Use CloudFormation Pseudo Parameters in your Serverless project
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Latest commit c652ffa Aug 21, 2018

README.md

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