michaeljmarshall commented on pull request #127:
URL: 
https://github.com/apache/pulsar-helm-chart/pull/127#issuecomment-1017883950


   > @sdwerwed: I think the zone affinity would work for stateless components. 
I don't think it will work well for stateful components. Because the location 
of bookie and zookeeper pods will be bound to the location of EBS volumes.
   
   To add some AWS context, EBS volumes are restricted to a single availability 
zone within a region. Once a bookie gets an EBS volume, it cannot be migrated 
to another AZ. I haven't looked closely at this PR, but we'll need to make sure 
that it works for upgrading existing clusters that do not comply with the 
anti-affinity policy.
   
   > Also, even you are able to place bookies across different zones. But you 
don't configure the rack information, so bookkeeper can potentially place two 
same copies in the pods running in the same zone. 
   
   I agree that this could be misleading. We could mitigate the shortcoming 
with documentation, though. Also, this feature can work without configuring 
rack awareness. For example, if your ack quorum is greater than the number of 
bookies in a single AZ, you'll know that your writes are spread across multiple 
AZs and are therefore HA. This isn't as good as configuring rack awareness, but 
it is probably better than random bookie scheduling.


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