Circleci Skill for Claude

CircleCI Configuration Guide

Critical Rules

• No long inline scripts — script logic for any language must not be written inline in .circleci/config.yml if the script has complicated flow control. Complicated scripts belong in bin/.
• Scripts live in bin/ — every script called from CircleCI must exist as a file in the bin/ directory with an appropriate extension (e.g. bin/my-script.sh, bin/my-script.py).
• Pin all versions — never use latest or unpinned tags for Docker images or installed tools. Always specify an exact version to prevent supply chain vulnerabilities and ensure reproducible builds.

Script Organization

Scripts invoked by CircleCI jobs must be committed to the repository under bin/ so they can be:

• Linted and reviewed like any other source file
• Tested and run locally without needing CI
• Reused across multiple jobs or workflows

# ✅ CORRECT — call a script from bin/
steps:
  - run:
      name: Build Helm chart
      command: bin/build-helm-chart.sh

# ❌ WRONG — inline shell logic in the CircleCI config
steps:
  - run:
      name: Build Helm chart
      command: |
        helm package .
        mv airflow-*.tgz /tmp/chart/

Config Generation Pipeline

.circleci/config.yml is never edited directly — it is a generated file (its header says so). It is produced by rendering the Jinja2 template .circleci/config.yml.j2 via bin/generate_circleci_config.py:

# Regenerate config.yml from the template
bin/generate_circleci_config.py        # or: uv run bin/generate_circleci_config.py

The generator injects a small set of computed variables into the template at render time:

• kube_versions — read from metadata.yaml (test_k8s_versions)
• executors — ["CeleryExecutor", "LocalExecutor", "KubernetesExecutor"]
• machine_image_version — the CircleCI machine image (pinned in the generator script)
• ci_runner_version — derived from the current year-month

Always edit .circleci/config.yml.j2 (or bin/generate_circleci_config.py for the injected values), then regenerate and commit both the template and the generated config.yml. The chart's K8s test matrix is driven entirely by metadata.yaml, so adding/removing a tested Kubernetes version is a metadata.yaml edit followed by a regenerate.

> CI runs only on kind (vanilla Kubernetes), never OpenShift. The matrix is kube_versions × executors on kind. OpenShift-specific behavior (e.g. openshift.enabled=true SCC / UID-range handling, PINF-559) is not exercised in CI and must be verified manually — a change can be green in CI and still break only on OpenShift. See CLAUDE.md.

Version Pinning

Always pin exact versions for Docker images and any tools installed during a job. Using latest or loose tags introduces supply chain risk and makes builds non-reproducible.

Pinned versions that the generator controls (e.g. machine_image_version) live in bin/generate_circleci_config.py, and the Kubernetes test versions live in metadata.yaml — keep them there rather than scattered inline so they are easy to audit and update in one place. Include a link near each version declaration to where released versions can be found, so updating doesn't require searching online.

# ✅ CORRECT — version pinned in bin/generate_circleci_config.py
machine_image_version = "ubuntu-2204:2025.09.1"  # https://circleci.com/developer/machine/image/ubuntu-2204

# ✅ CORRECT — version referenced via an injected variable in config.yml.j2
machine:
  image: { { machine_image_version } }

# ❌ WRONG — unpinned image
docker:
  - image: cimg/python:latest

# ✅ CORRECT — pinned tool version installed via a bin/ script
- run:
    name: Install CI tools
    command: bin/install-ci-tools

# ❌ WRONG — unversioned tool install piped straight from the internet
- run:
    name: Install helm
    command: curl https://raw.githubusercontent.com/helm/helm/main/scripts/get-helm-3 | bash