什么是delegation token
delegation token其實就是hadoop里一種輕量級認證方法，作為kerberos認證的一種補充。理論上只使用kerberos來認證是足夠了，為什么hadoop還要自己開發一套使用delegation token的認證方式呢？這是因為如果在一個很大的分布式系統當中，如果每個節點訪問某個服務的時候都使用kerberos來作為認證方式，那么勢必對KDC造成很大的壓力，KDC就會成為一個系統的瓶頸。
與kerberos的區別
kerberos認證需三方參與，client， kdc， server三方協作完成認證。通常包括三個子過程：
- client向kdc申請TGT（Ticket Granting Ticket），TGT包含client信息及client和KDC之間的 session key兩部分信息，并且使用KDC的master key加密
- client使用TGT向KDC申請訪問某個服務的Ticket，Ticket包含client信息及client和server之間的session key兩部分信息，并且使用server的master key加密。
- client使用Ticket訪問某個服務。
Delegation token的認證只需要兩方參與，client和server。在server端生成token并發送給client端。client使用該token訪問server，server對該token進行認證。
Delegation token可以傳遞給其它服務使用，這也是它叫delegation token的原因。比如在client端獲取到hdfs delegation token后，可以分發到Mapper端和Reducer端。這樣Map，Reduce就不用在通過Kerberos認證而直接使用該token訪問hdfs。同時，delegation token可以指定更新者（renewer），比如yarn，或者自己。token快要過期的時候需要更新，更新的時候只涉及更新者和server端。其它任何使用該token的人都不會受到影響。
delegation token 期限
delegation token有過期時間，需要定期刷新才能保證token有效。但是刷新次數不是無限的，也就是說每個token都有個最大生存時間，超過該時間，該token就失效。比如token每個24小時需要刷新一次，否則就失效。同時每個token最大生命值為7天，那么七天后該token就不能在被使用。
delegation 包含的內容
Token.java
private byte[] identifier;
private byte[] password;
private Text kind;
private Text service;
private TokenRenewer renewer;
其中identifiertoken的標識，password用于server端認證該token。kind參數表示該token的類型，比如HDFS_DELEGATION_TOKEN，service表示該token訪問的服務，比如ha-hdfs:<nameservice>，renewer表示刷新者。
以上幾個部分是client拿到的token包含的內容。token的失效時間、owner、realuser等信息存放在server端。
delegation 生命周期
上圖展示了在yarn應用中，delegation token的生命流程。
1）client端首先通過Kerberos 認證方式訪問namenode，獲取DT（delegation token）
2）client向yarn提交應用，并且把DT傳給RM。同時會指定yarn作為該token的renewer。
3）rm選一個節點啟動Am，隨后AM向RM申請資源，將worker contaiern都啟動。這一步中DT都會分發到相應的container中。
4）所有的工作節點都使用DT去訪問hdfs
5）當工作結束后，RM釋放該DT。
delegation token過期應該怎么辦
delegation token會失效，集群默認配置是renew的間隔為一天，token最大生存時間為7天。對于像mapreduce這種批處理任務可能不會面臨token失效的問題，但對于spark streaming, storm等這種長時運行應用來說，不得不面臨一個問題：token存在最大生命周期。當token達到其最大生命周期的時候，比如七天，所有的工作節點（比如spark streaming的executor）中使用的token都會失效，此時在使用該token去訪問hdfs就會被namenode拒絕，導致應用異常退出。
一種解決思路是將keytab文件分發給Am及每個container，讓am和container去訪問kdc來認證，但這種方式會造成文章開頭所說的問題：對KDC造成很大的訪問壓力，導致KDC會誤認為自己遭受了DDos攻擊，從而影響程序性能。
另一種解決思路是先由client把keytab文件放到hdfs上。然后在Am中使用keytab登錄，并申請delegation token。Am在啟動worker的時候把該token分發給相應的容器。當token快要過期的時候，Am重新登錄一次，并重新獲取delegation token，并告知所有的worker使用更新后的token訪問服務。
spark中怎么解決delegation token過期問題
spark使用的就是第二種解決思路，接下來詳細分析下spark1.6是怎么解決token過期問題的。
spark 為了解決DT失效問題，加了兩個參數"--keytab"和"--principal"，分別指定用于kerberos登錄的keytab文件和principal。spark中用于提交yarn任務的類為Client
org.apache.spark.deploy.yarn.Client
def submitApplication(): ApplicationId = {
var appId: ApplicationId = null
try {
launcherBackend.connect()
// Setup the credentials before doing anything else,
// so we have don't have issues at any point.
