When using AWS LocalStack, even if you create a CloudFormation stack from a YAML file, the template body is saved in JSON format

Platform
1

using LocalStack.

I am creating LocalStack using the following Dockercompose.

services:
  localstack:
    container_name: localstack
    image: localstack/localstack:4.0.3
    ports:
      - "127.0.0.1:4566:4566"
    environment:
      - DEBUG=1

When using LocalStack, creating a stack based on the following file and then retrieving the stack’s template body results in it being obtained in JSON format instead of YAML format. I expected it to be retrieved in YAML format. Why is this happening?

When creating a stack in a regular AWS environment using the same YAML file and then retrieving the template body, it is obtained in YAML format.

  • test/test-cloudformation.yaml
---
AWSTemplateFormatVersion: '2010-09-09'
Description: 'Resources'
Parameters:
  Env:
    Type: 'String'
    Description: 'Environment Name'
    AllowedValues:
      - 'dev'
      - 'stg'
      - 'prd'
  ResourcePrefix:
    Type: 'String'
    Description: 'Resources Prefix'
    Default: 'prefix'


Resources:
  # S3 Bucket
  S3Bucket:
    Type: 'AWS::S3::Bucket'
    DeletionPolicy: 'Retain'
    UpdateReplacePolicy: 'Retain'
    Properties:
      BucketName: !Sub '${Env}-${ResourcePrefix}-stack-test'
      VersioningConfiguration:
        Status: 'Enabled'
      PublicAccessBlockConfiguration:
        BlockPublicAcls: true
        BlockPublicPolicy: true
        IgnorePublicAcls: true
        RestrictPublicBuckets: true
  • test/parameters/test-cloudformation/test.json
[
    {
        "ParameterKey": "Env",
        "ParameterValue": "dev"
    }
]


$ aws cloudformation create-stack --region ap-northeast-1 --stack-name test-cloudfomation --endpoint-url=http://localhost:4566 --profile cfn-deploy-localstack --template-body file://test/test-cloudformation.yaml --parameters file://test/parameters/test-cloudformation/test.json

$ aws cloudformation get-template --endpoint-url=http://localhost:4566 --profile cfn-deploy-localstack --stack-name test-cloudfomation | jq -r '.TemplateBody'

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Resources",
  "Parameters": {
    "Env": {
      "Type": "String",
      "Description": "Environment Name",
      "AllowedValues": [
        "dev",
        "stg",
        "prd"
      ]
    },
    "ResourcePrefix": {
      "Type": "String",
      "Description": "Resources Prefix",
      "Default": "prefix"
    }
  },
  "Resources": {
    "S3Bucket": {
      "Type": "AWS::S3::Bucket",
      "DeletionPolicy": "Retain",
      "UpdateReplacePolicy": "Retain",
      "Properties": {
        "BucketName": {
          "Fn::Sub": "${Env}-${ResourcePrefix}-stack-test"
        },
        "VersioningConfiguration": {
          "Status": "Enabled"
        },
        "PublicAccessBlockConfiguration": {
          "BlockPublicAcls": true,
          "BlockPublicPolicy": true,
          "IgnorePublicAcls": true,
          "RestrictPublicBuckets": true
        }
      },
      "LogicalResourceId": "S3Bucket"
    }
  },
  "StackName": "test-cloudfomation",
  "StackId": "arn:aws:cloudformation:ap-northeast-1:000000000000:stack/test-cloudfomation/c8a7a9bb",
  "Outputs": {},
  "Conditions": {},
  "Mappings": {}
}

Any assistance would be greatly appreciated.

2

Hi @keny1111,

I can confirm the discrepancy in the outputs and have added an item to the engineering team’s backlog for further investigation.

1 Like
3

Hi @Marcel

Thank you for confirming!

Also, thank you for adding it to the backlog! By the way, how long will the investigation approximately take?

4

My colleague has already investigated and he was provided a yaml-structured response. Therefore, we need to conduct further investigation.

Please see our documentation on different type of support at Help & Support | Docs. We do our best to resolve the issues, but we do not provide an ETA for community reports.

Note that community support is provided on a best-effort basis and is not guaranteed. Users are encouraged to help others by sharing their knowledge and experiences.

1 Like
5

Hi @keny1111,

We successfully reproduced the issue.

As a potential workaround, you can use deploy instead of `create-stack which will provide you with a correct YAML output.

1 Like