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• • LocationId denotes the physical execution environment required to run a stream processor. LocationId is used to uniquely identify a environment amongst all available physical execution environments. ProcessorId is used to uniquely identify a stream processor in a processors group. ProcessorId and localityId are two different, logically orthogonal concepts which cannot be unified.
  • Standalone model supports running multiple stream processors from a single JVM on a physical host. If a stream processor(P1) running a physical host(H) dies, it’s optimal to redistribute the tasks of the dead processor(P1) to the other processors running on the host(H). If processorId is used as localityId, this optimal generation cannot be achieved(since task to localityId association is not maintained).
  • In case of LinkedIn execution environment, locationId will be a composite key comprised of sliceID and sliceInstanceId. In case of kubernetes, locationId will be containerId(which will be obtained through POD API).

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Zookeeper is used in standalone for coordination between the stream processors of a stream application. Amongst all the available processors of a stream application, a single processor will be elected as a leader in standalone. In the standalone deployment model, the JobModel is stored in zookeeper. The leader will generate the JobModel and propagate the JobModel to all the other processors in the group. Distributed barrier in zookeeper will be used to block the message processing until the latest JobModel is picked by all the processors in the group. 

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ZK Data Model to support host affinity:

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