setupCredentials()
yarnClient.init(yarnConf)
yarnClient.start()
logInfo("Requesting a new application from cluster with %d NodeManagers"
.format(yarnClient.getYarnClusterMetrics.getNumNodeManagers))
// Get a new application from our RM
val newApp = yarnClient.createApplication()
val newAppResponse = newApp.getNewApplicationResponse()
appId = newAppResponse.getApplicationId()
reportLauncherState(SparkAppHandle.State.SUBMITTED)
launcherBackend.setAppId(appId.toString())
// Verify whether the cluster has enough resources for our AM
verifyClusterResources(newAppResponse)
// Set up the appropriate contexts to launch our AM
val containerContext = createContainerLaunchContext(newAppResponse)
val appContext = createApplicationSubmissionContext(newApp, containerContext)
// Finally, submit and monitor the application
logInfo(s"Submitting application ${appId.getId} to ResourceManager")
yarnClient.submitApplication(appContext)
appId
} catch {
case e: Throwable =>
if (appId != null) {
cleanupStagingDir(appId)
}
throw e
}
submitApplication是提交yarn任務的入口，該函數的最開始調用了setupCredentials函數用于設置Credential。
def setupCredentials(): Unit = {
loginFromKeytab = args.principal != null || sparkConf.contains("spark.yarn.principal")
...
// Defensive copy of the credentials
credentials = new Credentials(UserGroupInformation.getCurrentUser.getCredentials)
}
先判斷參數中是否包含“--principal”，如果包含，則成員變量logingFromKeytab置為true。這個成員變量用于后面的一些判斷。另外就是獲取當前ugi中包含的Credentials對象。
設置完credentials后，調用yarn的接口創建一個Application，并取得appid，然后需要創建containerLaunchContext，這是走的yarn程序的標準流程，進一步分析該函數
private def createContainerLaunchContext(newAppResponse: GetNewApplicationResponse)
: ContainerLaunchContext = {
logInfo("Setting up container launch context for our AM")
val appId = newAppResponse.getApplicationId
val appStagingDir = getAppStagingDir(appId)
val pySparkArchives =
if (sparkConf.getBoolean("spark.yarn.isPython", false)) {
findPySparkArchives()
} else {
Nil
}
val launchEnv = setupLaunchEnv(appStagingDir, pySparkArchives)
val localResources = prepareLocalResources(appStagingDir, pySparkArchives)
// Set the environment variables to be passed on to the executors.
distCacheMgr.setDistFilesEnv(launchEnv)
distCacheMgr.setDistArchivesEnv(launchEnv)
val amContainer = Records.newRecord(classOf[ContainerLaunchContext])
amContainer.setLocalResources(localResources.asJava)
amContainer.setEnvironment(launchEnv.asJava)
...
setupSecurityToken(amContainer)
amContainer
}
這個函數很長，省略了一些代碼，主要是設置container啟動的命令行，環境變量，classpath之類的東西。在setupLaunchEnv函數里設置了后期在Am中用于通知executor的credentials文件
private def setupLaunchEnv(
stagingDir: String,
pySparkArchives: Seq[String]): HashMap[String, String] = {
...
if (loginFromKeytab) {
val remoteFs = FileSystem.get(hadoopConf)
val stagingDirPath = new Path(remoteFs.getHomeDirectory, stagingDir)
val credentialsFile = "credentials-" + UUID.randomUUID().toString
sparkConf.set(
"spark.yarn.credentials.file", new Path(stagingDirPath, credentialsFile).toString)
logInfo(s"Credentials file set to: $credentialsFile")
val renewalInterval = getTokenRenewalInterval(stagingDirPath)
sparkConf.set("spark.yarn.token.renewal.interval", renewalInterval.toString)
}
...
