[GitHub] [hadoop] elek opened a new pull request #945: HDDS-1646. Support real persistence in the k8s example files

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elek opened a new pull request #945: HDDS-1646. Support real persistence in the k8s example files 
URL: https://github.com/apache/hadoop/pull/945
 
 
   Ozone release contains example k8s deployment files to make it easier to deploy Ozone to kubernetes. As of now we use emptyDir everywhere, we should support the configuration of host volumes (hostPath or Local Persistent volumes).
   
   The big question here is the default:
   
   * Make the examples easy to start and ephemeral
   * Make the examples more safe, by default (but couldn't be started without additional administration).
   
   (Note this conversation is started in the review of HDDS-1508)
   
   Xiaoyu:  Can we support mount hostVolume for datanode daemons?
   
   Marton: Yes, we can.
   
   AFAIK there are two options:
    * using [hostPath](https://kubernetes.io/docs/concepts/storage/volumes/#hostpath)
    * or with [Local PersistentVolumes](https://kubernetes.io/blog/2018/04/13/local-persistent-volumes-beta/)
   
   The first one requires the knowledge of directory names on the host.
   The second one is recommended but it requires the creation of PersistentVolumes or install a PersistentVolume provider
   
   I am not sure what is the best approach, my current proposal is:
   
    * Use empty dir everywhere to make it easier to start simple ozone cluster
    * Provide simple option to turn on any of theses persistence (the kubernetes files are generated and the generation can be parametrized)
    * Document how to customize the kubernetes resources files
   
   Summary: it's question of the defaults:
    
     1. Use a complex, but persistent solution, which may not work out of the box   
     2. Use a simple, but ephemeral solution (as default)
   
   I started to use (2) but I am open to change.
   
   
   
   See: https://issues.apache.org/jira/browse/HDDS-1646

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