Minimalistic docker image to cancel CircleCI 2.0 redundant builds

Unfortunately, CircleCI 2.0 workflow doesn't support cancellation of redundant builds as opposed to 1.0 version. When you push your code too often, the whole CI workflow can be stuck unless all your previous jobs are performed.

How it works

• The script inside docker container understands repository, current branch and build number from built-in ENV variables
• Fetches the list of the running or enqueued builds within current branch
• Excludes current build from the list of candidates
• Cancels redundant builds one by one

Installation

Ready docker image is available on Docker Hub.

• Generate CircleCI API using your account dashboard
• Add it as CIRCLE_TOKEN environment variable to your project settings
• Add a separate job using sponomarev/circleci-cancel-builds docker image as a required first step in your build workflow
• Invoke run command

version: 2

workflows:
  version: 2
  build_and_test:
    jobs:
      - cancel_redundant_builds
      - checkout:
          requires:
            - cancel_redundant_builds

jobs:
  cancel_redundant_builds:
    docker:
      - image: sponomarev/circleci-cancel-builds
    steps:
      - run:
          name: Cancelling redundant builds
          command: run

Limitations

Honestly, this solution is not ideal – it requires your workflow to start and cancellation job to be invoked. It can take some time before you get a released container, but still, it's better than nothing. It's a pity that CircleCI API doesn't provide any way to control workflows directly.

Acknowledgments

A big thanks to Luberj from CircleCI forum who provided an idea to cancel builds with API methods.

License

The code is available as open source under the terms of the MIT License.