}
先判斷loginFromKeytab是否為true。在前面我們看到只要在命令行中使用了"--principal"參數，loginFromKeytab就為true，這里聲明了用于存放token的文件位置，默認為hdfs上位于/user/{user}/.sparkSgating/{appid}目錄下的以credentials開頭的文件。并把該文件位置放在sparkConf中，key為“spark.yarn.credentials.file”，這在后邊會用到。同時這里獲取了DT renew的間隔。也同樣放在sparkConf中，key為“spark.yarn.token.renewal.interval”。
設置完登錄環境后，進入到另一個函數prepareLocalResources，這個函數里邊有一個關鍵的步驟：獲取hdfs
delegation token
YarnSparkHadoopUtil.get.obtainTokensForNamenodes(nns, hadoopConf, credentials)
def obtainTokensForNamenodes(
paths: Set[Path],
conf: Configuration,
creds: Credentials,
renewer: Option[String] = None
): Unit = {
if (UserGroupInformation.isSecurityEnabled()) {
val delegTokenRenewer = renewer.getOrElse(getTokenRenewer(conf))
paths.foreach { dst =>
val dstFs = dst.getFileSystem(conf)
logInfo("getting token for namenode: " + dst)
dstFs.addDelegationTokens(delegTokenRenewer, creds)
}
}
}
這個函數用于向namenode索取hdfs delegation token，并把該token添加到Credentials對象中。前面我們講過，credentiasl對象的初值為UserGroupInformation.getCurrentUser.getCredentials, 而ugi中默認是不包含hdfs delegation token的。因此通過該函數會吧hdfs delegation token添加到credentials中。
然后回到createContainerLaunchContext， 準備工作都做好后，創建了amContainer，并調用setupSecurityToken函數給amContainer設置剛剛獲取到的token。所以當Am起來后不需要通過kerberos認證，可以直接使用hdfs delegation token與namenode交互。
private def setupSecurityToken(amContainer: ContainerLaunchContext): Unit = {
val dob = new DataOutputBuffer
credentials.writeTokenStorageToStream(dob)
amContainer.setTokens(ByteBuffer.wrap(dob.getData))
}
至此，有關token的東西都準備好了，調用yarnClient.submitApplication(appContext)向yarn提交任務。yarn在收到請求后會先找一個機器啟動AmContainer。yarn啟動container的命令其實就是client傳給yarn的。大概就是“bin/java xxx org.apache.spark.deploy.yarn.ApplicationMaster xxx”。Am的入口為ApplicationMaster的run函數。
org.apache.spark.deploy.yarn.ApplicationMaster
final def run(): Int = {
try {
...
