sijie commented on issue #3119: [Feature request] Make brokers read on closest 
Bookie
URL: https://github.com/apache/pulsar/issues/3119#issuecomment-444291637
 
 
   @cbornet : 
   
   > And it shouldn't be hard to expose. I'll try it and propose a PR if it 
works.
   
   that would be great!
   
   > how does the bookkeeper client identify which is its preferred rack ?
   
   from bookkeeper client perspective, the ensemble placement policy will use 
some sort of DNS resolver to resolve a bookie into its network location. the 
network locations will form a network topology of bookies. it will then use 
that the compute the shortest network path to find the best bookie to contract 
to.
   
   in the context of pulsar broker, pulsar provides a REST api for people to 
update the racks for bookies.
   
   > Also it seems the broker BK client has support for 
RackawareEnsemblePlacementPolicy but not for 
RegionAwareEnsemblePlacementPolicy. Wouldn't that be an issue ?
   
   technically you don't have the issue. the existence of 
RegionAwareEnsemblePlacementPolicy is for the case that you need both 
region-aware and within a region you also need rack-aware. in a simpler form to 
think about this is following:
   
   - Rack-Aware is good enough if your network topology only has one level 
(rack or availability zones)
   - Region-Aware is better if your network topology has multiple levels (e.g. 
/region/rack).
   
   In this way, Rackware is good enough for AWS AZs :)

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