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CircleCI Cheatsheet

1. Introduction:

  • CircleCI is a continuous integration and delivery platform that automates the build, test, and deploy processes, allowing for quick and efficient development workflows.

2. Key Concepts:

  • Job: A collection of steps to be executed in a build.
  • Step: A single command or script within a job.
  • Workflow: Defines the order of jobs and their dependencies.
  • Executor: Specifies the environment in which the job runs (e.g., Docker, Linux VM, macOS).

3. Basic .circleci/config.yml Example:

  • YAML Syntax:

    version: 2.1

jobs:
  build:
    docker:
      - image: circleci/node:14
    steps:
      - checkout
      - run: npm install
      - run: npm test

  deploy:
    docker:
      - image: circleci/node:14
    steps:
      - checkout
      - run: npm run deploy

workflows:
  version: 2
  build_and_deploy:
    jobs:
      - build
      - deploy

4. Executors:

  • Docker: Run jobs in Docker containers.

    docker:
  - image: circleci/node:14

  • Machine: Run jobs in a Linux VM.

    machine:
  image: ubuntu-2004:202101-01

  • macOS: Run jobs on macOS for iOS builds.

    macos:
  xcode: "12.4.0"

5. Reusable Configurations:

  • Commands: Reuse steps across multiple jobs.

    commands:
  setup:
    steps:
      - checkout
      - run: npm install

jobs:
  build:
    docker:
      - image: circleci/node:14
    steps:
      - setup
      - run: npm test

  • Executors: Reuse the environment configuration.

    executors:
  node-executor:
    docker:
      - image: circleci/node:14

jobs:
  build:
    executor: node-executor
    steps:
      - checkout
      - run: npm install

6. Caching and Artifacts:

  • Caching: Speed up builds by caching dependencies.

    - restore_cache:
    keys:
      - v1-dependencies-{{ checksum "package-lock.json" }}
- save_cache:
    paths:
      - node_modules
    key: v1-dependencies-{{ checksum "package-lock.json" }}

  • Artifacts: Save build outputs and other data for later use.

    - store_artifacts:
    path: ./build
    destination: build_output

7. Workflows:

  • Sequential Jobs: Define jobs that run in sequence.

    workflows:
  version: 2
  build_and_deploy:
    jobs:
      - build
      - deploy

  • Parallel Jobs: Run jobs in parallel to speed up pipeline execution.

    workflows:
  version: 2
  test-and-deploy:
    jobs:
      - test
      - deploy

8. Environment Variables:

  • Project-level Variables: Set environment variables in the CircleCI project settings.

  • Context Variables: Use contexts to securely store and manage environment variables.

  • Job-level Variables:

    jobs:
  build:
    docker:
      - image: circleci/node:14
    environment:
      NODE_ENV: production

9. Advanced CircleCI Features:

  • Orbs: Reusable packages of CircleCI configuration that make it easy to integrate with third-party tools.

    orbs:
  aws-s3: circleci/aws-s3@4.2.0

jobs:
  deploy:
    steps:
      - aws-s3/copy:
          from: "build/"
          to: "s3://my-bucket/"

  • Conditional Steps: Run steps conditionally based on the success or failure of previous steps.

    - run:
    name: Deploy only if tests pass
    command: ./deploy.sh
    when: on_success

10. Best Practices:

  • Parallelism: Use parallelism to reduce build times by running tests and other tasks simultaneously.
  • Modular Configurations: Break down your CircleCI configuration into reusable components with orbs, commands, and executors.
  • Effective Caching: Cache dependencies effectively to reduce build times, but remember to invalidate caches when necessary to avoid stale dependencies.