Serverless AWS Pseudo Parameters

Currently, it's impossible (or at least, very hard) to use the CloudFormation Pseudo Parameters in your serverless.yml.

This plugin fixes that.

You can now use #{AWS::AccountId}, #{AWS::Region}, etc. in any of your config strings, and this plugin replaces those values with the proper pseudo parameter Fn::Sub CloudFormation function.

You can also use any other CloudFormation resource id as a reference, eg #{myAwesomeResource}, will replace it with a reference to that resource. #{myAwesomeResource.property} works as well.

Installation

Install the package with npm: npm install serverless-pseudo-parameters, and add it to your serverless.yml plugins list:

plugins:
  - serverless-pseudo-parameters

Usage

Add one of the pseudo parameters to any resource parameter, and it will be replaced during deployment. Mind you to replace the default ${} with a #{}. So ${AWS::AccountId}, becomes: #{AWS::AccountId} etc.

• using #{MyResource} to be rewritten to ${MyResource}, which is roughly equivalent to {"Ref": "MyResource"}
• using #{MyResource.Arn} to be rewritten to ${MyResource.Arn}, which is roughly equivalent to {"Fn::GetAtt": ["MyResource", "Arn"]}.

For example, this configuration will create a bucket with your account id appended to the bucket name:

service: users-bucket-thingy

plugins:
  - serverless-pseudo-parameters

functions:
  users:
    handler: users.handler
    events:
      - s3:
          bucket: photos-#{AWS::AccountId}
          event: s3:ObjectRemoved:*

The output in the cloudformation template will look something like this:

"Type": "AWS::S3::Bucket",
"Properties": {
  "BucketName": {
    "Fn::Sub": "photos-${AWS::AccountId}"
  },
}

Or use it to generate Arn's, for example for Step Functions:

service: foobar-handler

plugins:
  - serverless-pseudo-parameters

functions:
  foobar-baz:
    handler: foo.handler

stepFunctions:
  stateMachines:
    foobar:
      definition:
        Comment: "Foo!"
        StartAt: bar
        States:
          bar:
            Type: Task
            Resource: "arn:aws:lambda:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-foobar-baz"
            End: true

Properties

The plugin used to automatically replace hardcoded regions in serverless.yml in previous releases. This not done anymore by default. This behaviour can enabled again by using:

custom:
  pseudoParameters:
    skipRegionReplace: false

Disable referencing other resources

You can also disable the referencing of internal resources:

custom:
  pseudoParameters:
    allowReferences: false