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GitHub Actions workshop

Requirements

  • A GitHub account, with a functioning SSH-key or password setup
  • Available GitHub action minutes and storage space (included in free tier)

The tasks in the workshop can be done using only the built-in GitHub editor. However, in order to learn about supporting tooling, and simplify some tasks, the workshop will assume you've installed the following tools:

Getting started

Start by creating your own fork of this repository. If you've installed gh you can run gh repo fork --clone bekk/github-actions-workshop to create your own fork of this repository and clone it to your machine. Run gh auth first if you're using gh for the first time. Otherwise, use the GitHub UI to fork this repository. If you're reading the tasks in the browser, use the forked repo so that relative links work correctly.

This repository contains a simple go app. You do not need to know go, nor use any Golang tooling. We will, unless explicitly specified otherwise, only modify files in the special .github/ directory.

Tip

The Workflow syntax for GitHub Actions is handy if you're not sure how something works.

Your first workflow

  1. We'll start with a simple workflow. Create the file .github/workflows/test.yml with the following content:

    # The "display name", shown in the GitHub UI
name: Build and test

# Trigger, run on push on any branch
on:
  push:

jobs:
  test: # The 'build' job
    name: "Build application"
    runs-on: 'ubuntu-latest'
    steps:
      # Step to print a simple message
      - run: echo "Hello world"

    .github/workflows/ is a special directory where all workflows should be placed.

  2. (Optional) Before committing and pushing, run actionlint from the repository root. It should run with a zero (successful) exit code and no output, since the workflow file is without errors. Try again with actionlint --verbose and verify the output to confirm that it found your file. By default, actionlint scans all files in .github/workflows/

  3. Commit and push the workflow to your fork. In the GitHub UI, navigate to the "Actions" tab, and verify that it runs successfully.

Note

How does this work?

Let's break down the workflow file.

  • name: is only used for display in the GitHub UI
  • on: specifies triggers - what causes this workflow to be run
  • jobs: specifies each job in the workflow. A job runs on a single virtual machine with a given OS (here: ubuntu-latest), and the steps share the environment (filesystem, installed tools, environment variables, etc.). Different jobs have separate environments.
  • steps: run sequentially, and might run shell scripts or an action (a reusable, pre-made piece of code). Each step can run conditionally. If a step fails, all later steps fail by default. Creating steps to do e.g. cleanup in error situations is possible.

Build and test the application

  1. Let's use some pre-made actions to checkout our code, and install Golang tooling. Replace the "hello world" step with the following steps:

          # Checkout code
      - uses: actions/checkout@v4

      # Install go 1.21
      - name: Setup go
        uses: actions/setup-go@v4
        with: # Specify input variables to the action
          go-version: '1.21.x'

      # Shell script to print the version
      - run: go version

  2. Again, run actionlint before you commit and push. Verify that the correct version is printed.

  3. Continue by adding steps to build and test the application:

      - name: Build
    run: go build -v ./...

  - name: Test
    run: go test ./...

  4. Verify that the workflow fails if the build fails (create a syntax error in any file). Separately, verify that the workflow fail when the tests are incorrect (modify a test case in internal/greeting/greet_test.go).

Building a Docker image

  1. A Dockerfile defining the application image exists in the root directory. To do a container-based deploy we'll use the actions provided by Docker to build the image. Create .github/workflows/build.yml with the following content:

    on:
  push

jobs:
  build:
    runs-on: 'ubuntu-latest'
    steps:
    - uses: actions/checkout@v4
    - name: Set up Docker Buildx
      uses: docker/setup-buildx-action@v3

    - name: Use lowercase repository name as docker image name
      run:
        export REPOSITORY=${{ github.repository }}
        echo "DOCKER_IMAGE_NAME=${REPOSITORY@L}" >> "$GITHUB_ENV"

    - name: Build and push Docker image
      uses: docker/build-push-action@v5
      with:
        push: false
        tags: ghcr.io/${{ env.DOCKER_IMAGE_NAME }}:latest

Note

The ${{ <expression> }} syntax is used to access variables, call functions and more. You can read more in the documentation.

In this case, ${{ github.repository }} is a variable from the github context and will be <user-or-org>/<repo-name>. github.repository may contain uppercase letters, but the a Docker image must be all lower case, so we transform the repository using a shell parameter expansion in a separate step. The lower-cased repository name is set as an environment variable.

GitHub has a list of default environment variables. In this case, we're defining our own environment variable by writing to the special $GITHUB_ENV file. When setting environment variables this way, it will be available in subsequent steps.

It is also possible to define environment variables by using an env property at the workflow, job or step scopes. This is usually simpler, when possible.

