Using a Docker Action in Workflow

Learn how to integrate a reusable custom Docker container action across repositories. In this guide, we’ll invoke the docker-action-pr-giphy-comment action from the solar-system project to post a thank-you GIF on pull requests.

The image shows a GitHub repository page for "docker-action-pr-giphy-comment," displaying files and recent commits.

1. Open the Target Repository

Navigate to your solar-system repository on GitHub:

This image shows a GitHub repository page named "solar-system" with various files and folders listed, including workflows, images, and JavaScript files. The repository has no stars or forks and includes a recent pull request merge.

2. Add the Giphy API Token

Your custom action fetches GIFs using the Giphy API. To configure:

Get an API key from the Giphy Developer Portal.
In your repo, go to Settings > Actions > Secrets and variables > Actions.
Click New repository secret.
Name it GIPHY_API and paste the API key.
Save.

The image shows a GitHub repository settings page focused on "Actions secrets and variables," displaying options for managing environment and repository secrets.

The image shows a GitHub repository settings page where a new secret is being added under "Actions secrets," with the name "GIPHY_API" and a secret key entered.

Note

Never expose your API keys in plain text. Always use GitHub Secrets for sensitive values.

3. Create the Workflow File

Checkout a branch (e.g., main or a feature branch) and add .github/workflows/pr-thank-you.yml:

The image shows a GitHub interface where a user is creating or editing a file named "pr-thank" in the ".github/workflows" directory of a repository. The file content area is currently empty.

Workflow Configuration

# .github/workflows/pr-thank-you.yml
name: PR Thank You Comment

on:
  pull_request:
    types: [opened]

jobs:
  pr-action:
    runs-on: ubuntu-latest
    permissions:
      issues: write
      pull-requests: write
    steps:
      - name: Post PR Comment with Giphy
        uses: siddharth-7/docker-action-pr-giphy-comment@main
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          giphy-api-key: ${{ secrets.GIPHY_API }}

Permissions Reference

Permission	Purpose
`issues: write`	Post comments on issues
`pull-requests: write`	Manage PR comments

Commit and push your branch, then open a pull request:

4. Observe the Workflow Run

Once the PR is created, GitHub Actions will trigger the workflow automatically:

The image shows a GitHub pull request page for creating a file named "pr-thank-you.yml" with details about the branch, checks, and merge status.

Monitor progress under the Actions tab:

The image shows a GitHub Actions page with a workflow named "pr-thank-you.yml" in progress. The sidebar lists options like Caches, Deployments, and Runners.

After success, the action posts a thank-you GIF comment on the pull request.

5. Behind the Scenes: Docker Build Logs

Each run of a container action rebuilds the Docker image. Example build output:

#1 [internal] load .dockerignore
#1 DONE 0.0s
#2 [internal] load build definition from Dockerfile
#2 DONE 0.0s
#3 [internal] load metadata for docker.io/library/alpine:3.10
#3 DONE 0.0s
#6 [1/4] FROM docker.io/library/alpine:3.10
#6 DONE 0.1s
#9 [4/4] RUN chmod +x /entrypoint.sh
#9 DONE 0.3s

And the execution command:

/usr/bin/docker run --name 2c046f464a14829b2e7791b519b_32bdb \
  --label 461ce --workdir /github/workspace -m -1 \
  --input_github_token="INPUT_GITHUB_TOKEN" \
  -e "GIPHY_API" -e "GITHUB_SHA"="GITHUB_SHA" \
  -v "/var/run/docker.sock":"/var/run/docker.sock" \
  --rm docker-action-pr-giphy-comment:main

Performance Tip

Rebuilding the Docker image each run adds latency. For faster CI workflows, consider authoring a JavaScript action that executes without a container build.

References

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