Referencing external config files using ${file()} fails and breaks Cloudformation template

This is a Bug Report

Description

What Went Wrong

PR #2842 indicates that it is possible to configure a service by referencing external resource files in serverless.yml as such

service: service-name

provider:
  name: aws
  runtime: python2.7

resources:
  - ${file(./dynamodb.yml)}

However, the above configuration yields an error and results in the JSON object located at .serverless/cloudformation-template-update-stack.json being populated with the individual characters of the literal string ${file(./dynamodb.yml)}

Here’s the error message that is returned:

Serverless: Packaging service...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading function .zip files to S3...
Serverless: Updating Stack...

  Serverless Error ---------------------------------------

     Invalid template property or properties [22, 10, 11,
     12, 13, 14, 15, 16, 17, 18, 19, 0, 1, 2, 3, 4, 5, 6,
     7, 8, 9, 20, 21]

  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Forums:        forum.serverless.com
     Chat:          gitter.im/serverless/serverless

  Your Environment Information -----------------------------
     OS:                 darwin
     Node Version:       4.1.1
     Serverless Version: 1.11.0

and here’s what the .serverless/cloudformation-template-update-stack.json file looks like as a result

{
  "0": "$",
  "1": "{",
  "2": "f",
  "3": "i",
  "4": "l",
  "5": "e",
  "6": "(",
  "7": ".",
  "8": "/",
  "9": "d",
  "10": "y",
  "11": "n",
  "12": "a",
  "13": "m",
  "14": "o",
  "15": "d",
  "16": "b",
  "17": ".",
  "18": "y",
  "19": "m",
  "20": "l",
  "21": ")",
  "22": "}",
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "The AWS CloudFormation template for this Serverless application",
  "Resources": {
    "ServerlessDeploymentBucket": {
      "Type": "AWS::S3::Bucket"
    }
  },
  "Outputs": {
    "ServerlessDeploymentBucketName": {
      "Value": {
        "Ref": "ServerlessDeploymentBucket"
      }
    }
  }
}

What did you expect should have happened?

The reference ${file(./dynamodb.yml)} should have caused the Serverless Framework to load the YAML config in dynamodb.yml and use that to configure resources.

What was the config you used?

see description

What stacktrace or error message from your provider did you see?

see description

Similar or dependent issues:

• #2828

Additional Data

• Serverless Framework Version you’re using: 1.11.0
• Operating System: Mac OS X El Capitan 10.11.6

[dougmoscrop]

@ubaniabalogun sorry about that, my initial implementation was naive. I’ve fixed this and added validation/tests against regression.

[dougmoscrop]

@mt-sergio you are right but this is actually a different bug. the original bug applied to the resources section, this bug has come up and causes all file-based variables to fail as far as I can tell - not just that they’re loaded poorly as ‘keys’, but that the references remain unaffected

This was introduced via commit 7cadf284440447ea8774d8abb640323713485f22