GitHub Action: CDK Diff

Diff two cdk.out directories.

Usage

For all possible inputs and outputs see the Action YAML file.

Usage: Comment on Pull Request

This action is most useful for generating a diff of the generated CDK cloud assembly whenever you submit a pull request. Here is an example workflow:

name: pr

on:
  pull_request:
    branches:
      - master

# Needed because a merge commit could be generated and needs an author
env:
  GIT_AUTHOR_NAME: github-actions[bot]
  GIT_AUTHOR_EMAIL: 41898282+github-actions[bot]@users.noreply.github.com
  GIT_COMMITTER_NAME: GitHub
  GIT_COMMITTER_EMAIL: noreply@github.com

jobs:
  cdk-diff:
    runs-on: ubuntu-latest
    steps:
      - name: Setup NodeJS
        uses: actions/setup-node@v4
        with:
          node-version: "18"

      # Modify or remove based on your CDK language
      - name: Setup Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.11"

      - name: Install CDK
        run: npm install -g aws-cdk@2

      - name: Checkout main
        uses: actions/checkout@v4
        with:
          ref: main
          fetch-depth: 0

      # Modify based on how your project installs dependencies
      - name: Install main dependencies
        run: pip install pip-tools && pip-sync

      - name: CDK synth main
        run: cdk synth -o base.cdk.out

      - name: Checkout PR branch
        uses: actions/checkout@v4
        with:
          ref: ${{ github.head_ref }}
          fetch-depth: 0
          clean: false

      - name: Merge main to PR branch
        run: git merge origin/main

      # Modify based on how your project installs dependencies
      - name: Install PR branch dependencies
        run: pip-sync

      - name: CDK synth PR branch
        run: cdk synth -o head.cdk.out

      - name: Diff CDK synth outputs
        id: diff
        uses: blackboard-innersource/gh-action-cdk-diff@v1

      - name: Find Comment
        uses: peter-evans/find-comment@v3
        id: fc
        with:
          issue-number: ${{ github.event.pull_request.number }}
          comment-author: "github-actions[bot]"
          body-includes: CloudFormation

      - name: Create or update comment
        uses: peter-evans/create-or-update-comment@v4
        with:
          comment-id: ${{ steps.fc.outputs.comment-id }}
          issue-number: ${{ github.event.pull_request.number }}
          body-path: ${{ steps.diff.outputs.comment_file }}
          edit-mode: replace

Overall, what this workflow is doing:

Running cdk synth on the main branch.
Running cdk synth on the pull request branch.
Diffing the outputs of those two synths.
Posting new or updating existing comment in the pull request with the diff.

You can also only comment on the pull request when there is a diff by using if:

- name: Comment on Pull Request
  if: steps.diff.outputs.has_diff == 1
  # etc...

Developing

To run tests locally:

make

License

Please see the LICENSE file.