如何在AWS SAM模板中创建带自动扩缩容吞吐量的DynamoDB表

现有配置的前置缺失项 #

• 未明确声明DynamoDB表的计费模式为PROVISIONED，若不指定该参数，模板默认创建为按需计费模式，无法挂载预置吞吐的自动扩缩容能力
• 未为表本身、关联的全局二级索引定义基础预置吞吐值，这是自动扩缩容服务的挂载基础
• 未注册应用自动扩缩容的关联资源，完成DynamoDB表和自动扩缩容服务的权限、资源关联，否则配置不会实际生效
• 原配置存在部署级硬伤：全局二级索引用到的es、ts字段未在AttributeDefinitions中声明，会直接导致栈创建失败

完整可部署的模板配置 #

Resources:
  # DynamoDB表基础定义，补充缺失的必要配置
  myDB:
    Type: AWS::DynamoDB::Table
    Properties:
      TableName: my-awesome-database
      # 明确指定为预置吞吐量计费模式
      BillingMode: PROVISIONED
      # 表级基础预置吞吐值，作为自动扩缩容的初始基准
      ProvisionedThroughput:
        ReadCapacityUnits: 5
        WriteCapacityUnits: 5
      AttributeDefinitions:
        - AttributeName: e_id
          AttributeType: S
        # 补全全局二级索引依赖的属性定义
        - AttributeName: es
          AttributeType: S
        - AttributeName: ts
          AttributeType: N
      KeySchema:
        - AttributeName: e_id
          KeyType: HASH
      GlobalSecondaryIndexes:
        - IndexName: my-awesome-database-index
          KeySchema:
            - AttributeName: es
              KeyType: HASH
            - AttributeName: ts
              KeyType: RANGE
          Projection:
            ProjectionType: ALL
          # GSI独立预置吞吐值，作为GSI自动扩缩容的初始基准
          ProvisionedThroughput:
            ReadCapacityUnits: 5
            WriteCapacityUnits: 5

  # 自动扩缩容服务关联的IAM角色，授予最小操作权限
  DynamoDBAutoScalingRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: application-autoscaling.amazonaws.com
            Action: sts:AssumeRole
      Policies:
        - PolicyName: DynamoDBAutoScalingAccess
          PolicyDocument:
            Version: "2012-10-17"
            Statement:
              - Effect: Allow
                Action:
                  - dynamodb:DescribeTable
                  - dynamodb:UpdateTable
                  - cloudwatch:PutMetricAlarm
                  - cloudwatch:DescribeAlarms
                  - cloudwatch:GetMetricStatistics
                  - cloudwatch:SetAlarmState
                Resource: "*"

  # 表级写入容量的自动扩缩容目标注册
  TableWriteScalableTarget:
    Type: AWS::ApplicationAutoScaling::ScalableTarget
    Properties:
      RoleArn: !GetAtt DynamoDBAutoScalingRole.Arn
      ServiceNamespace: dynamodb
      ResourceId: !Sub "table/${myDB.TableName}"
      ScalableDimension: dynamodb:table:WriteCapacityUnits
      # 定义扩缩容的容量上下限
      MinCapacity: 5
      MaxCapacity: 100

  # 表级写入容量的自动扩缩容策略：基于利用率的目标跟踪模式
  TableWriteScalingPolicy:
    Type: AWS::ApplicationAutoScaling::ScalingPolicy
    Properties:
      ScalingTargetId: !Ref TableWriteScalableTarget
      PolicyName: DynamoDBTableWriteAutoScalingPolicy
      PolicyType: TargetTrackingScaling
      TargetTrackingScalingPolicyConfiguration:
        # 触发伸缩的利用率阈值，与控制台默认逻辑一致
        TargetValue: 40.0
        # 缩容冷却时间，避免频繁波动
        ScaleInCooldown: 300
        # 扩容冷却时间
        ScaleOutCooldown: 60
        DisableScaleIn: false

  # 全局二级索引写入容量的自动扩缩容目标注册
  GSIWriteScalableTarget:
    Type: AWS::ApplicationAutoScaling::ScalableTarget
    Properties:
      RoleArn: !GetAtt DynamoDBAutoScalingRole.Arn
      ServiceNamespace: dynamodb
      ResourceId: !Sub "table/${myDB.TableName}/index/${myDB.GlobalSecondaryIndexes[0].IndexName}"
      ScalableDimension: dynamodb:index:WriteCapacityUnits
      MinCapacity: 5
      MaxCapacity: 100

  # 全局二级索引写入容量的自动扩缩容策略
  GSIWriteScalingPolicy:
    Type: AWS::ApplicationAutoScaling::ScalingPolicy
    Properties:
      ScalingTargetId: !Ref GSIWriteScalableTarget
      PolicyName: DynamoDBGSIWriteAutoScalingPolicy
      PolicyType: TargetTrackingScaling
      TargetTrackingScalingPolicyConfiguration:
        TargetValue: 40.0
        ScaleInCooldown: 300
        ScaleOutCooldown: 60
        DisableScaleIn: false

关键配置注意事项 #

• 若需要为读取能力开启自动扩缩容，仅需将对应ScalableTarget的ScalableDimension替换为dynamodb:table:ReadCapacityUnits、dynamodb:index:ReadCapacityUnits，其余参数逻辑保持不变即可
• MaxCapacity参数需根据自身月度账单上限设置，避免突发流量下自动扩缩容到过高容量产生非预期成本
• 后续若计划将表切换为按需计费模式，需先删除所有上述自动扩缩容关联资源，否则会因资源模式冲突导致部署失败

内容的提问来源于stack exchange，提问作者Crazy Cat