[SPARK-23529][K8s] Support mounting hostPath volumes for executors

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

@@ -117,6 +117,13 @@ private[spark] object Config extends Logging {
       .stringConf
       .createWithDefault("spark")
 
+  val KUBERNETES_EXECUTOR_VOLUMES =
+    ConfigBuilder("spark.kubernetes.executor.volumes")
+      .doc("List of volumes mounted into the executor container. The format of this property is " +
+        "a comma-separated list of mappings following the form hostPath:containerPath[:ro|rw]")
+      .stringConf
+      .createWithDefault("")
+
   val KUBERNETES_ALLOCATION_BATCH_SIZE =
     ConfigBuilder("spark.kubernetes.allocation.batch.size")
       .doc("Number of pods to launch at once in each round of executor allocation.")

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

@@ -16,7 +16,7 @@
  */
 package org.apache.spark.deploy.k8s
 
-import io.fabric8.kubernetes.api.model.LocalObjectReference
+import io.fabric8.kubernetes.api.model._
 
 import org.apache.spark.SparkConf
 import org.apache.spark.util.Utils
@@ -38,7 +38,58 @@ private[spark] object KubernetesUtils {
   }
 
   /**
-   * Parses comma-separated list of imagePullSecrets into K8s-understandable format
+   * Parse a comma-delimited list of volume specs, each of which takes the form
+   * hostPath:containerPath[:ro|rw]; and add volume to pod and volume mount to container.
+   *
+   * @param pod original specification of the pod
+   * @param container original specification of the container
+   * @param volumes list of volume specs
+   * @return a tuple of (pod with the volume(s) added, container with mount(s) added)
+   */
+  def addVolumes(pod: Pod, container : Container, volumes: String): (Pod, Container) = {
+    val podBuilder = new PodBuilder(pod).editOrNewSpec()
+    val containerBuilder = new ContainerBuilder(container)
+    var volumeCount = 0
+    volumes.split(",").map(_.split(":")).map { spec =>
+      var hostPath: Option[String] = None
+      var containerPath: Option[String] = None
+      var readOnly: Option[Boolean] = None
+      spec match {
+        case Array(hostPathV, containerPathV) =>
+          hostPath = Some(hostPathV)
+          containerPath = Some(containerPathV)
+        case Array(hostPathV, containerPathV, "ro") =>
+          hostPath = Some(hostPathV)
+          containerPath = Some(containerPathV)
+          readOnly = Some(true)
+        case Array(hostPathV, containerPathV, "rw") =>
+          hostPath = Some(hostPathV)
+          containerPath = Some(containerPathV)
+          readOnly = Some(false)
+        case spec =>
+          None
+      }
+      if (hostPath.isDefined && containerPath.isDefined) {
+        podBuilder.addToVolumes(new VolumeBuilder()
+            .withHostPath(new HostPathVolumeSource(hostPath.get))
+            .withName(s"hostPath-volume-$volumeCount")
+            .build())
+        val volumeBuilder = new VolumeMountBuilder()
+          .withMountPath(containerPath.get)
+          .withName(s"hostPath-volume-$volumeCount")
+        if (readOnly.isDefined) {
+          containerBuilder.addToVolumeMounts(volumeBuilder.withReadOnly(readOnly.get).build())
+        } else {
+          containerBuilder.addToVolumeMounts(volumeBuilder.build())
+        }
+        volumeCount += 1
+      }
+    }
+    (podBuilder.endSpec().build(), containerBuilder.build())
+  }
+
+  /**
+    * Parses comma-separated list of imagePullSecrets into K8s-understandable format
    */
   def parseImagePullSecrets(imagePullSecrets: Option[String]): List[LocalObjectReference] = {
     imagePullSecrets match {

resource-managers/kubernetes/core/src/main/scala/org/apache/spark/scheduler/cluster/k8s/ExecutorPodFactory.scala

@@ -201,21 +201,27 @@ private[spark] class ExecutorPodFactory(
         .endSpec()
       .build()
 
