CI/CD Patterns

Patterns for GitHub Actions, PR automation, and deployment workflows.

When to Use

• Setting up or fixing GitHub Actions workflows
• Automating PR checks (lint, test, build)
• Configuring deployment pipelines
• Monitoring PR status and retrying flaky CI
• Setting up multi-environment deployment (dev, staging, prod)

GitHub Actions --- Common Patterns

Basic CI Workflow

name: CI
on:
  push:
    branches: [main, develop]
  pull_request:
    branches: [main, develop]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Run tests
        run: ./gradlew test

PR Check Workflow

name: PR Check
on: pull_request

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: ./gradlew ktlintCheck

  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: ./gradlew test

  build:
    runs-on: ubuntu-latest
    needs: [lint, test]
    steps:
      - uses: actions/checkout@v4
      - run: ./gradlew build

PR Babysitting Pattern

Monitor a PR through CI, handle common failures:

1. Check CI status --- gh pr checks <number>
2. Identify failure type --- flaky test, lint error, build failure
3. Fix and push --- for lint/build errors, fix locally and push
4. Retry flaky tests --- re-run the workflow: gh run rerun <run-id> --failed
5. Resolve merge conflicts --- rebase onto target branch
6. Enable auto-merge --- gh pr merge <number> --auto --squash

See workflows.md for ready-to-use GitHub Actions YAML templates.

Deployment Checklist

Before deploying:

• All CI checks pass
• No merge conflicts
• Database migrations reviewed (if any)
• Environment variables set in target environment
• Rollback plan identified

Gotchas

• Caching saves minutes per run. Always cache dependencies (actions/cache or actions/setup-java with cache). A cold Gradle build takes 3-5 minutes, cached takes 30 seconds.
• needs: creates sequential dependencies. Without it, all jobs run in parallel. Use needs: [lint, test] to make build wait for checks.
• Secret names are case-sensitive. secrets.DB_PASSWORD and secrets.db_password are different. Match the exact name from Settings > Secrets.
• Don't use actions/checkout@v3 --- use v4. v3 uses Node 16 which is deprecated. v4 uses Node 20.
• Flaky tests need investigation, not just retry. If you re-run a workflow more than twice for the same test, fix the test. Common causes: race conditions, time-dependent assertions, shared test state.
• Force-pushing during CI review resets the check suite. Wait for CI to finish before force-pushing, or you'll waste runner minutes.

Rules

• Every PR must pass CI before merge
• Don't skip CI checks ([skip ci]) unless it's docs-only
• Keep workflows under 10 minutes total
• Use matrix builds for multi-version testing
• Store secrets in GitHub Secrets, never in code