// If the credentials file config is present, we must periodically renew tokens. So create
// a new AMDelegationTokenRenewer
if (sparkConf.contains("spark.yarn.credentials.file")) {
delegationTokenRenewerOption = Some(new AMDelegationTokenRenewer(sparkConf, yarnConf))
// If a principal and keytab have been set, use that to create new credentials for executors
// periodically
delegationTokenRenewerOption.foreach(_.scheduleLoginFromKeytab())
}
if (isClusterMode) {
runDriver(securityMgr)
} else {
runExecutorLauncher(securityMgr)
}
} catch {
case e: Exception =>
// catch everything else if not specifically handled
logError("Uncaught exception: ", e)
finish(FinalApplicationStatus.FAILED,
ApplicationMaster.EXIT_UNCAUGHT_EXCEPTION,
"Uncaught exception: " + e)
}
exitCode
}
這里看到了一個熟悉的配置“spark.yarn.credentials.file”， 還記得我們之前講過該參數被設置為什么了嗎？就是Am用于保存token文件的位置。所以，如果spark submit啟動的時候傳遞了"--principal"參數，就會在sparkConf中生成一個“spark.yarn.credentials.file”配置，如果sparkConf中有“spark.yarn.credentials.file”配置，在AM中，也就是run函數中，會生成一個AMDelegationTokenRenewer對象。從名字也可以看出，這個對象就負責定期的更新token，將token寫入到一個hdfs文件，然后executor從該文件中獲取新的token從而防止token過期的作用了。
AMDelegationTokenRenewer
private[spark] def scheduleLoginFromKeytab(): Unit = {
val principal = sparkConf.get("spark.yarn.principal")
val keytab = sparkConf.get("spark.yarn.keytab")
/**
* Schedule re-login and creation of new tokens. If tokens have already expired, this method
* will synchronously create new ones.
*/
def scheduleRenewal(runnable: Runnable): Unit = {
val credentials = UserGroupInformation.getCurrentUser.getCredentials
val renewalInterval = hadoopUtil.getTimeFromNowToRenewal(sparkConf, 0.75, credentials)
// Run now!
if (renewalInterval <= 0) {
logInfo("HDFS tokens have expired, creating new tokens now.")
runnable.run()
} else {
logInfo(s"Scheduling login from keytab in $renewalInterval millis.")
delegationTokenRenewer.schedule(runnable, renewalInterval, TimeUnit.MILLISECONDS)
}
}
// This thread periodically runs on the driver to update the delegation tokens on HDFS.
val driverTokenRenewerRunnable =
new Runnable {
override def run(): Unit = {
try {
writeNewTokensToHDFS(principal, keytab)
cleanupOldFiles()
} catch {
case e: Exception =>
// Log the error and try to write new tokens back in an hour
logWarning("Failed to write out new credentials to HDFS, will try again in an " +
"hour! If this happens too often tasks will fail.", e)
delegationTokenRenewer.schedule(this, 1, TimeUnit.HOURS)
return
}
scheduleRenewal(this)
}
}
// Schedule update of credentials. This handles the case of updating the tokens right now
// as well, since the renenwal interval will be 0, and the thread will get scheduled
// immediately.
scheduleRenewal(driverTokenRenewerRunnable)
}
首先判斷token是否快要過期了，如果是，則調用writeNewTokensToHDFS函數獲取新的token，并寫到hdfs上。否則，生成一個調度任務再一段時間后重新判斷。
private def writeNewTokensToHDFS(principal: String, keytab: String): Unit = {
// Keytab is copied by YARN to the working directory of the AM, so full path is
// not needed.
// HACK:
// HDFS will not issue new delegation tokens, if the Credentials object
// passed in already has tokens for that FS even if the tokens are expired (it really only
// checks if there are tokens for the service, and not if they are valid). So the only real
// way to get new tokens is to make sure a different Credentials object is used each time to
// get new tokens and then the new tokens are copied over the the current user's Credentials.
// So:
// - we login as a different user and get the UGI
// - use that UGI to get the tokens (see doAs block below)
// - copy the tokens over to the current user's credentials (this will overwrite the tokens
// in the current user's Credentials object for this FS).
