[GitHub] XD-DENG opened a new pull request #3698: [AIRFLOW-2855] Check Cron Expression Validity in DagBag.process_file()

[GitBox <gi...@apache.org>]

XD-DENG opened a new pull request #3698: [AIRFLOW-2855] Check Cron Expression Validity in DagBag.process_file()
URL: https://github.com/apache/incubator-airflow/pull/3698
 
 
   ### Jira
   
   - [x] 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-2855
     - 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
   
   - [x] Here are some details about my PR, including screenshots of any UI changes:
   
   `schedule_interval` of DAGs can either be timedelta or a Cron expression.
   
   When it's a Cron expression, there is no mechanism to check its validity at this moment. If there is anything wrong with the Cron expression itself, it will cause issues when methods `following_schedule()`  and `previous_schedule()` are invoked (will affect scheduling).
   
   However, exceptions will only be written into logs. From Web UI, it’s hard for users to identify this issue & the source while no new task can be initiated (especially for users who’re not very familiar with Cron).
   
    It may be good to show error messages in web UI when a DAG's Cron expression (as schedule_interval) can not be parsed by `croniter` properly (this is implemented by adding these exceptions into metadata `import_error`, whose entries will be shown as error messages in web UI).
   
   Related tests are added as well.
   
   **Screenshot**
   <img width="1680" alt="screen shot 2018-08-05 at 10 23 46 pm" src="https://user-images.githubusercontent.com/11539188/43687000-0ced5a5e-9901-11e8-85ba-b1d8ce0fce9f.png">
   
   
   
   ### Tests
   
   - [ ] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   ### Commits
   
   - [ ] 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
   
   - [ ] 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
   
   - [x] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
   

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
users@infra.apache.org


With regards,
Apache Git Services