[SPARK-25262][K8S] Better support configurability of Spark scratch space when using Kubernetes

docs/running-on-kubernetes.md

@@ -215,6 +215,22 @@ spark.kubernetes.driver.volumes.persistentVolumeClaim.checkpointpvc.options.clai
 
 The configuration properties for mounting volumes into the executor pods use prefix `spark.kubernetes.executor.` instead of `spark.kubernetes.driver.`. For a complete list of available options for each supported type of volumes, please refer to the [Spark Properties](#spark-properties) section below. 
 
+## Local Storage
+
+Spark uses temporary scratch space to spill data to disk during shuffles and other operations.  When using Kubernetes as the resource manager the pods will be created with an [emptyDir](https://kubernetes.io/docs/concepts/storage/volumes/#emptydir) volume mounted for each directory listed in `SPARK_LOCAL_DIRS`.  If no directories are explicitly specified then a default directory is created and configured appropriately.
+
+`emptyDir` volumes use the ephemeral storage feature of Kubernetes and do not persist beyond the life of the pod.
+
+### Using RAM for local storage
+
+As `emptyDir` volumes use the nodes backing storage for ephemeral storage this default behaviour may not be appropriate for some compute environments.  For example if you have diskless nodes with remote storage mounted over a network having lots of executors doing IO to this remote storage may actually degrade performance.
+
+In this case it may be desirable to set `spark.kubernetes.local.dirs.tmpfs=true` in your configuration which will cause the `emptyDir` volumes to be configured as `tmpfs` i.e. RAM backed volumes.  When configured like this Sparks local storage usage will count towards your pods memory usage therefore you may wish to increase your memory requests via the normal `spark.driver.memory` and `spark.executor.memory` configuration properties.
+
+### Using arbitrary volumes for local storage
+
+Alternatively if using the pod template feature you can provide a volume named `spark-local-dirs-N`, where N is a 1 based index to the entires in your `SPARK_LOCAL_DIRS` variable, in your specification and that will be used for local storage.  This enables you to use a volume type that is appropriate to your compute environment.
+
 ## Introspection and Debugging
 
 These are the different ways in which you can investigate a running/completed Spark application, monitor progress, and

resource-managers/kubernetes/core/src/main/scala/org/apache/spark/deploy/k8s/Config.scala

@@ -225,6 +225,15 @@ private[spark] object Config extends Logging {
         "Ensure that major Python version is either Python2 or Python3")
       .createWithDefault("2")
 
+  val KUBERNETES_LOCAL_DIRS_TMPFS =
+    ConfigBuilder("spark.kubernetes.local.dirs.tmpfs")
+      .doc("If set to true then emptyDir volumes created to back spark.local.dirs will have " +
+        "their medium set to Memory so that they will be created as tmpfs (i.e. RAM) backed " +
+        "volumes. This may improve performance but scratch space usage will count towards " +
+        "your pods memory limit so you may wish to request more memory.")
+    .booleanConf
+    .createWithDefault(false)
+
   val KUBERNETES_AUTH_SUBMISSION_CONF_PREFIX =
     "spark.kubernetes.authenticate.submission"
 

resource-managers/kubernetes/core/src/main/scala/org/apache/spark/deploy/k8s/features/LocalDirsFeatureStep.scala

@@ -19,9 +19,12 @@ package org.apache.spark.deploy.k8s.features
 import java.nio.file.Paths
 import java.util.UUID
 
-import io.fabric8.kubernetes.api.model.{ContainerBuilder, HasMetadata, PodBuilder, VolumeBuilder, VolumeMountBuilder}
+import collection.JavaConverters._
+import io.fabric8.kubernetes.api.model.{ContainerBuilder, HasMetadata, PodBuilder, VolumeBuilder, VolumeMount, VolumeMountBuilder}
 
