Describe AWS CloudFormation change set Action for GitHub Actions

Describe cfn stack diff using describe-change-set API.
cf. https://docs.aws.amazon.com/cli/latest/reference/cloudformation/describe-change-set.html

This action exports json output as an Github Action output variable that actions running later in a job can use.
Additionally, exports table formatted diff file. Below shows how to use it to post pull request comment.

ex. describe change set diff like management console.

Changed Properties is not shown on management console, but exists in describe-change-set API response.

Table of Contents

• Usage
• Environment variables
• Credentials and Region
• Permissions
• License Summary
• Contributing

Usage

  - name: checkout
    uses: actions/checkout@v2
  
  - name: configure AWS credentials
    uses: aws-actions/configure-aws-credentials@v1
    with:
      aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
      aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
      aws-region: ap-northeast-1

  - name: describe change set
    id: describe-change-set
    uses: Blue-Pix/describe-cfn-change-set@v2.1
    with:
      stack_name: omochi
      template_body: after.cf.yml

  - name: archive diff
    uses: actions/upload-artifact@v1
    with:
      name: diff
      path: ${{ steps.describe-change-set.outputs.diff_file_path }}

  - name: Download diff markdown
    uses: actions/download-artifact@v1
    with:
      name: diff

  - name: Post comments
    env:
      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
      URL: ${{ github.event.pull_request.comments_url }}
      FILE_PATH: ${{ steps.describe-change-set.outputs.diff_file_path }}
    run: |
      cat ${FILE_PATH} | xargs echo
      curl -X POST \
           -H "Authorization: token ${GITHUB_TOKEN}" \
           -d "{\"body\": \"$(cat ${FILE_PATH} | xargs echo)\"}" \
           ${URL}

for example, you set trigger on pull_request, this action posts a comment which describes change set like management console.

See action.yml for the full documentation for this action's inputs and outputs.

Environment variables

• stack_name: CloudFormation stack name to apply change. (required)
• template_body: CloudFormation template file path. (required)

Credentials and Region

Use the aws-actions/configure-aws-credentials action to configure the GitHub Actions environment with environment variables containing AWS credentials and your desired region.

Permissions

This action requires the following minimum set of permissions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "cloudformation:CreateChangeSet",
                "cloudformation:DescribeChangeSet",
                "cloudformation:DeleteChangeSet"
            ],
            "Resource": "*"
        }
    ]
}

The Action calls create-change-set api with random uuid as change set name first, then describe-change-set.
After writing output to file, remove temporary change set by delete-change-set.
Note. do not restrict change-set-name in Resource condition because change-set-name is random.
ex. ac7c731cd-b210-4e1a-a355-804847ee9156

License Summary

This code is made available under the MIT license.

Contributing

Any contributing is welcome 🎉