CloudFormation中的数学运算

是否有可能在Cloudformation json模板中执行某种数学运算？

我遇到了两个有用的区域:1.设置IOPS,它需要是磁盘大小的比率.2.为RDS免费存储空间设置Cloud Watch警报.将其设置为磁盘大小的百分比将是有用的.

在内部函数不支持的CloudFormation模板中执行自定义逻辑有两种通用解决方案,例如数学运算:

1.自定义资源

编写自定义资源以执行数学运算,将输入作为属性传递,并将输出作为值传递.这是一个独立的工作示例,它Result: 13作为堆栈输出返回:

Resources:
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: {Service: [lambda.amazonaws.com]}
          Action: ['sts:AssumeRole']
      Path: "/"
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
  AddFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        ZipFile: !Sub |
          var response = require('cfn-response');
          exports.handler = function(event, context) {
            var result = parseInt(event.ResourceProperties.Op1) + parseInt(event.ResourceProperties.Op2);
            response.send(event, context, response.SUCCESS, {Value: result});
          };
      Runtime: nodejs
  AddTest:
    Type: Custom::Add
    Properties:
      ServiceToken: !GetAtt AddFunction.Arn
      Op1: 8
      Op2: 5
Outputs:
  Result:
    Description: Result
    Value: !GetAtt AddTest.Value

2.模板预处理器

使用您选择的全功能模板语言/平台编写"源"模板,生成有效的CloudFormation模板作为输出.您可以使用功能齐全的CloudFormation特定库,如对流层,但编写简单的预处理器层以满足您的用例和编程语言/库首选项也很容易.

我目前的选择是嵌入式Ruby(ERB),主要是因为我已经熟悉它了.这是一个template.yml.erb使用嵌入式Ruby语法执行数学运算的示例文件,该操作Result: 13作为堆栈输出返回:

Resources:
  # CloudFormation stacks require at least one resource
  Dummy:
    Type: AWS::SNS::Topic
Outputs:
  Result:
    Description: Result
    Value: <%= 8 + 5 %>

要运行模板,请运行cat template.yml.erb | ruby -rerb -e "puts ERB.new(ARGF.read, nil, '-').result" > template.yml,该模板会将以下CloudFormation-ready模板写入template.yml:

Resources:
  # CloudFormation stacks require at least one resource
  Dummy:
    Type: AWS::SNS::Topic
Outputs:
  Result:
    Description: Result
    Value: 13