本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 使用 Lambda 函數回應事件
<a name="event-lambda-response"></a>

此程序示範如何使用 在 Amazon EventBridge 上 AWS Lambda 接聽、使用 Amazon Simple Notification Service (SNS) 建立通知，以及將調查結果發佈至 AWS Security Hub CSPM，為管理員和安全團隊提供可見性。<a name="lambda-setup"></a>

**設定 Lambda 函數和 IAM 角色**

1. 首先設定 AWS Identity and Access Management (IAM) 角色，並定義 Lambda 函數所需的許可。此安全性最佳實務可讓您彈性地指定誰擁有呼叫函數的授權，以及限制授與該使用者的許可。不建議直接在使用者帳戶下執行大多數 AWS 操作，尤其是在管理員帳戶下。

   前往 [https://console.aws.amazon.com/iam/](https://console.aws.amazon.com/iam/) 開啟 IAM 主控台。

1. 使用 JSON 政策編輯器來建立以下範本中定義的政策。提供您自己的區域和 AWS 帳戶詳細資訊。如需詳細資訊，請參閱[在 JSON 索引標籤上建立政策](https://docs.aws.amazon.com/IAM/latest/UserGuide/access_policies_create-console.html#access_policies_create-json-editor)。

------
#### [ JSON ]

****  

   ```
   {
       "Version":"2012-10-17",		 	 	 
       "Statement": [
           {
               "Sid": "LambdaCertificateExpiryPolicy1",
               "Effect": "Allow",
               "Action": "logs:CreateLogGroup",
               "Resource": "arn:aws:logs:us-east-1:123456789012:*"
           },
           {
               "Sid": "LambdaCertificateExpiryPolicy2",
               "Effect": "Allow",
               "Action": [
                   "logs:CreateLogStream",
                   "logs:PutLogEvents"
               ],
               "Resource": [
                   "arn:aws:logs:us-east-1:123456789012:log-group:/aws/lambda/handle-expiring-certificates:*"
               ]
           },
           {
               "Sid": "LambdaCertificateExpiryPolicy3",
               "Effect": "Allow",
               "Action": [
                   "acm:DescribeCertificate",
                   "acm:GetCertificate",
                   "acm:ListCertificates",
                   "acm:ListTagsForCertificate"
               ],
               "Resource": "*"
           },
           {
               "Sid": "LambdaCertificateExpiryPolicy4",
               "Effect": "Allow",
               "Action": "SNS:Publish",
               "Resource": "*"
           },
           {
               "Sid": "LambdaCertificateExpiryPolicy5",
               "Effect": "Allow",
               "Action": [
                   "SecurityHub:BatchImportFindings",
                   "SecurityHub:BatchUpdateFindings",
                   "SecurityHub:DescribeHub"
               ],
               "Resource": "*"
           },
           {
               "Sid": "LambdaCertificateExpiryPolicy6",
               "Effect": "Allow",
               "Action": "cloudwatch:ListMetrics",
               "Resource": "*"
           }
       ]
   }
   ```

------

1. 建立 IAM 角色，並將新政策連接到該角色。如需有關建立 IAM 角色和連接政策的資訊，請參閱[為 AWS 服務建立角色 （主控台）](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-service.html#roles-creatingrole-service-console)。

1. 在 https：//[https://console.aws.amazon.com/lambda/](https://console.aws.amazon.com/lambda/) 開啟 AWS Lambda 主控台。

1. 建立 Lambda 函數。如需詳細資訊，請參閱[使用主控台建立 Lambda 函數](https://docs.aws.amazon.com/lambda/latest/dg/getting-started-create-function.html)。請完成下列步驟：

   1. 在 **Create function (建立函數)** 頁面上，選擇 **Author from scratch (從頭開始撰寫)** 選項來建立函數。

   1. 在 **Function name (函數名稱)** 欄位中指定名稱，例如「handle-expiring-certificates」。

   1. 在 **Runtime (執行時間)** 清單中選擇 Python 3.8。

   1. 展開 **Change default execution role (變更預設執行角色)**，然後選擇 **se an existing role (使用現有角色)**。

