本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。

# 使用 Lambda 函数响应事件
<a name="event-lambda-response"></a>

此过程演示 AWS Lambda 如何使用在亚马逊上监听 EventBridge、使用亚马逊简单通知服务 (SNS) Simple Notification Service 创建通知以及如何向其发布调查结果 AWS Security Hub CSPM，从而为管理员和安全团队提供可见性。<a name="lambda-setup"></a>

**设置 Lambda 函数和 IAM 角色**

1. 首先配置 AWS Identity and Access Management (IAM) 角色并定义 Lambda 函数所需的权限。通过此安全性最佳实践，您可以灵活地指定谁有权调用该函数，并限制授予该用户的权限。不建议直接在用户帐户下运行大多数 AWS 操作，尤其不要在管理员帐户下运行。

   使用 [https://console.aws.amazon.com/iam/](https://console.aws.amazon.com/iam/) 打开 IAM 控制台。

1. 使用 JSON 策略编辑器创建在以下模板中定义的策略。提供您自己的地区和 AWS 账户详情。有关更多信息，请参阅[在“JSON”选项卡上创建策略](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. 创建 IAM 角色并向其附加新策略。有关创建 IAM 角色和附加策略的信息，请参阅[为 AWS 服务创建角色（控制台）](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-service.html#roles-creatingrole-service-console)。

1. 打开 AWS Lambda 控制台，网址为[https://console.aws.amazon.com/lambda/](https://console.aws.amazon.com/lambda/)。

1. 创建 Lambda 函数。有关更多信息，请参阅[使用控制台创建 Lambda 函数](https://docs.aws.amazon.com/lambda/latest/dg/getting-started-create-function.html)。完成以下步骤：

   1. 在**创建函数**页面上，选择 **Author from scratch（从头开始创作）**选项以创建函数。

   1. 在**函数名称字段中指定一个名称**，例如 handle-expiring-certificates “”。

   1. 在 **Runtime（运行时）**列表中，选择“Python 3.8”。

   1. 展开 **Change default execution role（更改默认执行角色）**，然后选择 **Use an existing role（使用现有角色）**。

   1. 从 **Existing role（现有角色）**列表中选择您先前创建的角色。

   1. 选择**创建函数**。

   1. 在 **Function code（函数代码）**下，插入以下代码。

      ```
      # 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（环境变量）**下，选择 **Edit（编辑）**并可选择添加以下变量。
      + （可选）EXPIRY\$1DAYS

        指定发送证书过期通知之前的准备时间（天数）。此函数默认为 45 天，但您可以指定自定义值。
      + （可选）SNS\$1TOPIC\$1ARN

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

        在不同的区域 AWS Security Hub CSPM 中指定。如果未指定此选项，则使用正在运行的 Lambda 函数的区域。如果该函数在多个区域运行，则可能需要将所有证书消息发送到单个区域中的 Security Hub CSPM。

   1. 在 **Basic settings（基本设置）**下，将 **Timeout（超时）**设置为 30 秒。

   1. 在页面顶部，选择 **Deploy（部署）**。

完成以下过程中的任务以开始使用此解决方案。

**自动发送过期电子邮件通知**

在此示例中，当通过 Amazon EventBridge 发起活动时，我们为每份即将到期的证书提供一封电子邮件。预设情况下，ACM 每天都会为距离过期日 45 天或更短时间的证书引发一个事件。（此时间段可以使用 ACM API 的 [PutAccountConfiguration](https://docs.aws.amazon.com/acm/latest/APIReference/API_PutAccountConfiguration.html) 操作自定义。） 这些事件中的每一个都会触发以下级联的自动操作：

```
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. 创建 Lambda 函数并配置权限。（已完成 – 请参阅 [设置 Lambda 函数和 IAM 角色](#lambda-setup)）。

1. 为 Lambda 函数创建用于发送通知的*标准* SNS 主题。有关更多信息，请参阅[创建 Amazon SNS 主题](https://docs.aws.amazon.com/sns/latest/dg/sns-create-topic.html)。

1. 为任何感兴趣的人订阅新 SNS 主题。有关更多信息，请参阅[订阅 Amazon SNS 主题](https://docs.aws.amazon.com/sns/latest/dg/sns-create-subscribe-endpoint-to-topic.html)。

1. 创建用于触发 Lambda 函数的亚马逊 EventBridge 规则。有关更多信息，请参阅[创建对事件做出反应的 Amazon EventBridge 规则](https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-create-rule.html)。

   在 Amazon EventBridge 控制台中 [https://console.aws.amazon.com/events/](https://console.aws.amazon.com/events/)，导航至**事件** > **规则**页面，然后选择**创建规则**。指定**服务名称**、**事件类型**和 **Lambda 函数**。在**事件模式预览**编辑器中，粘贴以下代码：

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

   **显示示例事件**下会显示如 Lambda 接收这样的事件：

   ```
   {
     "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**

一旦您不再需要示例配置或任何配置，最佳实践是删除该配置的所有痕迹，以避免安全问题和以后的意外费用：
+ IAM 策略和角色
+ Lambda 函数
+ CloudWatch 活动规则
+ CloudWatch 与 Lambda 关联的日志
+ SNS 主题