[GitHub] [incubator-gobblin] htran1 opened a new pull request #2626: [GOBBLIN-762] Add automatic scaling for Gobblin on YARN

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htran1 opened a new pull request #2626: [GOBBLIN-762] Add automatic scaling for Gobblin on YARN
URL: https://github.com/apache/incubator-gobblin/pull/2626
 
 
   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-762
   
   
   ### Description
   - [X] Here are some details about my PR, including screenshots (if applicable):
   Added `YarnAutoScalingManager` which can be started by the `GobblinApplicationMaster` by setting the `gobblin.yarn.app.master.serviceClasses` configuration. This class runs a scheduled task with a default interval of 60 seconds to detect the number of required partitions for the workflows submitted to Helix. It will request the `YarnService` to scale to a computed number of containers. If the requested number of containers is higher than the YarnService has previously requested then it will request more containers. If the requested count is less than the current number of allocated containers then it will free any unused containers.
   
   ### Tests
   - [X] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   YarnAutoScalingManagerTest and YarnServiceTest
   
   ### 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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