Serverless-cf-vars NPM

Serverless CF Vars

Installation

yarn add --dev serverless-cf-vars

npm i --save-dev serverless-cf-vars

Add it to your serverless.yml plugins list:

plugins:
  - serverless-cf-vars

Usage

Whenever you want the cloudformation template to have a string that contains ${}, simply use #{} instead, and it will get transformed into correct ${} (with Fn::Sub inserted for you) in the cloudformation template before deployment.

If you want to make use of Fn::Sub with mapping you need to insert the Fn::Sub yourself and the plugin will just convert #{} into ${}.

Works on both Resources and Outputs.

Example

resources:
  Resources:
    myApiIdentityPool:
      Type: "AWS::Cognito::IdentityPool"
      Properties:
        IdentityPoolName:
          Fn::Sub:
            - "my#{thing}IdentityPool${self:custom.stage}"
            - thing: Api
        AllowUnauthenticatedIdentities: True
    cognitoUnauthRole:
      Type: 'AWS::IAM::Role'
      Properties:
        RoleName: Cognito_#{myApiIdentityPool.Name}_Unauth_Role
        AssumeRolePolicyDocument:
          Statement:
            - Effect: Allow
              Principal:
                Federated: cognito-identity.amazonaws.com
              Action: [ 'sts:AssumeRole' ]
        Policies:
          - PolicyName: cognitounauth
            PolicyDocument:
              Statement:
                - Effect: Allow
                  Action:
                    - mobileanalytics:PutEvents
                    - cognito-sync:*
                  Resource:
                    - "*"
          - PolicyName: CustomPermissions
            PolicyDocument:
              Statement:
                - Effect: Allow
                  Action:
                    - lambda:Invoke
                  Resource:
                    - "arn:aws:lambda:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${self:custom.stage}-myFunction"

Becomes

resources:
  Resources:
    myApiIdentityPool:
      Type: "AWS::Cognito::IdentityPool"
      Properties:
        IdentityPoolName: myApiIdentityPoolmyStage
        AllowUnauthenticatedIdentities: True
    cognitoUnauthRole:
      Type: 'AWS::IAM::Role'
      Properties:
        RoleName:
          Fn::Sub: Cognito_${myApiIdentityPool.Name}_Unauth_Role
        AssumeRolePolicyDocument:
          Statement:
            - Effect: Allow
              Principal:
                Federated: cognito-identity.amazonaws.com
              Action: [ 'sts:AssumeRole' ]
        Policies:
          - PolicyName: cognitounauth
            PolicyDocument:
              Statement:
                - Effect: Allow
                  Action:
                    - mobileanalytics:PutEvents
                    - cognito-sync:*
                  Resource:
                    - "*"
          - PolicyName: CustomPermissions
            PolicyDocument:
              Statement:
                - Effect: Allow
                  Action:
                    - lambda:Invoke
                  Resource:
                    - Fn::Sub:
                        "arn:aws:lambda:${AWS::Region}:${AWS::AccountId}:function:myService-myStage-myFunction"

Information

Inspired by serverless-pseudo-parameters, this plugin allows you to use Cloudformation pseudo parameters, as well as substitute in other variables.

Because the same syntax is used for variables in both serverless.yml and in cloudformation templates, there's currently no way to use variables in the generated cloudformation template. This plugin works around that by transforming #{} into ${} after serverless has taken care of all its variable substitutions.