+    val (executorPodWithVolumes, executorContainerWithVolumes) =
+      KubernetesUtils.addVolumes(executorPod,
+        executorContainer,
+        sparkConf.get(KUBERNETES_EXECUTOR_VOLUMES))
+
     val containerWithLimitCores = executorLimitCores.map { limitCores =>
       val executorCpuLimitQuantity = new QuantityBuilder(false)
         .withAmount(limitCores)
         .build()
-      new ContainerBuilder(executorContainer)
+      new ContainerBuilder(executorContainerWithVolumes)
         .editResources()
         .addToLimits("cpu", executorCpuLimitQuantity)
         .endResources()
         .build()
-    }.getOrElse(executorContainer)
+    }.getOrElse(executorContainerWithVolumes)
 
     val (maybeSecretsMountedPod, maybeSecretsMountedContainer) =
       mountSecretsBootstrap.map { bootstrap =>
-        (bootstrap.addSecretVolumes(executorPod), bootstrap.mountSecrets(containerWithLimitCores))
-      }.getOrElse((executorPod, containerWithLimitCores))
+        (bootstrap.addSecretVolumes(executorPodWithVolumes),
+          bootstrap.mountSecrets(containerWithLimitCores))
+      }.getOrElse((executorPodWithVolumes, containerWithLimitCores))
 
 
     new PodBuilder(maybeSecretsMountedPod)

resource-managers/kubernetes/core/src/test/scala/org/apache/spark/scheduler/cluster/k8s/ExecutorPodFactorySuite.scala

@@ -167,6 +167,53 @@ class ExecutorPodFactorySuite extends SparkFunSuite with BeforeAndAfter with Bef
     checkOwnerReferences(executor, driverPodUid)
   }
 
+  test("single executor hostPath volume gets mounted") {
+    val conf = baseConf.clone()
+    conf.set(KUBERNETES_EXECUTOR_VOLUMES, "/tmp/mount:/opt/mount")
+    val factory = new ExecutorPodFactory(conf, None)
+
+    val executor = factory.createExecutorPod(
+      "1", "dummy", "dummy", Seq[(String, String)](), driverPod, Map[String, Int]())
+
+    assert(executor.getSpec.getContainers.size() === 1)
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.size() === 1)
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.get(0).getName
+      === "hostPath-volume-0")
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.get(0)
+      .getMountPath === "/opt/mount")
+
+    assert(executor.getSpec.getVolumes.size() === 1)
+    assert(executor.getSpec.getVolumes.get(0).getHostPath.getPath === "/tmp/mount")
+
+    checkOwnerReferences(executor, driverPodUid)
+  }
+
+  test("multiple executor hostPath volumes get mounted") {
+    val conf = baseConf.clone()
+    conf.set(KUBERNETES_EXECUTOR_VOLUMES, "/tmp/mount1:/opt/mount1,/tmp/mount2:/opt/mount2")
+    val factory = new ExecutorPodFactory(conf, None)
+
+    val executor = factory.createExecutorPod(
+      "1", "dummy", "dummy", Seq[(String, String)](), driverPod, Map[String, Int]())
+
+    assert(executor.getSpec.getContainers.size() === 1)
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.size() === 2)
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.get(0).getName
+      === "hostPath-volume-0")
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.get(1).getName
+      === "hostPath-volume-1")
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.get(0)
+      .getMountPath === "/opt/mount1")
+    assert(executor.getSpec.getContainers.get(0).getVolumeMounts.get(1)
+      .getMountPath === "/opt/mount2")
+
+    assert(executor.getSpec.getVolumes.size() === 2)
+    assert(executor.getSpec.getVolumes.get(0).getHostPath.getPath === "/tmp/mount1")
+    assert(executor.getSpec.getVolumes.get(1).getHostPath.getPath === "/tmp/mount2")
+
+    checkOwnerReferences(executor, driverPodUid)
+  }
+
   // There is always exactly one controller reference, and it points to the driver pod.
   private def checkOwnerReferences(executor: Pod, driverPodUid: String): Unit = {
     assert(executor.getMetadata.getOwnerReferences.size() === 1)