1. 背景
https://blog.51cto.com/u_15327484/8153877文章中介绍了Hadoop中使用kerberos机制进行认证。在客户端初次访问服务端时，通过JAAS获取TGT，再通过GSSAPI on SASL获取service ticket完成认证。
在用户向Yarn提交作业时，如果作业有上万个container，每个container都会访问HDFS的NameNode，那么就有两个问题：
- 要将keytab文件发送给每一个container，让每个container进行认证，这容易造成keytab文件泄漏，产生安全风险。
- 每个container访问NameNode前，都会向KDC进行认证，可能造成KDC性能瓶颈。
为了解决这个问题，Haodop引入Delegation Token机制，当客户端和服务端进行Kerberos认证后，立刻申请Delegation Token，后续客户端使用Token向NameNode进行认证。并且，Token会通过Yarn框架传递到每个container中，这些container直接通过token认证NameNode，无需新建认证信息。
2. Delegation Token介绍
Yarn作业中的认证执行流程如下：
- 客户端通过kerberos认证方式访问namenode，认证结束后申请Delegation Token。
- 客户端提交作业，请求中携带token信息。
- resourcemanager启动contaienr时，携带token信息。
- container访问NameNode时，使用该token进行认证。
- Yarn通过定时线程向Hdfs请求更新token。
- KMS是存储密钥信息的，一般生产环境没有启动该服务，可以暂时不管。
本文将介绍MapReduce作业请求NameNode的Delegation Token过程，并且介绍Resource Manager更新Delegation Token过程。注意，作业在提交时，还会申请resoureManager、historyServer等服务的Delegation Token，这些Delegation Token的处理过程和NameNode的Delegation Token处理过程一致，不再赘述。
3. MapReduce作业客户端请求NameNode创建Delegation Token
在执行MapReduce代码时，客户端会执行getSplits方法将输入数据切分成多个splits。切分前，会访问作业处理的所有HDFS文件信息：
public InputSplit[] getSplits(JobConf job, int numSplits)
throws IOException {
StopWatch sw = new StopWatch().start();
FileStatus[] stats = listStatus(job);
//切分逻辑
}
listStatus在访问HDFS文件前，会从NameNode中获取Delegation Token。在输入参数中，将job.getCredentials()表示当前作业对应的credentials，作业获取的delegation token会保存在这个对象中：
protected FileStatus[] listStatus(JobConf job) throws IOException {
Path[] dirs = getInputPaths(job);
if (dirs.length == 0) {
throw new IOException("No input paths specified in job");
}
// get tokens for all the required FileSystems..
//获取Delegation Token
TokenCache.obtainTokensForNamenodes(job.getCredentials(), dirs, job);
//访问所有HDFS文件
}
TokenCache.obtainTokensForNamenodesInternal获取MR作业中要访问的所有HDFS文件路径对应的NameNode，分别向不同的NameNode获取Delegation Token：
static void obtainTokensForNamenodesInternal(Credentials credentials,
Path[] ps, Configuration conf) throws IOException {
//获取MR访问HDFS文件对应的所有NameNode文件系统
Set<FileSystem> fsSet = new HashSet<FileSystem>();
for(Path p: ps) {
fsSet.add(p.getFileSystem(conf));
}
//获取一个principal，标记为Delegation Token的renewer
String masterPrincipal = Master.getMasterPrincipal(conf);
for (FileSystem fs : fsSet) {
//在每个集群中，都创建Delegation Token
obtainTokensForNamenodesInternal(fs, credentials, conf, masterPrincipal);
}
}
getMasterPrincipal方法中，根据mapreduce.framework.name配置的值为yarn，选择使用yarn.resourcemanager.principal的值作为Delegation Token的renewer:
public static String getRmPrincipal(Configuration conf) throws IOException {
//返回yarn.resourcemanager.principal对应的值
String principal = conf.get(YarnConfiguration.RM_PRINCIPAL);
String prepared = null;
if (principal != null) {
prepared = getRmPrincipal(principal, conf);
}
return prepared;
}
如下，yarn.resourcemanager.principal配置一般为：
<property>
<name>yarn.resourcemanager.principal</name>
<value>hadoop/_HOST@NIE.NETEASE.COM</value>
</property>
随后，执行DistributedFileSystem.collectDelegationTokens方法。其中issuer就是当前DistributedFileSystem对象，renewer就是yarn.resourcemanager.principal的值，credentials暂时为空，tokens为空。
如果当前作业中没有指定集群的token，开始申请namenode创建token：
static void collectDelegationTokens(
final DelegationTokenIssuer issuer,
final String renewer,
final Credentials credentials,
final List<Token<?>> tokens) throws IOException {
//客户端访问的集群名
final String serviceName = issuer.getCanonicalServiceName();
// Collect token of the this issuer and then of its embedded children
if (serviceName != null) {
final Text service = new Text(serviceName);
//获取当前作业中指定集群名称的token
Token<?> token = credentials.getToken(service);
if (token == null) {
//如果当前作业中没有指定集群的token，开始申请namenode创建token
