[GitHub] [incubator-gobblin] autumnust opened a new pull request #2647: [GOBBLIN-781] Skeleton for GaaS DR mode clean transition

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autumnust opened a new pull request #2647: [GOBBLIN-781] Skeleton for GaaS DR mode clean transition
URL: https://github.com/apache/incubator-gobblin/pull/2647
 
 
   Dear Gobblin maintainers,
   
   Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!
   
   A little bit background on this PR: 
   In Gobblin-as-a-Service deployment, there are extreme cases that the whole data center where a GaaS cluster is deployed went down. In that case we will launch another GaaS cluster to handle request-serving and orchestration. To guarantee a valid working state for DR-Nominated GaaS Cluster, we will need to clean certain left-over states.  Also, not all `FlowSpec`s would be eligible for running in alternative environment due to data affinity or so. So we provide `SpecStore` an ability to tag certain `FlowSpec`s and only those will be picked up by DR-Nominated cluster to work on. 
   
   
   ### JIRA
   - [x] My PR addresses the following [Gobblin JIRA]
       - https://issues.apache.org/jira/browse/GOBBLIN-781
   
   
   ### Description
   - [x] Here are some details about my PR, including screenshots (if applicable):
   
   This PR is mainly solving problems mentioned in background sections by: 
   - Adding "tag" into `MysqlSpecStore`. 
   - Adding `isNominatedDRHanlder ` as a configuration for newly-launched GaaS master node.
   - Adding logic inside `scheduleSpecsFromCatalog`  to pick up tagged `FlowSpec`s in DR-nominated node. This is just a skeleton code for now since the real cancellation features is not yet there. 
   - Fixing some of API in `SpecStore` and deprecated the old method load all `Spec`s into memory. 
   - Some changes in `GobblinServiceManager` to get rid of left-over during prototyping phase.
   
   ### Tests
   - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
      - Unit test for loading `spec`s with tag. 
   
   
   ### 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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