GitHub Actions (S1E05)

Expression

Use expressions to programmatically set environment variables in workflow files and to access contexts.

#Example setting an environment variable
env:
  MY_ENV_VAR: ${{ <expression> }}

• The syntax for expression is ${{ <expression> }}

• Commonly used with the conditional if keyword in a workflow file to determine whether a step should run.

name: CI
on: push
jobs:
  prod-check:
    if: ${{ github.ref == 'refs/heads/main' }}
    runs-on: ubuntu-latest
    steps:
      - run: echo "Deploying to production server on branch $GITHUB_REF"

Status Check Functions

• use the following status check functions as expressions in if conditionals. A default status check of success() is applied unless you include one of these functions

success(): Returns true when all previous steps have succeeded.

steps:
  ...
  - name: The job has succeeded
    if: ${{ success() }}

always() : Causes the step to always execute, and returns true, even when canceled

if: ${{ always() }}

failure() : You can include extra conditions for a step to run after a failure, but you must still include failure() to override the default status check of success() that is automatically applied to if conditions that don't contain a status check function.

steps:
  ...
  - name: Failing step
    id: demo
    run: exit 1
  - name: The demo step has failed
    if: ${{ failure() && steps.demo.conclusion == 'failure' }}

cancelled(): Returns true if the workflow was canceled.

Logs

If the workflow logs do not provide enough detail to diagnose why a workflow, job, or step is not working as expected, you can enable additional debug logging.

Runner Diagnostic logging

Provides additional log files that contain information about how a runner is executing a job. Two extra log files are added

1. The runner process log: Includes information about coordinating and setting up runners to execute jobs.

2. The worker process log: Logs the execution of a job.

Enable

In the repository that contains the workflow set the variable/secret. : ACTIONS_RUNNER_DEBUG to true

The secret value takes precedence.

To download runner diagnostic logs, download the log archive of the workflow run. The runner diagnostic logs are contained in the runner-diagnostic-logs folder

Step Debug logging

Increases the verbosity of a job's logs during and after a job's execution.

Enable

In the repository that contains the workflow set the variable/secret. : ACTIONS_STEP_DEBUG to true

The secret value takes precedence.

From UI : We can rerun the job and select the Enable debug logging option. This will also enable runner diagnostic logs.

Cache

• To make your workflows faster and more efficient, you can create and use caches for dependencies and other commonly reused files.

• To cache dependencies for a job, you can use GitHub's cache action. The action creates and restores a cache identified by a unique key.

• The cache action will attempt to restore a cache based on the key you provide on a hit and creates one on a miss.

- name: Cache Gradle packages
  uses: actions/cache@v3
  with:
    name:
    path: |
      ~/.gradle/caches
      ~/.gradle/wrapper

Using expressions to create a key allows you to automatically create a new cache when dependencies change. Below examples creates a new cache when the packages in package-lock.json file change, or when the runner's operating system changes.

name: Caching with npm
on: push
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Cache node modules
        id: cache-npm
        uses: actions/cache@v3
        env:
          cache-name: cache-node-modules
        with:
          # npm cache files are stored in `~/.npm` on Linux/macOS
          path: ~/.npm
          key: ${{ runner.os }}-cache-${{ hashFiles('**/package-lock.json') }}

      - name: Install dependencies
        run: npm install
      - name: Build
        run: npm run build
      - name: Test
        run: npm test

Limits

Cache entries not accessed in over 7 days is removed. Upto 10Gb of cache is stored after which the old entries are deleted.