+import org.apache.spark.SparkException
 import org.apache.spark.deploy.k8s.{KubernetesConf, KubernetesDriverSpecificConf, KubernetesRoleSpecificConf, SparkPod}
+import org.apache.spark.deploy.k8s.Config._
 
 private[spark] class LocalDirsFeatureStep(
     conf: KubernetesConf[_ <: KubernetesRoleSpecificConf],
@@ -37,41 +40,99 @@ private[spark] class LocalDirsFeatureStep(
     .orElse(conf.getOption("spark.local.dir"))
     .getOrElse(defaultLocalDir)
     .split(",")
+  private val useLocalDirTmpFs = conf.get(KUBERNETES_LOCAL_DIRS_TMPFS)
 
   override def configurePod(pod: SparkPod): SparkPod = {
     val localDirVolumes = resolvedLocalDirs
       .zipWithIndex
       .map { case (localDir, index) =>
-        new VolumeBuilder()
-          .withName(s"spark-local-dir-${index + 1}")
-          .withNewEmptyDir()
-          .endEmptyDir()
-          .build()
+        val name = s"spark-local-dir-${index + 1}"
+        // To allow customisation of local dirs backing volumes we should avoid creating
+        // emptyDir volumes if the volume is already defined in the pod spec
+        hasVolume(pod, name) match {
+          case true =>
+            // For pre-existing volume definitions just re-use the volume
+            pod.pod.getSpec().getVolumes().asScala.find(v => v.getName.equals(name)).get
+          case false =>
+            // Create new emptyDir volume
+            new VolumeBuilder()
+              .withName(name)
+              .withNewEmptyDir()
+                .withMedium(useLocalDirTmpFs match {
+                  case true => "Memory" // Use tmpfs
+                  case false => null    // Default - use nodes backing storage
+                })
+              .endEmptyDir()
+              .build()
+        }
       }
+
     val localDirVolumeMounts = localDirVolumes
       .zip(resolvedLocalDirs)
       .map { case (localDirVolume, localDirPath) =>
-        new VolumeMountBuilder()
-          .withName(localDirVolume.getName)
-          .withMountPath(localDirPath)
-          .build()
+        hasVolumeMount(pod, localDirVolume.getName, localDirPath) match {
+          case true =>
+            // For pre-existing volume mounts just re-use the mount
+            pod.container.getVolumeMounts().asScala
+              .find(m => m.getName.equals(localDirVolume.getName)
+                         && m.getMountPath.equals(localDirPath))
+              .get
+          case false =>
+            // Create new volume mount
+            new VolumeMountBuilder()
+              .withName (localDirVolume.getName)
+              .withMountPath (localDirPath)
+              .build()
+        }
+      }
+
+    // Check for conflicting volume mounts
+    for (m: VolumeMount <- localDirVolumeMounts) {
+      if (hasConflictingVolumeMount(pod, m.getName, m.getMountPath).size > 0) {
+        throw new SparkException(s"Conflicting volume mounts defined, pod template attempted to " +
+          "mount SPARK_LOCAL_DIRS volume ${m.getName} multiple times or at an alternative path " +
+          "then the expected ${m.getPath}")
       }
+    }
+
     val podWithLocalDirVolumes = new PodBuilder(pod.pod)
       .editSpec()
-        .addToVolumes(localDirVolumes: _*)
+         // Don't want to re-add volumes that already existed in the incoming spec
+         // as duplicate definitions will lead to K8S API errors
+        .addToVolumes(localDirVolumes.filter(v => !hasVolume(pod, v.getName)): _*)
         .endSpec()
       .build()
     val containerWithLocalDirVolumeMounts = new ContainerBuilder(pod.container)
       .addNewEnv()
         .withName("SPARK_LOCAL_DIRS")
         .withValue(resolvedLocalDirs.mkString(","))
         .endEnv()
-      .addToVolumeMounts(localDirVolumeMounts: _*)
+      // Don't want to re-add volume mounts that already existed in the incoming spec
+      // as duplicate definitions will lead to K8S API errors
+      .addToVolumeMounts(localDirVolumeMounts
+                         .filter(m => !hasVolumeMount(pod, m.getName, m.getMountPath)): _*)
       .build()
     SparkPod(podWithLocalDirVolumes, containerWithLocalDirVolumeMounts)
   }
 
