CircleCI Pipeline Patterns#

CircleCI pipelines are defined in .circleci/config.yml. The configuration model uses workflows to orchestrate jobs, jobs to define execution units, and steps to define commands within a job. Every job runs inside an executor – a Docker container, Linux VM, macOS VM, or Windows VM.

Config Structure and Executors#

A minimal config defines a job and a workflow:

version: 2.1

executors:
  go-executor:
    docker:
      - image: cimg/go:1.22
    resource_class: medium
    working_directory: ~/project

jobs:
  build:
    executor: go-executor
    steps:
      - checkout
      - run:
          name: Build application
          command: go build -o myapp ./cmd/myapp

workflows:
  main:
    jobs:
      - build

Named executors let you reuse environment definitions across jobs. The resource_class controls CPU and memory – small (1 vCPU/2GB), medium (2 vCPU/4GB), large (4 vCPU/8GB), xlarge (8 vCPU/16GB). Choose the smallest class that avoids OOM kills to keep costs down.