[GitHub] [samza] Sanil15 opened a new pull request #1227: SAMZA-2404: Container Placement Handler for dispatching container placement messages between metastore and JobCoordinator

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

Sanil15 opened a new pull request #1227: SAMZA-2404: Container Placement Handler for dispatching container placement messages between metastore and JobCoordinator
URL: https://github.com/apache/samza/pull/1227
 
 
   **Design:** [SEP-22: Container Placements in Samza](https://cwiki.apache.org/confluence/display/SAMZA/SEP-22%3A+Container+Placements+in+Samza)
   
   **Changes:** : Following abilities are added as a part of this PR:
   
   1. Container placement handler which is a stateless handler that periodically dispatches messages between the Metadata store and the Container Placement Service APIs running as a part of Job Coordinator
   2. ContainerPlacementRequestMessage & ContainerPlacementResponseMessage are two POJO used to encapsulate request & response messages for container placement actions
   3. Custom ObjectMapper for serializing and deserializing these messages is added as a part of ContainerPlacementMessageObjectMapper
   
   **Tests:** 
   1. Unit tests are added to test message serialization & deserialization
   2. Unit tests to test ContainerPlacementHandler
   2. Manual testing has been done to see reads / writes from meta-store
   
   **API Changes:**: 
   1. Adds two new public exposed API class: ContainerPlacementRequestMessage & ContainerPlacementResponseMessage in samza-api
   2. ContainerPlacementRequestMessage are messages used to issue container placement actions, one can write these messages to meta-store using Meta-store writer 
   3. ContainerPlacementResponseMessage are messages used as a response to container placement actions, Job Coordinator writes these messages to Meta-store so external controllers can read response to the current actions
   
   **Upgrade Instructions:** Existing jobs with a persisted metastore will be able to ignore these newly populated messages because they have a different namespace
   
   **Usage Instructions:** An external controller / tool (ex: CoordinatorStreamWriter) would be able to issue such actions by writing to metastore (currently: CoordinatorStream) 

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