Exploring Jobs in GitHub

Exploring Jobs in GitHub

In GitHub Actions, jobs are essential components of workflows. They define what tasks should be executed, where they run, and how they interact with other jobs. Let’s explore the details of jobs in GitHub workflows.

What are Jobs?

Definition:

A job is a sequence of steps that execute in the same runner environment.

Key Features:

• Each job runs independently by default.

• Jobs can run in parallel or sequentially, depending on dependencies.

• Jobs specify the virtual environment (runner) where they execute.

Syntax of Jobs

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jobs:
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  job_id:
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    name: Job Name
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    runs-on: runner-environment
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    needs: [other_job_id]
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    steps:
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     - name: Step Name
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        run: Command or Action

Key Elements

1. job_id: A unique identifier for the job. Example: build, test, deploy.

2. name: A descriptive name for the job (optional). Example: name: Build and Test Application.

3. runs-on: Specifies the runner environment for the job. Examples: ubuntu-latest, windows-latest, macos-latest.

4. needs: Specifies dependencies on other jobs, ensuring they run first.

5. steps: A list of actions or commands the job will execute.

Parallel vs Sequential Job Execution

Parallel Jobs (Default Behavior)

Jobs run in parallel unless dependencies are specified.

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jobs:
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  test:
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    runs-on: ubuntu-latest
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    steps:
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     - run: echo "Running tests"
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  lint:
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    runs-on: ubuntu-latest
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    steps:
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     - run: echo "Running linter"

Sequential Jobs (Using needs)

The needs keyword creates dependencies, ensuring jobs run in order.

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jobs:
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  build:
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    runs-on: ubuntu-latest
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    steps:
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     - run: echo "Building application"
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  test:
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    runs-on: ubuntu-latest
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    needs: build
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    steps:
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     - run: echo "Running tests"
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  deploy:
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    runs-on: ubuntu-latest
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    needs: test
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    steps:
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     - run: echo "Deploying application"

Specifying Runner Environments

The runs-on keyword determines the operating system and environment for the job.

• Common Environments:

  • ubuntu-latest (Linux)

  • windows-latest (Windows)

  • macos-latest (macOS)

• Self-Hosted Runners: For custom environments:

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  1
  runs-on: self-hosted
  

Defining Job Steps

Each job contains multiple steps.

Steps can include:

1. Use predefined actions.

2. Run custom shell commands.

Example:

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jobs:
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  example-job:
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    runs-on: ubuntu-latest
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    steps:
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     - name: Checkout code
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        uses: actions/checkout@v3
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     - name: Install dependencies
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        run: npm install
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     - name: Run tests
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        run: npm test

Environment Variables in Jobs

You can define environment variables at the job level, making them available to all steps.

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jobs:
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  example-job:
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    runs-on: ubuntu-latest
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    env:
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      NODE_ENV: production
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    steps:
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     - run: echo $NODE_ENV

Outputs in Jobs

Jobs can produce outputs that other jobs can use.

Example:

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jobs:
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  build:
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    runs-on: ubuntu-latest
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    outputs:
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      artifact-path: ${{ steps.upload.outputs.path }}
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    steps:
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     - id: upload
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        run: echo "::set-output name=path::build/artifact.zip"
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  deploy:
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    runs-on: ubuntu-latest
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    needs: build
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    steps:
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     - run: echo "Artifact path: ${{ needs.build.outputs.artifact-path }}"

Timeouts in Jobs

Jobs can be terminated if they exceed a specified duration using timeout-minutes.

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jobs:
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  example-job:
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    runs-on: ubuntu-latest
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    timeout-minutes: 10
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    steps:
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     - run: sleep 600

Job Strategies: Matrix Builds

The strategy keyword allows you to run jobs with different configurations (e.g., multiple versions of Node.js).

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jobs:
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  test:
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    runs-on: ubuntu-latest
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    strategy:
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      matrix:
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        node-version: [12, 14, 16]
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    steps:
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     - name: Set up Node.js
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        uses: actions/setup-node@v3
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        with:
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          node-version: ${{ matrix.node-version }}
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     - name: Run tests
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        run: npm test

Output:

Runs the test job three times, once for each Node.js version.

Job Permissions

Jobs can be restricted to certain permissions when accessing GitHub's API or repository contents.

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jobs:
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  example-job:
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    runs-on: ubuntu-latest
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    permissions:
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      contents: read
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    steps:
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     - run: echo "Restricted job permissions"

Common Use Cases for Jobs

1. Build and Test Pipelines: Compile and test code for multiple environments.

2. Deployment: Deploy applications after passing tests.

3. Static Analysis: Run linters and security checks.

4. Artifacts: Build and save artifacts for future jobs or workflows.

Summary

Jobs are flexible and powerful, enabling parallelization, dependencies, and tailored configurations for complex automation workflows.