[SPARK-25088][CORE][MESOS][DOCS] Update Rest Server docs & defaults.

## What changes were proposed in this pull request?

(a) disabled rest submission server by default in standalone mode
(b) fails the standalone master if rest server enabled & authentication secret set
(c) fails the mesos cluster dispatcher if authentication secret set
(d) doc updates
(e) when submitting a standalone app, only try the rest submission first if spark.master.rest.enabled=true

otherwise you'd see a 10 second pause like
18/08/09 08:13:22 INFO RestSubmissionClient: Submitting a request to launch an application in spark://...
18/08/09 08:13:33 WARN RestSubmissionClient: Unable to connect to server spark://...

I also made sure the mesos cluster dispatcher failed with the secret enabled, though I had to do that on slightly different code as I don't have mesos native libs around.

## How was this patch tested?

I ran the tests in the mesos module & in core for org.apache.spark.deploy.*

I ran a test on a cluster with standalone master to make sure I could still start with the right configs, and would fail the right way too.

Closes #22071 from squito/rest_doc_updates.

Authored-by: Imran Rashid <irashid@cloudera.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>

core/src/main/scala/org/apache/spark/deploy/SparkSubmitArguments.scala

@@ -82,7 +82,7 @@ private[deploy] class SparkSubmitArguments(args: Seq[String], env: Map[String, S
   var driverCores: String = null
   var submissionToKill: String = null
   var submissionToRequestStatusFor: String = null
-  var useRest: Boolean = true // used internally
+  var useRest: Boolean = false // used internally
 
   /** Default properties present in the currently defined defaults file. */
   lazy val defaultSparkProperties: HashMap[String, String] = {
@@ -115,6 +115,8 @@ private[deploy] class SparkSubmitArguments(args: Seq[String], env: Map[String, S
   // Use `sparkProperties` map along with env vars to fill in any missing parameters
   loadEnvironmentArguments()
 
+  useRest = sparkProperties.getOrElse("spark.master.rest.enabled", "false").toBoolean
+
   validateArguments()
 
   /**

core/src/main/scala/org/apache/spark/deploy/master/Master.scala

@@ -121,10 +121,18 @@ private[deploy] class Master(
   }
 
   // Alternative application submission gateway that is stable across Spark versions
-  private val restServerEnabled = conf.getBoolean("spark.master.rest.enabled", true)
+  private val restServerEnabled = conf.getBoolean("spark.master.rest.enabled", false)
   private var restServer: Option[StandaloneRestServer] = None
   private var restServerBoundPort: Option[Int] = None
 
+  {
+    val authKey = SecurityManager.SPARK_AUTH_SECRET_CONF
+    require(conf.getOption(authKey).isEmpty || !restServerEnabled,
+      s"The RestSubmissionServer does not support authentication via ${authKey}.  Either turn " +
+        "off the RestSubmissionServer with spark.master.rest.enabled=false, or do not use " +
+        "authentication.")
+  }
+
   override def onStart(): Unit = {
     logInfo("Starting Spark master at " + masterUrl)
     logInfo(s"Running Spark version ${org.apache.spark.SPARK_VERSION}")

core/src/main/scala/org/apache/spark/deploy/rest/RestSubmissionServer.scala

@@ -51,6 +51,7 @@ private[spark] abstract class RestSubmissionServer(
     val host: String,
     val requestedPort: Int,
     val masterConf: SparkConf) extends Logging {
+
   protected val submitRequestServlet: SubmitRequestServlet
   protected val killRequestServlet: KillRequestServlet
   protected val statusRequestServlet: StatusRequestServlet

docs/running-on-mesos.md

@@ -174,6 +174,8 @@ can find the results of the driver from the Mesos Web UI.
 
 To use cluster mode, you must start the `MesosClusterDispatcher` in your cluster via the `sbin/start-mesos-dispatcher.sh` script,
 passing in the Mesos master URL (e.g: mesos://host:5050). This starts the `MesosClusterDispatcher` as a daemon running on the host.
+Note that the `MesosClusterDispatcher` does not support authentication.  You should ensure that all network access to it is
+protected (port 7077 by default).
 
 By setting the Mesos proxy config property (requires mesos version >= 1.4), `--conf spark.mesos.proxy.baseURL=http://localhost:5050` when launching the dispatcher, the mesos sandbox URI for each driver is added to the mesos dispatcher UI.
 

docs/security.md

@@ -22,7 +22,12 @@ secrets to be secure.
 
 For other resource managers, `spark.authenticate.secret` must be configured on each of the nodes.
 This secret will be shared by all the daemons and applications, so this deployment configuration is
-not as secure as the above, especially when considering multi-tenant clusters.
+not as secure as the above, especially when considering multi-tenant clusters.  In this
+configuration, a user with the secret can effectively impersonate any other user.
+
+The Rest Submission Server and the MesosClusterDispatcher do not support authentication.  You should
+ensure that all network access to the REST API & MesosClusterDispatcher (port 6066 and 7077
+respectively by default) are restricted to hosts that are trusted to submit jobs.
 
 <table class="table">
 <tr><th>Property Name</th><th>Default</th><th>Meaning</th></tr>

resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/MesosClusterDispatcher.scala

@@ -51,6 +51,14 @@ private[mesos] class MesosClusterDispatcher(
     conf: SparkConf)
   extends Logging {
 
+  {
+    // This doesn't support authentication because the RestSubmissionServer doesn't support it.
+    val authKey = SecurityManager.SPARK_AUTH_SECRET_CONF
+    require(conf.getOption(authKey).isEmpty,
+      s"The MesosClusterDispatcher does not support authentication via ${authKey}.  It is not " +
+        s"currently possible to run jobs in cluster mode with authentication on.")
+  }
+
   private val publicAddress = Option(conf.getenv("SPARK_PUBLIC_DNS")).getOrElse(args.host)
   private val recoveryMode = conf.get(RECOVERY_MODE).toUpperCase()
   logInfo("Recovery mode in Mesos dispatcher set to: " + recoveryMode)