  1. Push and verify that the action runs correctly.

  2. In order to push the image, we will need to set up permissions. With packages: write you allow the action to push images to the GitHub Container Registry (GHCR). You can set it at the top-level, for all jobs in the workflow, or for a single job:

    jobs:
  build:
    permissions:
      packages: write
    # ... runs-on, steps, etc

  3. We'll have to add a step the docker/login-action@v3 action to login to GHCR, before we push it. Add the following step before the build and push step:

          - name: Login to GitHub Container Registry
        uses: docker/login-action@v3
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ github.token }}

Note

The github.token (often referred to as GITHUB_TOKEN) is a special token used to authenticate the workflow job. Read more about it here in the documentation.

  1. Finally, modify the build and push step. Set push: true to make the action push the image after it's built.

  2. Push the changes and make sure the workflow runs successfully. This will push the package to your organization's or your own package registry. The image should be associated with your repo as a package (right-hand side on the main repository page).

Parallel jobs

Jobs in the same workflow file can be run in parallel if they're not dependent on each other.

  1. We also want to lint the app code. In order to get faster feedback, we can create a separate lint-job in our test.yml workflow file. Create a new job in test.yml for linting called lint, which contains the following step:

          # Also add checkout and setup go steps here, like in previous tasks
      - name: Verify formatting
        run: |
          no_unformatted_files="$(gofmt -l $(git ls-files '*.go') | wc -l)"
          exit "$no_unformatted_files"

  2. Push the code and verify that the workflow runs two jobs successfully.

Triggering workflows

Workflows can be triggered in many different ways and can be grouped into four type of events:

  • Repository related events
  • External events
  • Scheduled triggering
  • Manual triggering

Repository related events are the most common and are triggered when something happens in the repository. External events and scheduled triggers are not covered in this workshop, but it is nice to know that it is possible. Some example triggers:

on: push # Triggers when a push is made to the repository
on: pull_request # Triggers when a pull request is opened or changed
on: workflow_dispatch # Triggers when a user manually requests a workflow to run

Some events have filters that can be applied to limit when the workflow should run. For example, the push-event has a branches-filter that can be used limit the workflow to only run if it is on a specific branch (or branches)

on:
  push:
    branches:
      - main
      - 'releases/**'  # Wildcard can be used to limit to a specific set of branches
  1. Rewrite the docker build workflow build.yml to only be done on main and rewrite the build and lint workflow test.yml to only run on PR changes. Push the changes to main-branch and observe that only the build-workflow is executed.
  2. Create a new feature branch, add a new commit with a dummy change (to any file) and finally create a PR to main. Verify that the test.yml workflow is run on the feature branch. Merge the PR and verify that the build.yml-workflow is only run on the main-branch.
  3. Update the test.yml workflow and add the event for triggering the workflow manually. Make sure to push the change to main-branch.
  4. Go to the GitHub Actions page of the workflow and verify that the workflow can be run manually. A Run workflow button should appear to enable you to manually trigger the workflow.

Note

In order for the Run workflow-button to appear the workflow must exist on the default branch, typically the main-branch

Reusable workflows

Reusable workflows makes it possible to avoid duplication and reuse common workflow-functionality. They can be shared within a single repository or by the whole organization.

To pass information to a shared workflow you should either use the vars-context or pass information directly to the workflow. The variables for the vars-context can be found here.

Reusable workflows use the workflow_call-trigger. A simple reusable workflow that accepts a config value as input look like this:

on:
  workflow_call:
    inputs:
      config-value:
        required: true
        type: string

Calling a reusable workflow

To call a reusable workflow in the same repository:

jobs:
  call-workflow-passing-data:
    uses: ./.github/workflows/my-reusable-workflow.yml
    with:
      config-value: 'Some value'
  1. Create a reusable workflow that runs the test-job specified in test.yml and modify test.yml to use the reusable workflow for running the tests
  2. Create a reusable workflow for the the code in build.yml and use a input-parameter to determine if the image should be pushed or not.

Note

A limitation of reusable workflows is that you have to run it as a single job, without the possibility to run additional steps before or after in the same environment. If you want to create reusable code that runs in the same environment, you can create a custom action which we will look at later in the workshop.

Deploying to environment

For the purposes of this workshop, we'll not actually deploy to any environment, but create a couple of GitHub environments to demonstrate how deployments would work. You can use environments to track deploys to a given environment, and set environment-specific variables required to deploy your application.

Example of a deployment job to an environment:

jobs:
  deployment:
    runs-on: ubuntu-latest
    environment: production # This environment applies to all steps in this job
    steps:
      - name: deploy

  1. Navigate to Settings > Environments and create two new environments: test and production. For each environment set a unique environment variable, WORKSHOP_ENV_VARIABLE.

