[SPARK-10812] [YARN] Spark hadoop util support switching to yarn

While this is likely not a huge issue for real production systems, for test systems which may setup a Spark Context and tear it down and stand up a Spark Context with a different master (e.g. some local mode & some yarn mode) tests this cane be an issue. Discovered during work on spark-testing-base on Spark 1.4.1, but seems like the logic that triggers it is present in master (see SparkHadoopUtil object). A valid work around for users encountering this issue is to fork a different JVM, however this can be heavy weight.

```
[info] SampleMiniClusterTest:
[info] Exception encountered when attempting to run a suite with class name: com.holdenkarau.spark.testing.SampleMiniClusterTest *** ABORTED ***
[info] java.lang.ClassCastException: org.apache.spark.deploy.SparkHadoopUtil cannot be cast to org.apache.spark.deploy.yarn.YarnSparkHadoopUtil
[info] at org.apache.spark.deploy.yarn.YarnSparkHadoopUtil$.get(YarnSparkHadoopUtil.scala:163)
[info] at org.apache.spark.deploy.yarn.Client.prepareLocalResources(Client.scala:257)
[info] at org.apache.spark.deploy.yarn.Client.createContainerLaunchContext(Client.scala:561)
[info] at org.apache.spark.deploy.yarn.Client.submitApplication(Client.scala:115)
[info] at org.apache.spark.scheduler.cluster.YarnClientSchedulerBackend.start(YarnClientSchedulerBackend.scala:57)
[info] at org.apache.spark.scheduler.TaskSchedulerImpl.start(TaskSchedulerImpl.scala:141)
[info] at org.apache.spark.SparkContext.<init>(SparkContext.scala:497)
[info] at com.holdenkarau.spark.testing.SharedMiniCluster$class.setup(SharedMiniCluster.scala:186)
[info] at com.holdenkarau.spark.testing.SampleMiniClusterTest.setup(SampleMiniClusterTest.scala:26)
[info] at com.holdenkarau.spark.testing.SharedMiniCluster$class.beforeAll(SharedMiniCluster.scala:103)
```

Author: Holden Karau <holden@pigscanfly.ca>

Closes #8911 from holdenk/SPARK-10812-spark-hadoop-util-support-switching-to-yarn.

2 files changed, 17 insertions, 1 deletions

diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
index a2c4bc2f54..8c53c24a79 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
@@ -86,7 +86,11 @@ private[spark] class Client(
   private val fireAndForget = isClusterMode &&
     !sparkConf.getBoolean("spark.yarn.submit.waitAppCompletion", true)
 
-  def stop(): Unit = yarnClient.stop()
+  def stop(): Unit = {
+    yarnClient.stop()
+    // Unset YARN mode system env variable, to allow switching between cluster types.
+    System.clearProperty("SPARK_YARN_MODE")
+  }
 
   /**
    * Submit an application running our ApplicationMaster to the ResourceManager.
diff --git a/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnSparkHadoopUtilSuite.scala b/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnSparkHadoopUtilSuite.scala
index 49bee0866d..e1c67db765 100644
--- a/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnSparkHadoopUtilSuite.scala
+++ b/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnSparkHadoopUtilSuite.scala
@@ -30,6 +30,7 @@ import org.scalatest.Matchers
 import org.apache.hadoop.yarn.api.records.ApplicationAccessType
 
 import org.apache.spark.{Logging, SecurityManager, SparkConf, SparkException, SparkFunSuite}
+import org.apache.spark.deploy.SparkHadoopUtil
 import org.apache.spark.util.Utils
 
 
@@ -233,4 +234,15 @@ class YarnSparkHadoopUtilSuite extends SparkFunSuite with Matchers with Logging
       }
     assert(caught.getMessage === "Can't get Master Kerberos principal for use as renewer")
   }
+
+  test("check different hadoop utils based on env variable") {
+    try {
+      System.setProperty("SPARK_YARN_MODE", "true")
+      assert(SparkHadoopUtil.get.getClass === classOf[YarnSparkHadoopUtil])
+      System.setProperty("SPARK_YARN_MODE", "false")
+      assert(SparkHadoopUtil.get.getClass === classOf[SparkHadoopUtil])
+    } finally {
+      System.clearProperty("SPARK_YARN_MODE")
+    }
+  }
 }