// The login to KDC happens each time new tokens are required, but this is rare enough to not
// have to worry about (like once every day or so). This makes this code clearer than having
// to login and then relogin every time (the HDFS API may not relogin since we don't use this
// UGI directly for HDFS communication.
logInfo(s"Attempting to login to KDC using principal: $principal")
//1）重新登錄kdc
val keytabLoggedInUGI = UserGroupInformation.loginUserFromKeytabAndReturnUGI(principal, keytab)
logInfo("Successfully logged into KDC.")
val tempCreds = keytabLoggedInUGI.getCredentials
val credentialsPath = new Path(credentialsFile)
val dst = credentialsPath.getParent
//2）使用新的登錄身份信息向namenode拿hdfs delegation token，并添加到tempCreds中
keytabLoggedInUGI.doAs(new PrivilegedExceptionAction[Void] {
// Get a copy of the credentials
override def run(): Void = {
val nns = YarnSparkHadoopUtil.get.getNameNodesToAccess(sparkConf) + dst
hadoopUtil.obtainTokensForNamenodes(nns, freshHadoopConf, tempCreds)
null
}
})
// Add the temp credentials back to the original ones.
//3)將新獲取的token添加到當前登錄用戶中
UserGroupInformation.getCurrentUser.addCredentials(tempCreds)
val remoteFs = FileSystem.get(freshHadoopConf)
// If lastCredentialsFileSuffix is 0, then the AM is either started or restarted. If the AM
// was restarted, then the lastCredentialsFileSuffix might be > 0, so find the newest file
// and update the lastCredentialsFileSuffix.
if (lastCredentialsFileSuffix == 0) {
hadoopUtil.listFilesSorted(
remoteFs, credentialsPath.getParent,
credentialsPath.getName, SparkHadoopUtil.SPARK_YARN_CREDS_TEMP_EXTENSION)
.lastOption.foreach { status =>
lastCredentialsFileSuffix = hadoopUtil.getSuffixForCredentialsPath(status.getPath)
}
}
val nextSuffix = lastCredentialsFileSuffix + 1
val tokenPathStr =
credentialsFile + SparkHadoopUtil.SPARK_YARN_CREDS_COUNTER_DELIM + nextSuffix
val tokenPath = new Path(tokenPathStr)
val tempTokenPath = new Path(tokenPathStr + SparkHadoopUtil.SPARK_YARN_CREDS_TEMP_EXTENSION)
logInfo("Writing out delegation tokens to " + tempTokenPath.toString)
val credentials = UserGroupInformation.getCurrentUser.getCredentials
//4）將credentials信息寫到目標文件中
credentials.writeTokenStorageFile(tempTokenPath, freshHadoopConf)
logInfo(s"Delegation Tokens written out successfully. Renaming file to $tokenPathStr")
remoteFs.rename(tempTokenPath, tokenPath)
logInfo("Delegation token file rename complete.")
lastCredentialsFileSuffix = nextSuffix
}
更新token的代碼都在這個函數里了。其實就包括以下幾個步驟
1）使用keytab和principal重新登錄kerberos，并獲取登錄的ugi信息：keytabLoggedInUGI，注意，這里僅僅是kerberos的一個認證過程，還并不涉及到hdfs delegation token的東西，即keytabLoggedInUGI 中并不包含token信息。loginUserFromKeytabAndReturnUGI函數回返回一個新的用戶對象，而不會影響當前登錄的用戶
2）獲取keytabLoggedInUGI 中的credentials對象，然后使用keytabLoggedInUGI 身份去向namenode獲取新的hdfs delegation token。并將token添加到一個臨時的credentials對象中
3）將臨時的credentials對象中的token添加到當前登錄的ugi中。此時Am中使用token已經被更新，所以Am不會出現token expired問題，但是還需要把token更新到executor中。
4）生成token的存放目錄，token存放目錄為/user/{user}/.sparkStaging/${appid}, token文件名格式為“credentials-UUID-suffix”， suffix為后綴，按文件個數遞增。token file默認保留五天。
至此，Am端token已經寫到hdfs文件了。接下來就是executor端怎么讀到最新的token文件，并把token更新到自己的ugi當中。
Executor啟動過程這里就不在分析，主要是在AM當中會生成executor的啟動信息及上下文，并發給NodeManager，由NodeManager來啟動executor的container。在spark中，最終代表executor的類為：CoarseGrainedExecutorBackend
CoarseGrainedExecutorBackend
private def run(
driverUrl: String,
executorId: String,
hostname: String,
cores: Int,
appId: String,
workerUrl: Option[String],
userClassPath: Seq[URL]) {
...
if (driverConf.contains("spark.yarn.credentials.file")) {
logInfo("Will periodically update credentials from: " +
driverConf.get("spark.yarn.credentials.file"))
SparkHadoopUtil.get.startExecutorDelegationTokenRenewer(driverConf)
}
...
