[GitHub] [pulsar-helm-chart] michaeljmarshall commented on pull request #127: Antiaffinity with zone topology for high availability

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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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