[SPARK-6331] Load new master URL if present when recovering streaming context from checkpoint

In streaming driver recovery, when the SparkConf is reconstructed based on the checkpointed configuration, it recovers the old master URL. This okay if the cluster on which the streaming application is relaunched is the same cluster as it was running before. But if that cluster changes, there is no way to inject the new master URL of the new cluster. As a result, the restarted app tries to connect to the non-existent old cluster and fails.

The solution is to check whether a master URL is set in the System properties (by Spark submit) before recreating the SparkConf. If a new master url is set in the properties, then use it as that is obviously the most relevant one. Otherwise load the old one (to maintain existing behavior).

Author: Tathagata Das <[email protected]>

Closes #5024 from tdas/SPARK-6331 and squashes the following commits:

392fd44 [Tathagata Das] Fixed naming issue.
c7c0b99 [Tathagata Das] Addressed comments.
6a0857c [Tathagata Das] Updated testsuites.
222485d [Tathagata Das] Load new master URL if present when recovering streaming context from checkpoint

(cherry picked from commit c928796)
Signed-off-by: Tathagata Das <[email protected]>

Author: tdas

streaming/src/main/scala/org/apache/spark/streaming/Checkpoint.scala

@@ -43,10 +43,13 @@ class Checkpoint(@transient ssc: StreamingContext, val checkpointTime: Time)
   val delaySeconds = MetadataCleaner.getDelaySeconds(ssc.conf)
   val sparkConfPairs = ssc.conf.getAll
 
-  def sparkConf = {
-    new SparkConf(false).setAll(sparkConfPairs)
+  def createSparkConf(): SparkConf = {
+    val newSparkConf = new SparkConf(loadDefaults = false).setAll(sparkConfPairs)
       .remove("spark.driver.host")
       .remove("spark.driver.port")
+    val newMasterOption = new SparkConf(loadDefaults = true).getOption("spark.master")
+    newMasterOption.foreach { newMaster => newSparkConf.setMaster(newMaster) }
+    newSparkConf
   }
 
   def validate() {

streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala

@@ -116,7 +116,7 @@ class StreamingContext private[streaming] (
 
   private[streaming] val sc: SparkContext = {
     if (isCheckpointPresent) {
-      new SparkContext(cp_.sparkConf)
+      new SparkContext(cp_.createSparkConf())
     } else {
       sc_
     }

streaming/src/test/scala/org/apache/spark/streaming/CheckpointSuite.scala

@@ -146,15 +146,15 @@ class CheckpointSuite extends TestSuiteBase {
 
   // This tests whether spark conf persists through checkpoints, and certain
   // configs gets scrubbed
-  test("persistence of conf through checkpoints") {
+  test("recovery of conf through checkpoints") {
     val key = "spark.mykey"
     val value = "myvalue"
     System.setProperty(key, value)
     ssc = new StreamingContext(master, framework, batchDuration)
     val originalConf = ssc.conf
 
     val cp = new Checkpoint(ssc, Time(1000))
-    val cpConf = cp.sparkConf
+    val cpConf = cp.createSparkConf()
     assert(cpConf.get("spark.master") === originalConf.get("spark.master"))
     assert(cpConf.get("spark.app.name") === originalConf.get("spark.app.name"))
     assert(cpConf.get(key) === value)
@@ -163,7 +163,8 @@ class CheckpointSuite extends TestSuiteBase {
     // Serialize/deserialize to simulate write to storage and reading it back
     val newCp = Utils.deserialize[Checkpoint](Utils.serialize(cp))
 
-    val newCpConf = newCp.sparkConf
+    // Verify new SparkConf has all the previous properties
+    val newCpConf = newCp.createSparkConf()
     assert(newCpConf.get("spark.master") === originalConf.get("spark.master"))
     assert(newCpConf.get("spark.app.name") === originalConf.get("spark.app.name"))
     assert(newCpConf.get(key) === value)
@@ -174,6 +175,20 @@ class CheckpointSuite extends TestSuiteBase {
     ssc = new StreamingContext(null, newCp, null)
     val restoredConf = ssc.conf
     assert(restoredConf.get(key) === value)
+    ssc.stop()
+
+    // Verify new SparkConf picks up new master url if it is set in the properties. See SPARK-6331.
+    try {
+      val newMaster = "local[100]"
+      System.setProperty("spark.master", newMaster)
+      val newCpConf = newCp.createSparkConf()
+      assert(newCpConf.get("spark.master") === newMaster)
+      assert(newCpConf.get("spark.app.name") === originalConf.get("spark.app.name"))
+      ssc = new StreamingContext(null, newCp, null)
+      assert(ssc.sparkContext.master === newMaster)
+    } finally {
+      System.clearProperty("spark.master")
+    }
   }
 
 

streaming/src/test/scala/org/apache/spark/streaming/StreamingContextSuite.scala

@@ -100,7 +100,7 @@ class StreamingContextSuite extends FunSuite with BeforeAndAfter with Timeouts w
     assert(cp.sparkConfPairs.toMap.getOrElse("spark.cleaner.ttl", "-1") === "10")
     ssc1.stop()
     val newCp = Utils.deserialize[Checkpoint](Utils.serialize(cp))
-    assert(newCp.sparkConf.getInt("spark.cleaner.ttl", -1) === 10)
+    assert(newCp.createSparkConf().getInt("spark.cleaner.ttl", -1) === 10)
     ssc = new StreamingContext(null, newCp, null)
     assert(ssc.conf.getInt("spark.cleaner.ttl", -1) === 10)
   }