   override def getAdditionalPodSystemProperties(): Map[String, String] = Map.empty
 
   override def getAdditionalKubernetesResources(): Seq[HasMetadata] = Seq.empty
+
+  def hasVolume(pod: SparkPod, name: String): Boolean = {
+    pod.pod.getSpec().getVolumes().asScala.exists(v => v.getName.equals(name))
+  }
+
+  def hasVolumeMount(pod: SparkPod, name: String, path: String): Boolean = {
+    pod.container.getVolumeMounts().asScala
+      .exists(m => m.getName.equals(name) && m.getMountPath.equals(path))
+  }
+
+  def hasConflictingVolumeMount(pod: SparkPod, name: String, path: String): Seq[VolumeMount] = {
+    // A volume mount is considered conflicting if it matches one, and only one of, the name/path
+    // of a volume mount we are creating
+    pod.container.getVolumeMounts().asScala
+      .filter(m => (m.getName.equals(name) && !m.getMountPath.equals(path)) ||
+                   (m.getMountPath.equals(path) && !m.getName.equals(name)))
+  }
 }

resource-managers/kubernetes/core/src/test/scala/org/apache/spark/deploy/k8s/features/LocalDirsFeatureStepSuite.scala

@@ -16,12 +16,15 @@
  */
 package org.apache.spark.deploy.k8s.features
 
-import io.fabric8.kubernetes.api.model.{EnvVarBuilder, VolumeBuilder, VolumeMountBuilder}
+import io.fabric8.kubernetes.api.model.{ContainerBuilder, EnvVarBuilder, PodBuilder, VolumeBuilder, VolumeMountBuilder}
 import org.mockito.Mockito
+import org.scalatest._
+import Matchers._
 import org.scalatest.BeforeAndAfter
 
-import org.apache.spark.{SparkConf, SparkFunSuite}
+import org.apache.spark.{SparkConf, SparkException, SparkFunSuite}
 import org.apache.spark.deploy.k8s.{KubernetesConf, KubernetesDriverSpecificConf, KubernetesRoleSpecificConf, SparkPod}
+import org.apache.spark.deploy.k8s.Config._
 
