Introduction to GitHub actions

GitHub actions allow us to automate, customize and execute our software development workflows right in our repository. These workflows are composed of different tasks or actions that can be run automatically on certain events. This enables us to include Continuous Integration (CI) and continuous deployment (CD) capabilities and many other features directly in our repository.

Components of GitHub Actions

GitHub actions is an event-driven paradigm, meaning we can execute a series of commands after a certain event has occurred. We can create multiple workflows and multiple jobs in GitHub actions. As we see in the figure above, each and every job we create is running on a runner which separates virtual machines inside the GitHub server.

GitHub's action is composed of five main parts:

• Events - initiate or trigger an execution of a GitHub action workflow. An event may be an internal GitHub event (such as a push, a release, fork, issues, or a pull request), a scheduled event (triggered at a specific time, like a cron job), or an arbitrary external event (triggered by a webhook call to the GitHub API).

• Workflows - are composed of jobs that can be started by an event or by scheduling them to run at a specific time. Workflows assist in building, testing, releasing, or deploying our project to GitHub.

• Job - is a set of steps that run inside the same virtual machine runner, or inside a container. By default, they are executed in parallel, in other words, they don't wait for the previous job to be finished. Moreover, we can configure the jobs to run one after another if needed.

• Actions - in the workflow, we are going to specify our actions, which are the individual tasks that we use to achieve our goal. We can create our own actions, or use actions created by the GitHub community.

• Runners - is a virtual machine that runs a job. The runner is responsible for looking for the available jobs, then executes each job at a time. After the job is finished running, the runner reports the progress and logs of the job to GitHub. The runners hosted by GitHub consist of Ubuntu, Linux, Windows, and macOS.

Workflow syntax

To get started using GitHub Actions, we need to add a folder to the root of the GitHub repository.

.github/workflows

The workflow directory will contain the YAML files.

We can also go to the remote repository and go to the actions tab to create the workflow files directly.

YAML uses a fixed indentation scheme to represent relationships between data layers.

# your-repo-name/.github/workflows/first_workflow.yml

name: First Workflow    
                                         
on: push   
                                               
jobs:
                         
  first-job:                           
    name: Name of first step                    
    runs-on: ubuntu-latest                           
    steps:

      #step 1                           
      - name: Print a greeting                             
        run: echo Hi from our first workflow!

      #step 2 
      - uses: actions/[email protected]    
     
  second-job:
    strategy:
      matrix:
        runtimes: [10, 12, 14]
        os_version: [ubuntu-latest, windows-latest]
    runs-on: ${{ matrix.os_version}}
    steps:
      - uses: actions/setup-node@v3
        with:
          node-version: ${{ matrix.runtimes }}

The name of our workflow is First Workflow and our workflow is triggered by the push event. We have jobs that make the workflow.

In the first job, the following terms are laid out as follows:

• runs-on: the machine each job should run

• steps: the tasks each job should run

• run: the command the step should run

• uses: signature of the action we want to use from the GitHub marketplace

GitHub Actions allows us to automate the tasks to run on multiple versions of OS and runtimes. In the second job, a job will run for each possible combination of the variables. In this example, the workflow will run six jobs, one for each combination of the OS and version variables.

You don't need to understand all the details from the snippet as of now. We will cover them in future topics.

Conclusion

GitHub Actions consists of workflows that are stored in a git repository at the location .github/workflows. The workflows are generally triggered by certain events we specified in the workflow. After the workflow is triggered, the runner executes the jobs one by one. Each job consists of steps that are made up of actions that run as a part of the workflow.