Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/4688#discussion_r28285643
--- Diff:
yarn/src/main/scala/org/apache/spark/deploy/yarn/AMDelegationTokenRenewer.scala
---
@@ -0,0 +1,211 @@
+/*
+ * 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.deploy.yarn
+
+import java.io.{DataOutputStream, ByteArrayOutputStream}
+import java.nio.ByteBuffer
+import java.util.concurrent.{Executors, TimeUnit}
+
+import akka.actor.ActorSelection
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.fs.{FileStatus, FileSystem, Path}
+import org.apache.hadoop.security.UserGroupInformation
+
+import org.apache.spark.deploy.SparkHadoopUtil
+import org.apache.spark.rpc.RpcEndpointRef
+import
org.apache.spark.scheduler.cluster.CoarseGrainedClusterMessages.NewTokens
+import org.apache.spark.{Logging, SparkConf}
+import org.apache.spark.util.{SerializableBuffer, Utils}
+
+/*
+ * The following methods are primarily meant to make sure long-running
apps like Spark
+ * Streaming apps can run without interruption while writing to secure
HDFS. The
+ * scheduleLoginFromKeytab method is called on the driver when the
+ * CoarseGrainedScheduledBackend starts up. This method wakes up a thread
that logs into the KDC
+ * once 75% of the expiry time of the original delegation tokens used for
the container
+ * has elapsed. It then creates new delegation tokens and writes them to
HDFS in a
+ * pre-specified location - the prefix of which is specified in the
sparkConf by
+ * spark.yarn.credentials.file (so the file(s) would be named c-1, c-2
etc. - each update goes
+ * to a new file, with a monotonically increasing suffix). After this, the
credentials are
+ * updated once 75% of the new tokens validity has elapsed.
+ *
+ * On the executor side, the updateCredentialsIfRequired method is called
once 80% of the
+ * validity of the original tokens has elapsed. At that time the executor
finds the
+ * credentials file with the latest timestamp and checks if it has read
those credentials
+ * before (by keeping track of the suffix of the last file it read). If a
new file has
+ * appeared, it will read the credentials and update the currently running
UGI with it. This
+ * process happens again once 80% of the validity of this has expired.
+ */
+class AMDelegationTokenRenewer(sparkConf: SparkConf, hadoopConf:
Configuration) extends Logging {
+
+ private var lastCredentialsFileSuffix = 0
+
+ private lazy val delegationTokenRenewer =
+ Executors.newSingleThreadScheduledExecutor(
+ Utils.namedThreadFactory("Delegation Token Refresh Thread"))
+
+ private var loggedInViaKeytab = false
+ var driverEndPoint: RpcEndpointRef = null
+
+ private lazy val hadoopUtil = YarnSparkHadoopUtil.get
+
+ /**
+ * Schedule a login from the keytab and principal set using the
--principal and --keytab
+ * arguments to spark-submit. This login happens only when the
credentials of the current user
+ * are about to expire. This method reads SPARK_PRINCIPAL and
SPARK_KEYTAB from the environment
+ * to do the login. This method is a no-op in non-YARN mode.
+ */
+ private[spark] def scheduleLoginFromKeytab(): Unit = {
+ sparkConf.getOption("spark.yarn.principal").foreach { principal =>
--- End diff --
Same thing here. Could you instead have the caller store this instance in
an `Option` when it's not needed?
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