Github user mridulm commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19468#discussion_r153349685
  
    --- Diff: 
resource-managers/kubernetes/core/src/main/scala/org/apache/spark/scheduler/cluster/k8s/KubernetesClusterSchedulerBackend.scala
 ---
    @@ -0,0 +1,432 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
    + * (the "License"); you may not use this file except in compliance with
    + * the License.  You may obtain a copy of the License at
    + *
    + *    http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +package org.apache.spark.scheduler.cluster.k8s
    +
    +import java.io.Closeable
    +import java.net.InetAddress
    +import java.util.concurrent.{ConcurrentHashMap, ExecutorService, 
ScheduledExecutorService, TimeUnit}
    +import java.util.concurrent.atomic.{AtomicInteger, AtomicLong, 
AtomicReference}
    +import javax.annotation.concurrent.GuardedBy
    +
    +import io.fabric8.kubernetes.api.model._
    +import io.fabric8.kubernetes.client.{KubernetesClient, 
KubernetesClientException, Watcher}
    +import io.fabric8.kubernetes.client.Watcher.Action
    +import scala.collection.JavaConverters._
    +import scala.collection.mutable
    +import scala.concurrent.{ExecutionContext, Future}
    +
    +import org.apache.spark.SparkException
    +import org.apache.spark.deploy.k8s.Config._
    +import org.apache.spark.deploy.k8s.Constants._
    +import org.apache.spark.rpc.{RpcAddress, RpcEndpointAddress, RpcEnv}
    +import org.apache.spark.scheduler.{ExecutorExited, SlaveLost, 
TaskSchedulerImpl}
    +import org.apache.spark.scheduler.cluster.{CoarseGrainedSchedulerBackend, 
SchedulerBackendUtils}
    +import org.apache.spark.util.Utils
    +
    +private[spark] class KubernetesClusterSchedulerBackend(
    +    scheduler: TaskSchedulerImpl,
    +    rpcEnv: RpcEnv,
    +    executorPodFactory: ExecutorPodFactory,
    +    kubernetesClient: KubernetesClient,
    +    allocatorExecutor: ScheduledExecutorService,
    +    requestExecutorsService: ExecutorService)
    +  extends CoarseGrainedSchedulerBackend(scheduler, rpcEnv) {
    +
    +  import KubernetesClusterSchedulerBackend._
    +
    +  private val EXECUTOR_ID_COUNTER = new AtomicLong(0L)
    +  private val RUNNING_EXECUTOR_PODS_LOCK = new Object
    +  @GuardedBy("RUNNING_EXECUTOR_PODS_LOCK")
    +  private val runningExecutorsToPods = new mutable.HashMap[String, Pod]
    +  private val executorPodsByIPs = new ConcurrentHashMap[String, Pod]()
    +  private val podsWithKnownExitReasons = new ConcurrentHashMap[String, 
ExecutorExited]()
    +  private val disconnectedPodsByExecutorIdPendingRemoval = new 
ConcurrentHashMap[String, Pod]()
    +
    +  private val kubernetesNamespace = conf.get(KUBERNETES_NAMESPACE)
    +
    +  private val kubernetesDriverPodName = conf
    +    .get(KUBERNETES_DRIVER_POD_NAME)
    +    .getOrElse(throw new SparkException("Must specify the driver pod 
name"))
    +  private implicit val requestExecutorContext = 
ExecutionContext.fromExecutorService(
    +    requestExecutorsService)
    +
    +  private val driverPod = kubernetesClient.pods()
    +    .inNamespace(kubernetesNamespace)
    +    .withName(kubernetesDriverPodName)
    +    .get()
    +
    +  protected override val minRegisteredRatio =
    +    if 
(conf.getOption("spark.scheduler.minRegisteredResourcesRatio").isEmpty) {
    +      0.8
    +    } else {
    +      super.minRegisteredRatio
    +    }
    +
    +  private val executorWatchResource = new AtomicReference[Closeable]
    +  private val totalExpectedExecutors = new AtomicInteger(0)
    +
    +  private val driverUrl = RpcEndpointAddress(
    +    conf.get("spark.driver.host"),
    +    conf.getInt("spark.driver.port", DEFAULT_DRIVER_PORT),
    +    CoarseGrainedSchedulerBackend.ENDPOINT_NAME).toString
    +
    +  private val initialExecutors = 
SchedulerBackendUtils.getInitialTargetExecutorNumber(conf)
    +
    +  private val podAllocationInterval = 
conf.get(KUBERNETES_ALLOCATION_BATCH_DELAY)
    +
    +  private val podAllocationSize = 
conf.get(KUBERNETES_ALLOCATION_BATCH_SIZE)
    +