}
}
這里也是先判斷在sparkConf中是否有"spark.yarn.credentials.file"配置，如果有，會生成一個ExecutorDelegationTokenUpdater對象，并調用其updateCredentialsIfRequired更新token
ExecutorDelegationTokenUpdater
try {
val credentialsFilePath = new Path(credentialsFile)
val remoteFs = FileSystem.get(freshHadoopConf)
SparkHadoopUtil.get.listFilesSorted(
remoteFs, credentialsFilePath.getParent,
credentialsFilePath.getName, SparkHadoopUtil.SPARK_YARN_CREDS_TEMP_EXTENSION)
.lastOption.foreach { credentialsStatus =>
val suffix = SparkHadoopUtil.get.getSuffixForCredentialsPath(credentialsStatus.getPath)
if (suffix > lastCredentialsFileSuffix) {
logInfo("Reading new delegation tokens from " + credentialsStatus.getPath)
val newCredentials = getCredentialsFromHDFSFile(remoteFs, credentialsStatus.getPath)
lastCredentialsFileSuffix = suffix
UserGroupInformation.getCurrentUser.addCredentials(newCredentials)
logInfo("Tokens updated from credentials file.")
} else {
// Check every hour to see if new credentials arrived.
logInfo("Updated delegation tokens were expected, but the driver has not updated the " +
"tokens yet, will check again in an hour.")
delegationTokenRenewer.schedule(executorUpdaterRunnable, 1, TimeUnit.HOURS)
return
}
}
val timeFromNowToRenewal =
SparkHadoopUtil.get.getTimeFromNowToRenewal(
sparkConf, 0.8, UserGroupInformation.getCurrentUser.getCredentials)
if (timeFromNowToRenewal <= 0) {
// We just checked for new credentials but none were there, wait a minute and retry.
// This handles the shutdown case where the staging directory may have been removed(see
// SPARK-12316 for more details).
delegationTokenRenewer.schedule(executorUpdaterRunnable, 1, TimeUnit.MINUTES)
} else {
logInfo(s"Scheduling token refresh from HDFS in $timeFromNowToRenewal millis.")
delegationTokenRenewer.schedule(
executorUpdaterRunnable, timeFromNowToRenewal, TimeUnit.MILLISECONDS)
}
} catch {
// Since the file may get deleted while we are reading it, catch the Exception and come
// back in an hour to try again
case NonFatal(e) =>
logWarning("Error while trying to update credentials, will try again in 1 hour", e)
delegationTokenRenewer.schedule(executorUpdaterRunnable, 1, TimeUnit.HOURS)
}
這個函數就是executor端更新token的整個過程，包括幾個步驟
1）獲取hdfs上保存credentials目錄下的最近更新的文件，并取出其suffix，與當前程序中保存的lastCredentialsFileSuffix 比較，如果比lastCredentialsFileSuffix 大，則表示AM端更新了token，需要重新讀取token并更新。
2）如果Am端還沒更新，則過一小時重試
3）token更新完后，會再次判斷下次待更新的時間，并生成一個調度任務，到期執行更新操作。
在executor端更新其實就是把hdfs上的credentials文件讀取出來，使用 UserGroupInformation.getCurrentUser.addCredentials(newCredentials)函數對當前的ugi添加新的token信息就可以了。
至此，spark上解決hdfs delegation token過期問題就分析完了。整個過程類似與下面這張圖：
總結下來就是在Am端更新token信息，并把更新后的token寫到hdfs，在executor端讀取hdfs上更新的token，并更新到自己的ugi當中。按理說這樣能解決token過期的問題了，但是用過spark streaming的同學可能會遇到一個奇怪的問題，即使在提交任務的時候帶上了"--principal"參數，還是會遇到hdfs delegation token 過期的問題，那又是怎么一會事呢？下面繼續分析hdfs的一個bug。
