Calculator of DynamoDB reserved capacity via CloudFormation

01-lambda-exec-role.yaml

# Should be deployed first as it exports "LambdaRoleExecutionARN" which is used by other stacks.
Resources:
  LambdaRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          -
            Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
            Action: "sts:AssumeRole"
      Policies:
        -
          PolicyName: LambdaLogToCloudWatch
          PolicyDocument:
            Version: "2012-10-17"
            Statement:
              -
                Effect: Allow
                Action:
                  - "logs:CreateLogGroup"
                  - "logs:CreateLogStream"
                  - "logs:PutLogEvents"
                Resource: "arn:aws:logs:*:*:*"
Outputs:
  LambdaRoleExecution:
    Value: !GetAtt LambdaRole.Arn
    Description: Common role used by Lambda with the minimum actions
    Export:
      Name: LambdaRoleExecutionARN

02-demo-reserved-capacity-calc.yaml

# DependsOn 0007-common-lambda-exec-role.yaml
# Caculation of dynamodB reserved capacity leveraging Custom resources (lambda)
Parameters:
  ItemsCountPerSecondRead:
    Type: Number
    Description: Nbe of items to read per second
  IsStronglyRead:
    Type: String
    AllowedValues: [true, false]
    Default: true
    Description: Strongly Read ?
  ItemSizeRead:
    Type: Number
    Description: Item Size in Read (Kb)
  ItemsCountPerSecondWrite:
    Type: Number
    Description: Nbe of items to write per second
  ItemSizeWrite:
    Type: Number
    Description: Item Size in Write (Kb)

Resources:
  GetReservedCapacityFunction:
    Type: AWS::Lambda::Function
    Properties:
      Role: !ImportValue LambdaRoleExecutionARN
      Handler: "index.handler"
      Runtime: "nodejs6.10"
      Timeout: 120
      Code:
        ZipFile: |
          const response = require('cfn-response');

          function getReadCapacity({itemsCount, itemsRequiredTimeRead, itemSize}, isStrongRead) {
            const READ_UNIT  = 4 ;//kb
            const itemsPerSecond = itemsCount/itemsRequiredTimeRead;
            const itemReadUnits =  Math.ceil(itemSize / READ_UNIT)
            const readThroughput =  itemReadUnits * itemsPerSecond;
            return  Math.ceil(isStrongRead ? readThroughput : (readThroughput/2));
          }

          function getWriteCapacity({itemsCount, itemsRequiredTimeWrite, itemSize}) {
            const WRITE_UNIT= 1; //kb
            const itemsPerSecond = itemsCount/ itemsRequiredTimeWrite;
            const itemWriteUnits = Math.ceil(itemSize/ WRITE_UNIT);
            return Math.ceil(itemWriteUnits * itemsPerSecond);
          }

          exports.handler = function(event, context) {
            if (event.RequestType === 'Delete') {
              return response.send(event, context, response.SUCCESS);
            }
            if (event.RequestType === 'Create' || event.RequestType  === 'Update') {
              const readCapacity = getReadCapacity({
                itemsCount: parseFloat(event.ResourceProperties.itemsCountPerSecondRead),
                itemsRequiredTimeRead: 1,
                itemSize: parseFloat(event.ResourceProperties.itemSizeRead)
              }, event.ResourceProperties.isStronglyRead === 'true');
              const writeCapacity= getWriteCapacity({
                itemsCount: parseFloat(event.ResourceProperties.itemsCountPerSecondWrite),
                itemsRequiredTimeWrite: 1,
                itemSize: parseFloat(event.ResourceProperties.itemSizeWrite)
              });
              
              return response.send(event, context, response.SUCCESS, {
                readCapacity,
                writeCapacity
              });
            }
          }

  GetReservedCapacity:
    Type: Custom::GetReservedCapacity
    Properties:
      ServiceToken: !GetAtt GetReservedCapacityFunction.Arn
      itemsCountPerSecondRead: !Ref ItemsCountPerSecondRead
      itemSizeRead: !Ref ItemSizeRead
      isStronglyRead: !Ref IsStronglyRead
      itemsCountPerSecondWrite: !Ref ItemsCountPerSecondWrite
      itemSizeWrite: !Ref ItemSizeWrite
Outputs:
  ReadCapacity:
    Value: !GetAtt GetReservedCapacity.readCapacity
  WriteCapacity:
    Value: !GetAtt GetReservedCapacity.writeCapacity