What is CircleCI?

CircleCI is a continuous integration and continuous delivery (CI/CD) platform that automates your development process, allowing you to build, test, and deploy code more efficiently. CircleCI's mission is to manage change so software teams can innovate faster and be more productive.

CI/CD Basics

Continuous Integration (CI) is a practice where developers integrate code into a shared repository frequently, usually multiple times per day. Each integration triggers automated tests and builds, allowing teams to detect and fix issues quickly.

Continuous Delivery (CD) is a practice that produces reliable releases to chosen development environments, such as staging or production branches.

Together, the CI/CD process helps developers release higher quality, more stable product.

How CircleCI Works

When you connect a software repository to CircleCI, every code change triggers automated tests in a clean container or virtual machine. CircleCI runs each job in a separate container or virtual machine and sends notifications of success or failure after tests complete.

Key Concepts

CircleCI uses a configuration-as-code approach. Your entire CI/CD process is defined in a single YAML file called config.yml, located in a .circleci folder at the root of your project. The main components of a CircleCI configuration are:

Pipelines: Represent the entirety of your configuration
Workflows: Orchestrate multiple jobs
Jobs: Run a series of steps that perform commands
Steps: Run commands (such as installing dependencies or running tests)

Setting Up CircleCI

To get started with CircleCI:

Create a .circleci directory in your project's root folder
Add a config.yml file to this directory
Define your build, test, and deployment processes in this file
Connect your repository to CircleCI

Here's a simple example of a CircleCI configuration:

version: 2.1
jobs:
  build:
    docker:
      - image: cimg/node:16.10
    steps:
      - checkout
      - run:
          name: Install dependencies
          command: npm install
      - run:
          name: Run tests
          command: npm test

This configuration defines a job called "build" that runs in a Docker container with Node.js, checks out your code, installs dependencies, and runs tests Viewport testing with Cypress.

Execution Environments

CircleCI supports various execution environments including:

Linux
macOS
Android
Windows

You can run your jobs in the cloud or on your own servers.

Advanced Features

CircleCI offers many advanced features including:

Orbs (reusable packages of configuration)
Contexts for sharing environment variables
Data persistence through artifacts, caches, and workspaces
Concurrency controls

If you'd like to learn more about any specific aspect of CircleCI, I'd be happy to provide more detailed information!

Additional Resources

What are the basics of CircleCI?