|
| 1 | +--- |
| 2 | +applyTo: ".github/workflows/*.yml,.github/workflows/*.yaml" |
| 3 | +--- |
| 4 | +# CI/CD Conventions — GitHub Actions Workflows |
| 5 | + |
| 6 | +## YAML Style |
| 7 | + |
| 8 | +- Indent with **2 spaces** (no tabs) |
| 9 | +- Every workflow, job, and step must have a `name:` field that clearly describes its purpose |
| 10 | +- Group related steps logically; separate unrelated groups with a blank line |
| 11 | +- Comments (`#`) are encouraged for non-obvious decisions (e.g., why `fail-fast: false` is set, what a cron expression means) |
| 12 | + |
| 13 | +## Workflow Structure |
| 14 | + |
| 15 | +### Triggers |
| 16 | + |
| 17 | +- Declare `on:` triggers explicitly; avoid bare `on: push` without branch filters on long-running or expensive jobs |
| 18 | +- Prefer `workflow_call` for shared build logic (see `build.yml`) to avoid duplicating steps across workflows |
| 19 | +- Document scheduled triggers (`cron:`) with a human-readable comment: |
| 20 | + |
| 21 | +```yaml |
| 22 | +schedule: |
| 23 | + - cron: '0 2 * * *' # run at 2 AM UTC daily |
| 24 | +``` |
| 25 | +
|
| 26 | +### Jobs |
| 27 | +
|
| 28 | +- Express all inter-job dependencies with `needs:` — never rely on implicit ordering |
| 29 | +- Use job `outputs:` + step `id:` to pass structured data between jobs (see `get_default_envs` in `build.yml`) |
| 30 | +- Set `fail-fast: false` on matrix builds so that a single failing environment does not cancel others |
| 31 | + |
| 32 | +### Runners |
| 33 | + |
| 34 | +- Pin to a specific Ubuntu version (`ubuntu-22.04`, `ubuntu-24.04`) rather than `ubuntu-latest` for reproducible builds |
| 35 | +- Only use `ubuntu-latest` in jobs where exact environment reproducibility is not required (e.g., trivial download/publish steps) |
| 36 | + |
| 37 | +### Tool and Language Versions |
| 38 | + |
| 39 | +- Pin tool versions explicitly: |
| 40 | + ```yaml |
| 41 | + python-version: '3.12' |
| 42 | + ``` |
| 43 | +- Do not rely on the runner's pre-installed tool versions — always install via a versioned setup action |
| 44 | + |
| 45 | +### Caching |
| 46 | + |
| 47 | +- Always cache package managers and build tool directories when the job installs dependencies: |
| 48 | + ```yaml |
| 49 | + - uses: actions/cache@v4 |
| 50 | + with: |
| 51 | + path: ~/.cache/pip |
| 52 | + key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }} |
| 53 | + restore-keys: | |
| 54 | + ${{ runner.os }}-pip- |
| 55 | + ``` |
| 56 | +- Include the environment name or a relevant identifier in cache keys when building multiple targets |
| 57 | + |
| 58 | +### Artifacts |
| 59 | + |
| 60 | +- Name artifacts with enough context to be unambiguous (e.g., `firmware-${{ matrix.environment }}`) |
| 61 | +- Avoid uploading artifacts that will never be consumed downstream |
| 62 | + |
| 63 | +--- |
| 64 | + |
| 65 | +## Security |
| 66 | + |
| 67 | +### Permissions — Least Privilege |
| 68 | + |
| 69 | +Declare explicit `permissions:` blocks. The default token permissions are broad; scope them to the minimum required: |
| 70 | + |
| 71 | +```yaml |
| 72 | +permissions: |
| 73 | + contents: read # for checkout |
| 74 | +``` |
| 75 | + |
| 76 | +For jobs that publish releases or write to the repository: |
| 77 | + |
| 78 | +```yaml |
| 79 | +permissions: |
| 80 | + contents: write # create/update releases |
| 81 | +``` |
| 82 | + |
| 83 | +A common safe baseline for build-only jobs: |
| 84 | + |
| 85 | +```yaml |
| 86 | +permissions: |
| 87 | + contents: read |
| 88 | +``` |
| 89 | + |
| 90 | +### Supply Chain — Action Pinning |
| 91 | + |
