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• Introduce the new interface
• Add unit tests to test/verify compatibility
• JobModel compatibility - The data model hierarchy used "int" as containerId everywhere (as a key in JobModel & as a member variable in ContainerModel). JobModel is read from / written to CoordinatorStream using Jackson based serializer/deserializers. This needs to be changed to handle deserialization of old "int" containerIds, in order to not break existing Yarn jobs. 
• Certain parts of the code implicitly assume the "comparable" nature of ContainerModel that relies on integer comparison of containerId. An example would be the TaskNameGrouper - GroupByContainerCount. In general, the TaskNameGrouper should take in a list of processorId, as opposed to assuming that processorId always falls within the 0 to N-1 range

Compatibility, Deprecation, and Migration Plan

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