CircleCI and Docker - How it is done?

[Voxelghiest]

A unique feature to CircleCI is the ability to run a job in any Docker image. CircleCI provides a number of pre-built Docker images tailored to specific programming languages or CI/CD needs.

You can specify using a Docker image as part of any CircleCI job. The syntax is as follows:

version: 2.1

jobs:
  say-hello-docker:
    docker:
      - image: cimg/node:18.0.0

The above example uses the pre-built Node image, which provides access to Node.js and a number of commonly used helper tools. Additional tools can also be installed as part of the job's steps, if needed.

For a complete CircleCI workflow, demonstrating both a Docker and machine job executor, copy the following into your config.yml file:

# Use the latest 2.1 version of CircleCI pipeline process engine.
# See: https://circleci.com/docs/2.0/configuration-reference
version: 2.1

# Define a job to be invoked later in a workflow.
# See: https://circleci.com/docs/2.0/configuration-reference/#jobs
jobs:
  say-hello-docker:
    # Uses a Docker image to run the job in. 
    # There are a number of useful Docker images for different programming languages.
    # You can specify an image from Dockerhub or use one of the Convenience Images from CircleCI's Developer Hub.
    # See: https://circleci.com/docs/2.0/executor-types/#using-docker
    docker:
      - image: cimg/node:18.0.0
    # Add steps to the job
    # See: https://circleci.com/docs/2.0/configuration-reference/#steps
    steps:
      - checkout
      - run:
          name: "Say Hello From Docker"
          command: "echo Hello from docker!"
      - run: node --version

  say-hello-machine:
    # Uses a Linux machine instead of a Docker image. You still have to specify which version of Ubuntu to use.
    # This is Ubuntu 20.04, latest patch. A specific patch version can be specified instead, if desired.
    machine:
      image: ubuntu-2004:current
    # This determines the amount of virtual CPU and RAM the job has. A larger or smaller size might be used, if needed.
    # See: https://circleci.com/docs/2.0/executor-types/#using-machine
    resource_class: medium
    steps:
      - checkout
      - run:
          name: "Say Hello From Machine"
          command: "echo Hello from machine!"

# Invoke jobs via workflows
# See: https://circleci.com/docs/2.0/configuration-reference/#workflows
workflows:
  say-hello-workflow:
    jobs:
      - say-hello-docker
      - say-hello-machine

For further information, see https://circleci.com/docs/2.0/executor-types/#using-docker.