 class LocalDirsFeatureStepSuite extends SparkFunSuite with BeforeAndAfter {
   private val defaultLocalDir = "/var/data/default-local-dir"
@@ -111,4 +114,146 @@ class LocalDirsFeatureStepSuite extends SparkFunSuite with BeforeAndAfter {
         .withValue("/var/data/my-local-dir-1,/var/data/my-local-dir-2")
         .build())
   }
+
+  test("Use predefined volume for local dirs") {
+    Mockito.doReturn(null).when(sparkConf).get("spark.local.dir")
+    Mockito.doReturn(null).when(sparkConf).getenv("SPARK_LOCAL_DIRS")
+    val stepUnderTest = new LocalDirsFeatureStep(kubernetesConf, defaultLocalDir)
+    val initialPod =
+      new PodBuilder(SparkPod.initialPod().pod)
+        .editSpec()
+          .addToVolumes(new VolumeBuilder()
+            .withName("spark-local-dir-1")
+            .withNewConfigMap()
+              .withName("foo")
+            .endConfigMap()
+            .build())
+        .endSpec()
+      .build()
+
+    val configuredPod = stepUnderTest.configurePod(new SparkPod(initialPod,
+      new ContainerBuilder().build()))
+    assert(configuredPod.pod.getSpec.getVolumes.size === 1)
+    assert(configuredPod.pod.getSpec.getVolumes.get(0) ===
+      new VolumeBuilder()
+        .withName(s"spark-local-dir-1")
+        .withNewConfigMap()
+          .withName("foo")
+        .endConfigMap()
+        .build())
+    assert(configuredPod.container.getVolumeMounts.size === 1)
+    assert(configuredPod.container.getVolumeMounts.get(0) ===
+      new VolumeMountBuilder()
+        .withName(s"spark-local-dir-1")
+        .withMountPath(defaultLocalDir)
+        .build())
+    assert(configuredPod.container.getEnv.size === 1)
+    assert(configuredPod.container.getEnv.get(0) ===
+      new EnvVarBuilder()
+        .withName("SPARK_LOCAL_DIRS")
+        .withValue(defaultLocalDir)
+        .build())
+  }
+
+  test("Use predefined volume and mount for local dirs") {
+    Mockito.doReturn(null).when(sparkConf).get("spark.local.dir")
+    Mockito.doReturn(null).when(sparkConf).getenv("SPARK_LOCAL_DIRS")
+    val stepUnderTest = new LocalDirsFeatureStep(kubernetesConf, defaultLocalDir)
+    val initialPod =
+      new PodBuilder(SparkPod.initialPod().pod)
+        .editSpec()
+        .addToVolumes(new VolumeBuilder()
+          .withName("spark-local-dir-1")
+          .withNewConfigMap()
+          .withName("foo")
+          .endConfigMap()
+          .build())
+        .endSpec()
+        .build()
+    val initialContainer =
+      new ContainerBuilder()
+        .withVolumeMounts(new VolumeMountBuilder()
+          .withName("spark-local-dir-1")
+          .withMountPath(defaultLocalDir)
+          .build())
+        .build()
+
+    val configuredPod = stepUnderTest.configurePod(new SparkPod(initialPod,
+      initialContainer))
+    assert(configuredPod.pod.getSpec.getVolumes.size === 1)
+    assert(configuredPod.pod.getSpec.getVolumes.get(0) ===
+      new VolumeBuilder()
+        .withName(s"spark-local-dir-1")
+        .withNewConfigMap()
+        .withName("foo")
+        .endConfigMap()
+        .build())
+    assert(configuredPod.container.getVolumeMounts.size === 1)
+    assert(configuredPod.container.getVolumeMounts.get(0) ===
+      new VolumeMountBuilder()
+        .withName(s"spark-local-dir-1")
+        .withMountPath(defaultLocalDir)
+        .build())
+    assert(configuredPod.container.getEnv.size === 1)
+    assert(configuredPod.container.getEnv.get(0) ===
+      new EnvVarBuilder()
+        .withName("SPARK_LOCAL_DIRS")
+        .withValue(defaultLocalDir)
+        .build())
+  }
+
+  test("Using conflicting volume mount for local dirs should error") {
+    Mockito.doReturn(null).when(sparkConf).get("spark.local.dir")
+    Mockito.doReturn(null).when(sparkConf).getenv("SPARK_LOCAL_DIRS")
+    val stepUnderTest = new LocalDirsFeatureStep(kubernetesConf, defaultLocalDir)
+    val initialPod =
+      new PodBuilder(SparkPod.initialPod().pod)
+        .editSpec()
+        .addToVolumes(new VolumeBuilder()
+          .withName("spark-local-dir-1")
+          .withNewConfigMap()
+          .withName("foo")
+          .endConfigMap()
+          .build())
+        .endSpec()
+        .build()
+    val initialContainer =
+      new ContainerBuilder()
+        .withVolumeMounts(new VolumeMountBuilder()
+          .withName("spark-local-dir-1")
+          .withMountPath("/bad/path")
+          .build())
+        .build()
+
+    an [SparkException] should be thrownBy stepUnderTest.configurePod(new SparkPod(initialPod,
+      initialContainer))
+  }
+
+  test("Use tmpfs to back default local dir") {
+    Mockito.doReturn(null).when(sparkConf).get("spark.local.dir")
+    Mockito.doReturn(null).when(sparkConf).getenv("SPARK_LOCAL_DIRS")
+    Mockito.doReturn(true).when(sparkConf).get(KUBERNETES_LOCAL_DIRS_TMPFS)
+    val stepUnderTest = new LocalDirsFeatureStep(kubernetesConf, defaultLocalDir)
+    val configuredPod = stepUnderTest.configurePod(SparkPod.initialPod())
+    assert(configuredPod.pod.getSpec.getVolumes.size === 1)
+    assert(configuredPod.pod.getSpec.getVolumes.get(0) ===
+      new VolumeBuilder()
+        .withName(s"spark-local-dir-1")
+        .withNewEmptyDir()
+          .withMedium("Memory")
+        .endEmptyDir()
+        .build())
+    assert(configuredPod.container.getVolumeMounts.size === 1)
+    assert(configuredPod.container.getVolumeMounts.get(0) ===
+      new VolumeMountBuilder()
+        .withName(s"spark-local-dir-1")
+        .withMountPath(defaultLocalDir)
+        .build())
+    assert(configuredPod.container.getEnv.size === 1)
+    assert(configuredPod.container.getEnv.get(0) ===
+      new EnvVarBuilder()
+        .withName("SPARK_LOCAL_DIRS")
+        .withValue(defaultLocalDir)
+        .build())
+  }
 }