[GitHub] akirillov commented on issue #22071: [SPARK-25088][CORE][MESOS][DOCS] Update Rest Server docs & defaults.

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akirillov commented on issue #22071: [SPARK-25088][CORE][MESOS][DOCS] Update Rest Server docs & defaults.
URL: https://github.com/apache/spark/pull/22071#issuecomment-465826399
 
 
   Hi @squito, if I may, I have a few comments to share regarding this change and probably you can help me to understand it in better details.
   
   From  [Spark Security Doc page](https://spark.apache.org/docs/latest/security.html#standalone-mode-only) it looks like `spark.master.rest.enabled` property belongs to Spark Standalone Master only. IMO, It makes sense, because it's the server side who is responsible for enabling and disabling REST endpoint according to the [source code](https://github.com/apache/spark/blob/v2.4.0/core/src/main/scala/org/apache/spark/deploy/master/Master.scala#L154-L157).
   
   Now, from the [comment in the code] (https://github.com/apache/spark/blob/v2.4.0/core/src/main/scala/org/apache/spark/deploy/SparkSubmit.scala#L176-L180) of `SparkSubmit.scala` it looks like REST-based gateway introduced in Spark 1.3 is the default way of communication with Spark Standalone Master with a fallback to legacy RPC.
   
   And here's the problem: now `spark.master.rest.enabled` became a client-side property, not Spark Standalone Master property. So in order to communicate with Master, a user have to provide `spark.master.rest.enabled` with each job she submits because without it, the submission will fail. This is a pretty breaking change.
   
   What is the reason to fail the start of [MesosClusterDispatcher](https://github.com/apache/spark/blob/v2.4.0/resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/MesosClusterDispatcher.scala#L54-L60) if `spark.authenticate.secret` is set? Mesos uses different mechanisms for authentication and there's no need to fail the Dispatcher - this property can be just ignored or logged at most.
   
   TL;DR It looks like `spark.master.rest.enabled` should reside only in Spark Standalone Master code and shouldn't leak into the client side of `SparkSubmit`. Also, it can be completely ignored with Mesos Dispatcher, because REST interface is the only endpoint it exposes.
   
   Please let me know what you think. Thanks.

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