hdfs delegation token bug
如上文分析，Spark在Am端會去更新token，因此理論上來講應該不會出現token過期問題了，但在我們使用過程中還是會出現token過期的情況，網上查了后說是hfds上的一個bug導致:hdfs-9276
理解這個bug要先知道一個概念，即Token的service字段是client從server端獲取token后添加的，client用于區分不同服務的token，在server端根本沒有service字段的概念。客戶端通過FileSystem.addDelegationTokens函數向namenode申請hdfs delegation token。當從server端申請到token后，會給token設置service字段：
DFSClient.java
public Token<DelegationTokenIdentifier> getDelegationToken(Text renewer)
throws IOException {
assert dtService != null;
Token<DelegationTokenIdentifier> token =
namenode.getDelegationToken(renewer);
if (token != null) {
token.setService(this.dtService);
LOG.info("Created " + DelegationTokenIdentifier.stringifyToken(token));
} else {
LOG.info("Cannot get delegation token from " + renewer);
}
return token;
}
這里將service字段設置為dtService。在HA這種情況下，客戶端使用nameservice訪問hdfs，所以dtService的值為：ha-hdfs:<nameservice>。
這個service我們暫且稱之為logicService。但是，client必須使用IP:PORT訪問server。當client確定active的namenode后，怎么確定使用哪個token來和server端認證呢？之前講過token的service字段用于區分不同的server，但是該字段里并不包含具體的ip和端口。為了解決這個問題，其實每次在new 一個DFSClient實例時，會把token拷貝兩份，并把里面的service字段替換成具體的ip和端口：
HAUtil.java
public static void cloneDelegationTokenForLogicalUri(
UserGroupInformation ugi, URI haUri,
Collection<InetSocketAddress> nnAddrs) {
// this cloning logic is only used by hdfs
Text haService = HAUtil.buildTokenServiceForLogicalUri(haUri,
HdfsConstants.HDFS_URI_SCHEME);
Token<DelegationTokenIdentifier> haToken =
tokenSelector.selectToken(haService, ugi.getTokens());
if (haToken != null) {
for (InetSocketAddress singleNNAddr : nnAddrs) {
// this is a minor hack to prevent physical HA tokens from being
// exposed to the user via UGI.getCredentials(), otherwise these
// cloned tokens may be inadvertently propagated to jobs
Token<DelegationTokenIdentifier> specificToken =
new Token.PrivateToken<DelegationTokenIdentifier>(haToken);
SecurityUtil.setTokenService(specificToken, singleNNAddr);
Text alias = new Text(
buildTokenServicePrefixForLogicalUri(HdfsConstants.HDFS_URI_SCHEME)
+ "http://" + specificToken.getService());
ugi.addToken(alias, specificToken);
LOG.debug("Mapped HA service delegation token for logical URI " +
haUri + " to namenode " + singleNNAddr);
}
} else {
LOG.debug("No HA service delegation token found for logical URI " +
haUri);
}
}
這樣一來，在client端，每一個token其實就有三個拷貝，分別為一個HA token，和兩個對應到具體namenode的namenode token。于是，client想和哪個namenode通信就能選擇到相應的token了。
那hdfs-9276這個bug就很明顯了，意思是當用戶使用UserGroupInformation.getCurrentUser().addCredentials(credentials)方法更新token時，只能更新HA token，并不能更新兩個namenode token。所以當client使用namenode 的ip和port選擇到某個namenode token時，該token其實還是老的token，并沒有被更新，因此使用該token去訪問server端，就會被server拒絕，并提示token過期異常。
