(GitHub) Action stations

Here are some notes I made on learning GitHub Actions:

There are some implicit environment variables. For instance, GITHUB_ENV (docs) is a temporary file that can hold environment variables like this:

          echo "ENVIRONMENT=develop" >> $GITHUB_ENV

This only appears to take an effect in the next run block.

In addition to these, there are contexts, which are "a way to access information about workflow runs, runner environments, jobs, and steps." For instance github.ref that refers to "the branch or tag ref that triggered the workflow run" (docs) and you use it with something like:

        if: endsWith(github.ref, '/develop')

To set up secrets you follow the instructions here. It asks you to go to the Settings tab on GitHub page. If you can't see it, you don't have permission to change them. You can reference these secrests like any other context. For example, to login to AWS:

      - name: Configure AWS Credentials
        uses: aws-actions/configure-aws-credentials@v1
        with:
          aws-access-key-id: '${{ secrets.AWS_ACCESS_KEY_ID }}'
          aws-secret-access-key: '${{ secrets.AWS_SECRET_ACCESS_KEY }}'
          aws-region: eu-west-2

Where aws-actions/configure-aws-credentials@v1 (and its ilk) are plugins to facilitate access to third party tools.

Contexts can also reference the output of actions. For example:

      - name: Login to Amazon ECR
        id: login-ecr
        uses: aws-actions/amazon-ecr-login@v1
      - name: 'Build, tag, and push image to Amazon ECR'
        env:
          ECR_REGISTRY: '${{ steps.login-ecr.outputs.registry }}'

Where login-ecr is an arbitrary ID but outputs.registry is part of the action's data structure.