[GitHub] [incubator-gobblin] htran1 opened a new pull request #2644: [GOBBLIN-780] Handle scenarios that cause the YarnAutoScalingManager …

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htran1 opened a new pull request #2644: [GOBBLIN-780] Handle scenarios that cause the YarnAutoScalingManager …
URL: https://github.com/apache/incubator-gobblin/pull/2644
 
 
   …to be stuck
   
   Dear Gobblin maintainers,
   
   Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!
   
   
   ### JIRA
   - [X] My PR addresses the following [Gobblin JIRA](https://issues.apache.org/jira/browse/GOBBLIN/) issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
       - https://issues.apache.org/jira/browse/GOBBLIN-780
   
   
   ### Description
   - [X] Here are some details about my PR, including screenshots (if applicable):
   Issue 1: The YarnAutoScalingRunnable is run in a fixed schedule by a ScheduledExecutorService in YarnAutoScalingManager. If the runnable encounters an exception the the executor service will stop scheduling it. Catch all exceptions in the runnable, log, and do not re-raise.
   
   Issue 2: The auto scaler may reduce the container count to 0. Helix will not schedule any flows if there are no participants connected. This results in the auto scaler keeping the container count at 0 and no progress is made. Fix this by not allowing the container count to be reduced below 1.
   
   ### Tests
   - [X] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   
   ### 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
       2. Subject is limited to 50 characters
       3. Subject does not end with a period
       4. Subject uses the imperative mood ("add", not "adding")
       5. Body wraps at 72 characters
       6. Body explains "what" and "why", not "how"
   
   

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