CircleCI
CircleCI is a hosted CI/CD platform built around fast pipelines and reusable configuration. You define everything in .circleci/config.yml, and CircleCI runs your jobs across Docker, Linux, macOS, or Windows executors — with orbs packaging common setups so you don't reinvent them.
It's a strong choice when you want managed CI with first-class caching and parallelism, and the flexibility to standardize config across many repositories.
TL;DR
- Pipelines are defined in
.circleci/config.yml. - Workflows orchestrate jobs; executors define the environment.
- Orbs are reusable config packages — standardize across projects.
- Use caching to keep builds fast; keep credentials scoped.
Quick Example
A workflow runs a test job, then a deploy job that depends on it and is filtered to main:
Core Concepts
- Jobs — units of work (a set of steps).
- Workflows — orchestrate jobs with ordering, dependencies, and filters.
- Executors — the environment a job runs in (Docker image, machine, macOS).
- Orbs — reusable, shareable config packages (e.g. a Node orb).
Best Practices
- Run tests on pull requests; separate build/test/deploy into a workflow.
- Cache dependency installs (keyed on a lockfile) to speed runs.
- Use orbs to standardize common steps across repos.
- Keep credentials scoped to the jobs/contexts that need them; never print secrets.
Common Mistakes
Incorrect caching → stale builds
Pipelines tied to implicit state
FAQ
What are orbs?
Orbs are reusable, versioned packages of CircleCI config — jobs, commands, and executors — that you import into your pipeline. They let you standardize common tasks (e.g. setting up Node, deploying to AWS) across projects instead of copy-pasting YAML.
What's the difference between jobs and workflows?
A job is a single unit of work (a sequence of steps in an executor). A workflow orchestrates multiple jobs — defining order, dependencies (requires), parallelism, and branch filters. Workflows are how you build multi-stage pipelines.
How do I speed up CircleCI builds?
Cache dependencies keyed on your lockfile, run independent jobs in parallel within a workflow, use right-sized resource classes, and split slow test suites. Good caching usually delivers the biggest win.
CircleCI or GitHub Actions?
Both are capable hosted CI platforms. GitHub Actions is the natural default if you're on GitHub. CircleCI appeals when you want its orb ecosystem, fine-grained executors/resource classes, or are integrating across multiple SCMs. Choose by ecosystem fit.
Related Topics
- CI/CD Pipelines — The fundamentals
- GitHub Actions — Common alternative
- Testing — What to automate
- Docker — Executor images
- DevOps — The broader practice