${AWS::Region}:${AWS::AccountId}:aws-budget-alerts-to-slack-topic",
              "Condition": {
                "StringEquals": {
                  "AWS:SourceOwner": !Ref "AWS::AccountId"
                }
              }
            }
          ]
        }
        Topics:
          - { Ref: snsTopic }

  # sls deployが完了してから出力したいもの
  Outputs:
    DailyBudgetId:
      Value: 
        Ref: dailyBudget
    snsTopicArn:
      Description: "ARN of SNS Topic"
      Value:
        Ref: snsTopic

const request = require('request-promise-native');

const sendMessage = (message) => {
    return request({
        method: 'POST',
        url: process.env.SLACK_WEBHOOK_URL,
        body: message,
        json: true,
    })
        .then((body) => {
            if (body === 'ok') {
                return {};
            } else {
                throw new Error(body);
            }
        });
};

const processRecord = (record) => {
    console.log(`record: ${JSON.stringify(record)}`);
    return sendMessage({
        // @here AWS Budgets: Daily has exceeded your alert threshold
        text: '<!here> ' + record.Sns.Subject,
        attachments: [{
            fields: [{
                title: 'Type',
                value: record.Sns.Type,
                short: true,
            }, {
                title: 'Time',
                value: record.Sns.Timestamp,
                short: true,
            }, {
                title: 'MessageId',
                value: record.Sns.MessageId,
                short: false,
            }, {
                title: 'Message',
                value: record.Sns.Message,
                short: false,
            }],
        }],
    });
};

/*
example event:
{
    "EventSource": "aws:sns",
    "EventVersion": "1.0",
    "EventSubscriptionArn": "arn:aws:sns:<REGION>:<xxxxxxxxx>:src-dev-snsTopic-<xxxxxxxxx>:<xxxxxxxxx>",
    "Sns": {
        "Type": "Notification",
        "MessageId": "<xxxxxxxxx>",
        "TopicArn": "arn:aws:sns:<REGION>:<xxxxxxxxx>:src-dev-snsTopic-<xxxxxxxxx>",
        "Subject": "<SUBJECT>",
        "Message": "<MESSAGE>",
        "Timestamp": "2022-02-17T17:33:07.585Z",
        "SignatureVersion": "1",
        "Signature": "<xxxxxxxxx>",
        "SigningCertUrl": "<xxxxxxxxx>",
        "UnsubscribeUrl": "<xxxxxxxxx>",
        "MessageAttributes": {}
    }
}
*/
module.exports.handler = (event, context, callback) => {
    console.log(`event received: ${JSON.stringify(event)}`);
    Promise.all(event.Records.map(processRecord))
        .then(() => callback(null))
        .catch((err) => callback(err));
};