| 92 | +**Third-party actions** (anything outside the `actions/` and `github/` namespaces) should be pinned to a specific release tag. Branch pins (`@main`, `@master`) are **not allowed** — they can be updated by the action author at any time without notice: |
| 93 | + |
| 94 | +```yaml |
| 95 | +# ✅ Acceptable — specific version tag. SHA pinning recommended for more security, as @v2 is still a mutable tag. |
| 96 | +uses: softprops/action-gh-release@v2 |
| 97 | +
|
| 98 | +# ❌ Not acceptable — mutable branch reference |
| 99 | +uses: andelf/nightly-release@main |
| 100 | +``` |
| 101 | + |
| 102 | +SHA pinning (e.g., `uses: someorg/some-action@abc1234`) is the most secure option for third-party actions; it is recommended when auditing supply-chain risk is a priority. At minimum, always use a specific version tag. |
| 103 | + |
| 104 | +**First-party actions** (`actions/checkout`, `actions/cache`, `actions/upload-artifact`, etc.) pinned to a major version tag (e.g., `@v4`) are acceptable because GitHub maintains and audits these. |
| 105 | + |
| 106 | +When adding a new third-party action: |
| 107 | +1. Check that the action's repository is actively maintained |
| 108 | +2. Review the action's source before adding it |
| 109 | +3. Prefer well-known, widely-used actions over obscure ones |
| 110 | + |
| 111 | +### Credentials and Secrets |
| 112 | + |
| 113 | +- Use `${{ secrets.GITHUB_TOKEN }}` for operations within the same repository — it is automatically scoped and rotated |
| 114 | +- Never commit secrets, tokens, or passwords into workflow files or any tracked file |
| 115 | +- Never print secrets in `run:` steps, even with `echo` — GitHub masks known secrets but derived values are not automatically masked |
| 116 | +- Scope secrets to the narrowest step that needs them using `env:` at the step level, not at the workflow level: |
| 117 | + |
| 118 | +```yaml |
| 119 | +# ✅ Scoped to the step that needs it |
| 120 | +- name: Create release |
| 121 | + uses: softprops/action-gh-release@v2 |
| 122 | + with: |
| 123 | + token: ${{ secrets.GITHUB_TOKEN }} |
| 124 | +
|
| 125 | +# ❌ Unnecessarily broad |
| 126 | +env: |
| 127 | + GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} |
| 128 | +``` |
| 129 | + |
| 130 | +- Personal Access Tokens (PATs, stored as repository secrets) should have the minimum required scopes and should be rotated periodically |
| 131 | + |
| 132 | +### Script Injection |
| 133 | + |
| 134 | +`${{ }}` expressions are evaluated before the shell script runs. If an expression comes from untrusted input (PR titles, issue bodies, branch names from forks), it can inject arbitrary shell commands. |
| 135 | + |
| 136 | +**Never** interpolate `github.event.*` values directly into a `run:` step: |
| 137 | + |
| 138 | +```yaml |
| 139 | +# ❌ Injection risk — PR title is attacker-controlled |
| 140 | +- run: echo "${{ github.event.pull_request.title }}" |
| 141 | +
|
| 142 | +# ✅ Safe — value passed through an environment variable |
| 143 | +- env: |
| 144 | + PR_TITLE: ${{ github.event.pull_request.title }} |
| 145 | + run: echo "$PR_TITLE" |
| 146 | +``` |
| 147 | + |
| 148 | +This rule applies to any value that originates outside the repository (issue bodies, labels, comments, commit messages from forks). |
| 149 | + |
| 150 | +### Pull Request Workflows |
| 151 | + |
| 152 | +- Workflows triggered by `pull_request` from a fork run with **read-only** token permissions and no access to repository secrets — this is intentional and correct |
| 153 | +- Do not use `pull_request_target` unless you fully understand the security implications; it runs in the context of the base branch and *does* have secret access, making it a common attack surface |
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