所以9276的patch把這個問題解決了（代碼就不分析，感興趣的可以自己去看下），當用戶addCredentials的時候，會把HA token對應的兩個namenode token也更新。細心的讀者應該發現，當每次new一個DFSClient實例的時候，內部就會把HA token拷貝兩份，生成新的兩個namenode token，因此如果每次都new 一個DFSClient是可以繞過9276描述的問題的。
其實spark也是嘗試這么做的，回到spark 在excutor端更新token的過程：
ExecutorDelegationTokenUpdater
try {
val credentialsFilePath = new Path(credentialsFile)
//此處獲取了一個新的FileSystem對象，但此時ugi中的HA token還沒有被更新
val remoteFs = FileSystem.get(freshHadoopConf)
SparkHadoopUtil.get.listFilesSorted(
remoteFs, credentialsFilePath.getParent,
credentialsFilePath.getName, SparkHadoopUtil.SPARK_YARN_CREDS_TEMP_EXTENSION)
.lastOption.foreach { credentialsStatus =>
val suffix = SparkHadoopUtil.get.getSuffixForCredentialsPath(credentialsStatus.getPath)
if (suffix > lastCredentialsFileSuffix) {
logInfo("Reading new delegation tokens from " + credentialsStatus.getPath)
//從hdfs中讀取HA token
val newCredentials = getCredentialsFromHDFSFile(remoteFs, credentialsStatus.getPath)
lastCredentialsFileSuffix = suffix
//把新的HA token更新到ugi當中
UserGroupInformation.getCurrentUser.addCredentials(newCredentials)
logInfo("Tokens updated from credentials file.")
} else {
// Check every hour to see if new credentials arrived.
logInfo("Updated delegation tokens were expected, but the driver has not updated the " +
"tokens yet, will check again in an hour.")
delegationTokenRenewer.schedule(executorUpdaterRunnable, 1, TimeUnit.HOURS)
return
}
}
val timeFromNowToRenewal =
SparkHadoopUtil.get.getTimeFromNowToRenewal(
sparkConf, 0.8, UserGroupInformation.getCurrentUser.getCredentials)
if (timeFromNowToRenewal <= 0) {
// We just checked for new credentials but none were there, wait a minute and retry.
// This handles the shutdown case where the staging directory may have been removed(see
// SPARK-12316 for more details).
delegationTokenRenewer.schedule(executorUpdaterRunnable, 1, TimeUnit.MINUTES)
} else {
//更新完token后，馬上調度了下一個更新任務，而這個任務要在更新的token快要過期時才會執行
logInfo(s"Scheduling token refresh from HDFS in $timeFromNowToRenewal millis.")
delegationTokenRenewer.schedule(
executorUpdaterRunnable, timeFromNowToRenewal, TimeUnit.MILLISECONDS)
}
} catch {
// Since the file may get deleted while we are reading it, catch the Exception and come
// back in an hour to try again
case NonFatal(e) =>
logWarning("Error while trying to update credentials, will try again in 1 hour", e)
delegationTokenRenewer.schedule(executorUpdaterRunnable, 1, TimeUnit.HOURS)
}
在函數的開始獲使用FileSystem.get(freshHadoopConf)獲取remoteFs對象，其中freshHadoopConf的"fs.hdfs.impl.disable.cache"設置為true，表示新生產一個FileSystem對象。這里其實很明顯就是想讓繞過9276 bug。但是很可惜，用的地方不對。在新生產這個對象的時候，ugi中保存的token其實還并沒有被更新。隨后讀取hdfs中新的token，并更新到ugi當中。然后便調度下一個任務了。可以看到在更新token后，沒有在new 一個FileSystem，所以ugi中的namenode token就得不到更新，因此還是會出現token過期問題。
hdfs delegation token過期問題分析到此結束。