   1. 從 **Existing role (現有角色)** 清單中選擇您稍早建立的角色。

   1. 選擇**建立函數**。

   1. 在 **Function code (函數程式碼)** 底下插入以下程式碼：

      ```
      # Copyright 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
      # SPDX-License-Identifier: MIT-0
      #
      # Permission is hereby granted, free of charge, to any person obtaining a copy of this
      # software and associated documentation files (the "Software"), to deal in the Software
      # without restriction, including without limitation the rights to use, copy, modify,
      # merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
      # permit persons to whom the Software is furnished to do so.
      #
      # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
      # INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
      # PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
      # HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
      # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
      # SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
      
      import json
      import boto3
      import os
      from datetime import datetime, timedelta, timezone
      # -------------------------------------------
      # setup global data
      # -------------------------------------------
      utc = timezone.utc
      # make today timezone aware
      today = datetime.now().replace(tzinfo=utc)
      # set up time window for alert - default to 45 if its missing
      if os.environ.get('EXPIRY_DAYS') is None:
          expiry_days = 45
      else:
          expiry_days = int(os.environ['EXPIRY_DAYS'])
      expiry_window = today + timedelta(days = expiry_days)
      def lambda_handler(event, context):
          # if this is coming from the ACM event, its for a single certificate
          if (event['detail-type'] == "ACM Certificate Approaching Expiration"):
              response = handle_single_cert(event, context.invoked_function_arn)
          return {
              'statusCode': 200,
              'body': response 
          }
      def handle_single_cert(event, context_arn):
          cert_client = boto3.client('acm')
          cert_details = cert_client.describe_certificate(CertificateArn=event['resources'][0])
          result = 'The following certificate is expiring within ' + str(expiry_days) + ' days: ' + cert_details['Certificate']['DomainName']
          # check the expiry window before logging to Security Hub and sending an SNS
          if cert_details['Certificate']['NotAfter'] < expiry_window:
              # This call is the text going into the SNS notification
              result = result + ' (' + cert_details['Certificate']['CertificateArn'] + ') '
              # this call is publishing to SH
              result = result + ' - ' + log_finding_to_sh(event, cert_details, context_arn)
              # if there's an SNS topic, publish a notification to it
              if os.environ.get('SNS_TOPIC_ARN') is None:
                  response = result
              else:
                  sns_client = boto3.client('sns')
                  response = sns_client.publish(TopicArn=os.environ['SNS_TOPIC_ARN'], Message=result, Subject='Certificate Expiration Notification')
          return result
      def log_finding_to_sh(event, cert_details, context_arn):
          # setup for security hub
          sh_region = get_sh_region(event['region'])
          sh_hub_arn = "arn:aws:securityhub:{0}:{1}:hub/default".format(sh_region, event['account'])
          sh_product_arn = "arn:aws:securityhub:{0}:{1}:product/{1}/default".format(sh_region, event['account'])
          # check if security hub is enabled, and if the hub arn exists
          sh_client = boto3.client('securityhub', region_name = sh_region)
          try:
              sh_enabled = sh_client.describe_hub(HubArn = sh_hub_arn)
          # the previous command throws an error indicating the hub doesn't exist or lambda doesn't have rights to it so we'll stop attempting to use it
          except Exception as error:
              sh_enabled = None
              print ('Default Security Hub product doesn\'t exist')
              response = 'Security Hub disabled'
          # This is used to generate the URL to the cert in the Security Hub Findings to link directly to it
          cert_id = right(cert_details['Certificate']['CertificateArn'], 36)
          if sh_enabled:
              # set up a new findings list
              new_findings = []
                  # add expiring certificate to the new findings list
              new_findings.append({
                  "SchemaVersion": "2018-10-08",
                  "Id": cert_id,
                  "ProductArn": sh_product_arn,
                  "GeneratorId": context_arn,
                  "AwsAccountId": event['account'],
                  "Types": [
                      "Software and Configuration Checks/AWS Config Analysis"
                  ],
                  "CreatedAt": event['time'],
                  "UpdatedAt": event['time'],
                  "Severity": {
                      "Original": '89.0',
                      "Label": 'HIGH'
                  },
                  "Title": 'Certificate expiration',
                  "Description": 'cert expiry',
                  'Remediation': {
                      'Recommendation': {
                          'Text': 'A new certificate for ' + cert_details['Certificate']['DomainName'] + ' should be imported to replace the existing imported certificate before expiration',
                          'Url': "https://console.aws.amazon.com/acm/home?region=" + event['region'] + "#/?id=" + cert_id
                      }
                  },
                  'Resources': [
                      {
                          'Id': event['id'],
                          'Type': 'ACM Certificate',
                          'Partition': 'aws',
                          'Region': event['region']
                      }
                  ],
                  'Compliance': {'Status': 'WARNING'}
              })
              # push any new findings to security hub
              if new_findings:
                  try:
                      response = sh_client.batch_import_findings(Findings=new_findings)
                      if response['FailedCount'] > 0:
                          print("Failed to import {} findings".format(response['FailedCount']))
                  except Exception as error:
                      print("Error: ", error)
                      raise
          return json.dumps(response)
      # function to setup the sh region    
      def get_sh_region(event_region):
          # security hub findings may need to go to a different region so set that here
          if os.environ.get('SECURITY_HUB_REGION') is None:
              sh_region_local = event_region
          else:
              sh_region_local = os.environ['SECURITY_HUB_REGION']
          return sh_region_local
      # quick function to trim off right side of a string
      def right(value, count):
          # To get right part of string, use negative first index in slice.
          return value[-count:]
      ```