    +  private val allocatorRunnable = new Runnable {
    +
    +    // Maintains a map of executor id to count of checks performed to 
learn the loss reason
    +    // for an executor.
    +    private val executorReasonCheckAttemptCounts = new 
mutable.HashMap[String, Int]
    +
    +    override def run(): Unit = {
    +      handleDisconnectedExecutors()
    +
    +      val executorsToAllocate = mutable.Map[String, Pod]()
    +      val currentTotalRegisteredExecutors = totalRegisteredExecutors.get
    +      val currentTotalExpectedExecutors = totalExpectedExecutors.get
    +      val currentNodeToLocalTaskCount = getNodesWithLocalTaskCounts()
    +      RUNNING_EXECUTOR_PODS_LOCK.synchronized {
    +        if (currentTotalRegisteredExecutors < runningExecutorsToPods.size) 
{
    +          logDebug("Waiting for pending executors before scaling")
    +        } else if (currentTotalExpectedExecutors <= 
runningExecutorsToPods.size) {
    +          logDebug("Maximum allowed executor limit reached. Not scaling up 
further.")
    +        } else {
    +          for (i <- 0 until math.min(
    +            currentTotalExpectedExecutors - runningExecutorsToPods.size, 
podAllocationSize)) {
    +            val executorId = EXECUTOR_ID_COUNTER.incrementAndGet().toString
    +            val executorPod = executorPodFactory.createExecutorPod(
    +              executorId,
    +              applicationId(),
    +              driverUrl,
    +              conf.getExecutorEnv,
    +              driverPod,
    +              currentNodeToLocalTaskCount)
    +            executorsToAllocate(executorId) = executorPod
    +            logInfo(
    +              s"Requesting a new executor, total executors is now 
${runningExecutorsToPods.size}")
    +          }
    +        }
    +      }
    +
    +      val allocatedExecutors = executorsToAllocate.mapValues { pod =>
    +        Utils.tryLog {
    +          kubernetesClient.pods().create(pod)
    +        }
    +      }
    +
    +      RUNNING_EXECUTOR_PODS_LOCK.synchronized {
    +        allocatedExecutors.map {
    +          case (executorId, attemptedAllocatedExecutor) =>
    +            attemptedAllocatedExecutor.map { successfullyAllocatedExecutor 
=>
    +              runningExecutorsToPods.put(executorId, 
successfullyAllocatedExecutor)
    +            }
    +        }
    +      }
    +    }
    +
    +    def handleDisconnectedExecutors(): Unit = {
    +      // For each disconnected executor, synchronize with the loss reasons 
that may have been found
    +      // by the executor pod watcher. If the loss reason was discovered by 
the watcher,
    +      // inform the parent class with removeExecutor.
    +      disconnectedPodsByExecutorIdPendingRemoval.asScala.foreach {
    +        case (executorId, executorPod) =>
    +          val knownExitReason = Option(podsWithKnownExitReasons.remove(
    +            executorPod.getMetadata.getName))
    +          knownExitReason.fold {
    +            removeExecutorOrIncrementLossReasonCheckCount(executorId)
    +          } { executorExited =>
    +            logWarning(s"Removing executor $executorId with loss reason " 
+ executorExited.message)
    +            removeExecutor(executorId, executorExited)
    +            // We don't delete the pod running the executor that has an 
exit condition caused by
    +            // the application from the Kubernetes API server. This allows 
users to debug later on
    +            // through commands such as "kubectl logs <pod name>" and
    +            // "kubectl describe pod <pod name>". Note that exited 
containers have terminated and
    +            // therefore won't take CPU and memory resources.
    +            // Otherwise, the executor pod is marked to be deleted from 
the API server.
    +            if (executorExited.exitCausedByApp) {
    --- End diff --
    
    Sounds great, as long as spark driver memory is not getting impacted by 
having these around; it should be fine.
    Thanks for clarifying !


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