Workflow Syntax

Reusability

Composite Actions

• On push to branch main, deploy to stage
• On a tag with suffix `-uat`, deploy to uat
• On a tag with suffix `-production`, deploy to production

 on:
  push:
    branches:
      - main
    tags:
      - *-uat
      - *-production

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - name: Deploy to stage
        if: contains(github.ref_name, 'main')
        run: ./deploy --environment stage

      - name: Deploy to uat
        if: endsWith(github.ref_name, '-uat')
        run: ./deploy --environment uat

      - name: Deploy to production
        if: endsWith(github.ref_name, '-production')
        run: ./deploy --environment production

• deploy-stage.yml
• deploy-uat.yml
• deploy-production.yml

In Engineering, every technical decision is about tradeoffs,  in this case, we are prioritizing reusability over simplicity, but that does not mean that if you prefer simplicity your approach is wrong. Choose the strategy that works best for you at the moment, and if the time comes, you can decide to keep it or change it - it's up to you.

name: 'Deployment'
description: 'Deploy to target environment'
runs:
  using: 'composite'
  steps:
    - name: Determine current environment using the current git ref
      shell: bash -leo pipefail {0}
      run: |
        set_env() { echo "$1" >> $GITHUB_ENV; export ENVIRONMENT=$1 }

        DEFAULT_BRANCH='main'
        CURRENT_REF=${GITHUB_REF_NAME}

        echo "Identified default branch : ${DEFAULT_BRANCH}"
        echo "Current git reference : ${CURRENT_REF}"

        if [[ "$CURRENT_REF" =~ .*-production$ ]]; then
          set_env "ENVIRONMENT=production"
        elif [[ "$CURRENT_REF" =~ .*-uat$ ]]; then
          set_env "ENVIRONMENT=uat"
        elif [[ "$CURRENT_REF" =~ "$DEFAULT_BRANCH" ]]; then
          set_env "ENVIRONMENT=stage"
        else
          echo "Error: Could not determine target environment."
          exit 1
        fi
    - name: Deploy to target environment
      run: ./deploy --environment ${{ env.ENVIRONMENT }}

• set_env() is a simple shell function that will append the first argument ($1) to the environment variable GITHUB_ENV. The GITHUB_ENV variable is a path to a file that the CI runner uses, so we are borrowing it so we can maintain the state of the env var we want to add between steps.
• DEFAULT_BRANCH is a constant with our trunk branch/ref as value.
• CURRENT_REF is also a constant with the current ref name as value.
• The if conditional block compares the CURRENT_REF with all the regular expressions we want to evaluate (*-production, *-uat and main), and then pushes the string `ENVIRONMENT=<env>` to GITHUB_ENV to save it. Now, the env var ENVIRONMENT will contain the target environment we want.
• Finally, we run the deployment task now using the context env (${{ env. }}) to access our recently saved variable ENVIRONMENT.

There is another way of setting the environment without the usage of the $GITHUB_ENV trick, which is to use Outputs.  I chose the simple shell script because it is tool-agnostic and you can use it outside of GitHub Actions simply changing `GITHUB_REF` to whatever variable contains the current git ref.

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Deploy to target environment
        uses: ./.github/actions/deploy

Mindset