  2. Create a new workflow in .github/workflows/deploy.yml. This workflow should trigger on workflow_dispatch, and take three inputs: environment of type environment, and the strings imageName and digest. It should have a single job, deploy, and here it should just "fake" the deploy by printing the imageName and digest. All inputs should be required set required to true. The job should run in context of the input environment and print the environment variable ${{ vars.WORKSHOP_ENV_VARIABLE }} configured for the environment.

  3. Push the new workflow (to main-branch), and verify that you get a dropdown to select the environment when you trigger it, and that the value of WORKSHOP_ENV_VARIABLE is printed for the chosen environment.

Job dependencies

Jobs can depend on each other. We'll now create a workflow that builds, then deploys the Docker image to test and production, in that order.

  1. Modify the deploy.yml to make it reusable by adding a workflow_call trigger. It should have the same inputs as the workflow_dispatch trigger.

  2. Modify your reusable build action to propagate outputs. You'll need to add an id: build-push to the step that builds the image. Then, you can add an outputs object property to the job and the workflow.

    To get the correct outputs from the docker/build-push-action action, you should use fromJson(jobs.build.outputs.metadata)['image.name'] and jobs.build.outputsdigest outputs from the build-push action as imageName and digest respectively. You can read more about the fromJson expression in the documentation.

    Take a look at the documentation for a complete example of outputs for a reusable workflow.

  3. Expand your (non-reusable) build workflow with a couple of more jobs: deploy-test and deploy-production. These jobs should reuse the deploy.yml workflow, use imageName and digest outputs from the build job and use correct environments. You have to specify needs for the deploy jobs, take a look at the needs context and corresponding example.

  4. Push the workflow, and verify that the jobs run correctly, printing the correct docker image specification and environment variable. The deploy-test job should also finish before the production-test job starts.

Branch protection rules

Many teams want require code reviews, avoid accidental changes, run tests or ensure that the formatting is correct on all new code before merging. These restrictions can be done using branch protection rules.

You can find branch protections rules by going to Settings > Branches (requires repository administrator privileges). Let's create a branch protection rule for the main branch:

  1. Set main as the branch name pattern.

  2. Set the setting "Require a pull request before merging", and untick the "Require Approvals" sub-setting.

  3. Set the setting "Require status checks to pass before merging", and make sure that both the jobs for linting and testing are selected.

  4. Set the "Do not allow bypassing the above settings" setting to disallow administrator overrides, and finally click "Create".

  5. Create a change (e.g. text change in the README). Try pushing the change from your local computer directly to main and verify that it gets rejected (if you're using the GitHub UI, you will be forced to create a branch).

  6. Create a change on a separate branch, push it and create a PR. Verify that you cannot merge it until the status checks have passed.

  7. Optionally, turn off the "Require a pull request before merging" and/or "Do not allow bypassing the above settings" settings before you continue, to simplify the rest of the workshop. Read through the list of settings once more and research options you want to know more about in the documentation.

Tip

Branch protection rules will disallow force pushes for everyone, including administrators, by default, but this can be turned on again in the settings.

Extra: Composite actions

Composite actions is a way to create reusable actions. Read through the composite action documentation and try creating one.

When creating an action in the same repository as your other workflows, it's customary to put it in .github/actions/. E.g., for a build-image composite action you would create .github/action/build-image/action.yml. You can then refer to it with uses: ./.github/actions/build-image in your workflow.

Other extras:

Control concurrent workflows or jobs

The default behavior of GitHub Actions is to allow multiple jobs or workflows to run concurrently.

If you have frequent deploys to an environment this can be a problem because you typically don't want to have multiple deploys to the same environment happening at the same time.

The solution is to control the concurrency of a job or workflow by specifying a concurrency group:

concurrency:
  group: prod-deploy
  cancel-in-progress: true/false

Github Actions ensures that jobs or workflows with the same key are not allowed run at the same time. If cancel-in-progress is false the workflow or jobs will run sequentially.

  1. Change the deploy.yml workflow to ensure that deploys to the same environment is done sequentially

Manual approval before production deploy

You can enforce manual approval before production deploy. Navigate to Settings > Environments and enable "Required reviewers" for the production environment.

Only trigger build on application source changes

You can ensure that certain actions only run when the code changes. E.g., you might not want or need all actions to run for a change in README.md. Take a look at the documentation to see how you can modify the push trigger.

Production deploy for main branch only

You can use conditions to control wheter a job or step should run. Change your actions so that only the main branch can be deployed to production. Other branches can still be deployed to the test environment.

Tip

You will likely need the github.ref_name from the github context to do this.

Caching docker image layers

GitHub Actions has caching functionality. You can save build time by caching Docker image layers. Take a look at Docker's documentation for guidance.

Environment secrets

TODO