GitHub Action Using Go

This is a starting point for a GitHub Action based in Go. This repo provides all the structure needed to build a robust GitHub action using Go and following action development best practices.

Getting Started

This is a GitHub template repo, so when you click "Use this template", it will create a new copy of this template in your org or personal repo of choice. Once you have created a repo from this template, you should be able to clone and navigate to the root of the repository.

First Build

From the root of your repo, you should be able to run the following to build and test the Go action.

go build ./...
go test ./...

What's in Here?

.
├── Dockerfile
├── LICENSE
├── README.md
├── action.yaml
├── go.mod
├── go.sum
├── main.go
└── pkg
    └── tweeter
        ├── tweeter.go
        └── tweeter_test.go

action.yaml

The action.yml file contains the metadata which describes our action. This includes, but is not limited to the following.

• name, description and author
• inputs
• outputs
• branding
• runs

You will see an example structure already exists. The example executes the Dockerfile and provides to it the arguments described in the runs section. We map the sample input to the arguments of the Dockerfile.

By setting runs.using: docker we are telling the Actions runtime to execute the Dockerfile when the Action is used in a workflow.

By setting runs.image: Dockerfile we are telling the Actions runtime to build and then execute the Dockerfile at the entrypoint defined in the Dockerfile. The build for the Dockerfile will happen each time the Action is executed, which can take a considerable amount of time depending on how long it takes to build your Go code. Later, we'll change this to a pre-built image for optimization.

Dockerfile

This Dockerfile should look relatively familiar to folks who use containers to build Go code. We create a builder intermediate image based on Go 1.15.2, pull in the source, and build the application. After the application has been built, the statically linked binary is copied into a thin image, which results in an image of roughly 8 MB.

go.mod / go.sum

Go module definition which will need to be updated with the name of your module.

main.go

This is the Go entrypoint for your GitHub Action. It is a simple command line application which can be executed outside the context of the Action by running the following. This is where you will add your Go code for your Action.

.github/workflows/tweeter-automation.yaml

This is the continuous integration / CLI release automation. The release workflow defined in this automation will is triggered by tags shaped like v1.2.3, and will create a GitHub release for a pushed tag. The release will use the ./github/release.yml to automatically generate structured release notes based on pull request tags.

.github/workflows/action-version.yaml

This action triggers when a new release is published. Upon publication of the new release, this will tag the repository with the shortened major semantic version pointing at the highest semantic version within that major version. For example, v1.2.2 and v1 point to the same ref xyz, a new tag is introduced v1.2.3 which points to ref abc, this action will move the v1 tag to point to abc rather than xyz. This enables consumers of an action to take a "floating" major semantic version dependency, like my-action@v1.

.github/workflows/image-release.yaml

This action runs on tags shaped like image-v1.2.3, and will build and push a container image to the GitHub Container Registry.

This action is super useful for optimizing the execution time of your action. By pre-building the image used in the Action, each invocation of your action can reference the image and not have to rebuild it for each invocation.

Once you push your first image you will also need to update the Container Registry to allow public access.

Lab Video

TODO: record and post the first lab walking through creation, execution and optimization

Lab Instructions

1. Click on "Use this template" on https://github.com/the-gophers/go-action, and create a repo of your own. I'm going to call mine "templated-action", make it public, and click "Create repository from template".
2. Clone your newly crated repo
3. Run go run . -h.
4. Run

   $ go run . --dryRun --message hello
   ::set-output name=sentMessage::hello

5. Checkout a new branch and let's make this our own GitHub Action. Run git checkout -b my-action
6. Update ./action.yml name, description, and author to something reasonable. The name field needs to be unique to others in the store.
7. When you are done with your changes, commit them, push your branch to GitHub, and open a pull request. In the PR, you should see the CI action run and complete successfully. LGTM! Let's merge these changes. Click the "Merge pull request" button, then delete the branch.
8. Check out main and pull down the latest changes from GitHub (git pull).
9. In test-repo click on Actions and run test-action with the inputs you desire. Navigate the UI to the running action and see that it built the action, built the Dockerfile and executed the entrypoint Go application. Also note how long it took to run the action. Using a Dockerfile will cause it to rebuild that image EACH time the action runs!. We can do better than that. More ahead.
10. Let's tag our first release (git tag v1.0.0) and push the tag (git push origin v1.0.0). This should create our first release in GitHub via the release action workflow.
11. Navigate to the v1.0.0 release and click edit. Within the release edit page, you should see "Publish this Action to the GitHub Marketplace". If you check that box, your action will now be publicly advertised to all of GitHub!
12. PSA: The rest of this is optional. If you don't care about your action going fast, stop right here.
13. Now we are going to make this FAST by pre-baking our container image. Go back to templated-action and edit ./github/workflows/release-image.yml. Change docker.pkg.github.com/owner/ to use your repo owner for owner. Commit and push the changes.
14. Now tag the repo with git tag image-v1.0.0 and then push the tag git push origin image-v1.0.0. This will kick off the image release build.
15. Replace image: Dockerfile with image: docker://ghcr.io/your-repo/your-image:1.0.0 replacing the repo and image name. Commit the changes and tag a new release of the Action as done in #12.
16. Rerun the continuous integration and see how much faster the action runs now that it doesn't have to rebuild the container image each time.

Contributions

Always welcome! Please open a PR or an issue, and remember to follow the Gopher Code of Conduct.