   1. 在 **Environment variables (環境變數)** 底下，選擇 **Edit (編輯)** 並選擇性新增以下變數。
      + (選用) EXPIRY\$1DAYS

        指定傳送憑證過期通知的前置時間 (以天為單位)。此函數預設值為 45 天，但您可以指定自訂值。
      + (選用) SNS\$1TOPIC\$1ARN

        指定 Amazon SNS 的 ARN。用下列格式提供完整的 ARN：arn:aws:sns:*<region>*:*<account-number>*:*<topic-name>*。
      + (選用) SECURITY\$1HUB\$1REGION

        指定不同 AWS Security Hub CSPM 區域中的 。如果沒有指定，便會使用執行中 Lambda 函數使用的區域。如果函數在多個區域中執行，建議您將所有憑證訊息移至單一區域中的 Security Hub CSPM。

   1. 在 **Basic settings (基本設定)** 下，將 **Timeout (逾時)** 設為 30 秒。

   1. 請在頁面頂端選擇 **Deploy (部署)**。

完成下列程序中的任務，以開始使用此解決方案。

**自動執行電子郵件過期通知程序**

在本範例中，我們在透過 Amazon EventBridge 引發事件時，會為每個即將過期的憑證提供一封單一電子郵件。根據預設，ACM 每天會針對過期前 45 天或以下天數的憑證引發事件。（此期間可使用 ACM API 的 [PutAccountConfiguration](https://docs.aws.amazon.com/acm/latest/APIReference/API_PutAccountConfiguration.html) 操作進行自訂。) 這些事件都會觸發下列串聯的自動化動作：

```
ACM raises Amazon EventBridge event → 
>>>>>>> events

          Event matches Amazon EventBridge rule → 

                    Rule calls Lambda function → 

                              Function sends SNS email and logs a Finding in Security Hub CSPM
```

1. 建立 Lambda 函數並設定許可。(已完成 - 請參閱「[設定 Lambda 函數和 IAM 角色](#lambda-setup)」)。

1. 為 Lambda 函數建立*標準* SNS 主題，用來傳出通知。如需詳細資訊，請參閱[建立 Amazon SNS 主題](https://docs.aws.amazon.com/sns/latest/dg/sns-create-topic.html)。

1. 任何對訂閱新 SNS 主題感興趣的人。如需詳細資訊，請參閱[訂閱 Amazon SNS 主題](https://docs.aws.amazon.com/sns/latest/dg/sns-create-subscribe-endpoint-to-topic.html)。

1. 建立 Amazon EventBridge 規則來觸發 Lambda 函數。如需詳細資訊，請參閱[建立回應事件的 Amazon EventBridge 規則](https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-create-rule.html)。

   前往 [https://console.aws.amazon.com/events/](https://console.aws.amazon.com/events/) 進入 Amazon EventBridge 主控台中，導覽至 **Events** (事件) > **Rules** (規則) 頁面，然後選擇 **Create rule** (建立規則)。指定 **Service Name (服務名稱)**、**Event Type (事件類型)**以及 **Lambda function (Lambda 函數)**。在 **Event Pattern preview (事件模式預覽)** 編輯器中，貼上以下程式碼：

   ```
   {
     "source": [
       "aws.acm"
     ],
     "detail-type": [
       "ACM Certificate Approaching Expiration"
     ]
   }
   ```

   事件 (例如 Lambda 接收的事件) 會顯示在 **Show sample event(s) (顯示範例事件)** 底下：

   ```
   {
     "version": "0",
     "id": "9c95e8e4-96a4-ef3f-b739-b6aa5b193afb",
     "detail-type": "ACM Certificate Approaching Expiration",
     "source": "aws.acm",
     "account": "123456789012",
     "time": "2020-09-30T06:51:08Z",
     "region": "us-east-1",
     "resources": [
       "arn:aws:acm:us-east-1:123456789012:certificate/61f50cd4-45b9-4259-b049-d0a53682fa4b"
     ],
     "detail": {
       "DaysToExpiry": 31,
       "CommonName": "My Awesome Service"
     }
   }
   ```

**清理方式**

一旦您不再需要範例組態或任何組態，最佳實務是移除該組態的所有軌跡，避免安全問題和未來的非預期費用：
+ IAM 政策及角色
+ Lambda 函式
+ CloudWatch Events 規則
+ 與 Lambda 相關聯的 CloudWatch Logs
+ SNS 主題