Make sure you have checked _all_ steps below. ### Jira
- [ ] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR" - https://issues.apache.org/jira/browse/AIRFLOW-XXX - In case you are fixing a typo in the documentation you can prepend your commit with \[AIRFLOW-XXX\], code changes always need a Jira issue. ### Description In GCP, it is possible to set up [Single node clusters](https://cloud.google.com/dataproc/docs/concepts/configuring-clusters/single-node-clusters) Since the minimal size of the cluster (without this modification) is 3 (one master + two workers). It may be very helpful while doing, for example, small-scale non-critical data processing or building proof-of-concept. ### Tests - [x] My PR adds the following unit tests `test_build_single_node_cluster` and `test_init_with_single_node_and_non_zero_workers` ### Commits - [x] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)": 1. Subject is separated from body by a blank line 1. Subject is limited to 50 characters (not including Jira issue reference) 1. Subject does not end with a period 1. Subject uses the imperative mood ("add", not "adding") 1. Body wraps at 72 characters 1. Body explains "what" and "why", not "how" ### Documentation - [x] In case of new functionality, my PR adds documentation that describes how to use it. - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added. ### Code Quality - [ ] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff` [ Full content available at: https://github.com/apache/incubator-airflow/pull/4015 ] This message was relayed via gitbox.apache.org for devnull@infra.apache.org