token = issuer.getDelegationToken(renewer);
if (token != null) {
tokens.add(token);
credentials.addToken(service, token);
}
}
}
//省略
}
4. NameNode创建DelegationToken
NameNode服务端执行FSNamesystem.getDelegationToken方法创建token。
- 先通过effectiveUser、realUser、renewer构建DelegationTokenIdentifier，DelegationTokenIdentifier会作为key检索对应的token，它本身不包含token信息。
- 创建token。
- 将创建token的行为记录成edits，持久化到磁盘中。
UserGroupInformation ugi = getRemoteUser();
//获取effectiveUser
String user = ugi.getUserName();
Text owner = new Text(user);
//获取realUser
Text realUser = null;
if (ugi.getRealUser() != null) {
realUser = new Text(ugi.getRealUser().getUserName());
}
//构建DelegationTokenIdentifier
DelegationTokenIdentifier dtId = new DelegationTokenIdentifier(owner,
renewer, realUser);
//创建DelegationToken
token = new Token<DelegationTokenIdentifier>(
dtId, dtSecretManager);
long expiryTime = dtSecretManager.getTokenExpiryTime(dtId);
//持久化edits
getEditLog().logGetDelegationToken(dtId, expiryTime);
4.1 构建DelegationTokenIdentifier
首先，观察构建DelegationTokenIdentifier的过程。在创建token前，namenode创建DelegationTokenIdentifier，当需要请求token时，namenode就会通过DelegationTokenIdentifier获取token信息。
注意，DelegationTokenIdentifier需要effectiveUser和realUser。当作业提交后，ResourceManager没有保存客户端的ugi信息，因此ResourceManager中，客户端用户没有kerberos权限访问其他组件。为了使作业正常执行，ResourceManager增加了代理功能，它使用自己的TGT认证其他Hadoop组件，认证信息中，effectiveUser表示ResourceManager自己的principal代表的user，realUser则是提交作业的user。如下IpcConnectionContextProtos.proto协议中定义了这两个User：
message UserInformationProto {
optional string effectiveUser = 1;
optional string realUser = 2;
}
注意，DelegationTokenIdentifier除了包含effectiveUser、realUser、renewer信息，还包含发行时间和最大时间，以及ID信息：
private Text owner;
private Text renewer;
private Text realUser;
private long issueDate;
private long maxDate;
private int sequenceNumber;
private int masterKeyId = 0;
4.2 创建Token
其次，NameNode根据DelegationTokenIdentifier构造token。它有以下重要成员：
- byte[] password：真正的token信息。
- identifier：用于检索token的key。
- kind：token类型。token有很多类型，例如RM_DELEGATION_TOKEN、HDFS_BLOCK_TOKEN、 TIMELINE_DELEGATION_TOKEN。此处NameNode创建的token类型是HDFS_DELEGATION_TOKEN。
public Token(T id, SecretManager<T> mgr) {
password = mgr.createPassword(id);
identifier = id.getBytes();
kind = id.getKind();
service = new Text();
}
NameNode通过DelegationTokenSecretManager.createPassword方法创建密码，这就是token的具体内容。
protected synchronized byte[] createPassword(TokenIdent identifier) {
int sequenceNum;
long now = Time.now();
//设置
sequenceNum = incrementDelegationTokenSeqNum();
identifier.setIssueDate(now);
identifier.setMaxDate(now + tokenMaxLifetime);
identifier.setMasterKeyId(currentKey.getKeyId());
identifier.setSequenceNumber(sequenceNum);
LOG.info("Creating password for identifier: " + formatTokenId(identifier)
+ ", currentKey: " + currentKey.getKeyId());
//创建遗传字节数组当成密码
byte[] password = createPassword(identifier.getBytes(), currentKey.getKey());
//创建包含renewDate、密码、trackingId等信息的DelegationTokenInformation
DelegationTokenInformation tokenInfo = new DelegationTokenInformation(now
+ tokenRenewInterval, password, getTrackingIdIfEnabled(identifier));
try {
//存储identifier和DelegationTokenInformation
storeToken(identifier, tokenInfo);
} catch (IOException ioe) {
LOG.error("Could not store token " + formatTokenId(identifier) + "!!",
ioe);
}
return password;
}
storeToken方法就将token对象放到NameNode对象中作为缓存，放入到currentTokens这个Map中。注意：storeNewToken方法为空，不执行任何操作：
protected final Map<TokenIdent, DelegationTokenInformation> currentTokens
= new ConcurrentHashMap<>();
protected void storeToken(TokenIdent ident,
DelegationTokenInformation tokenInfo) throws IOException {
currentTokens.put(ident, tokenInfo);
//NameNode中，storeNewToken方法为空，不执行
storeNewToken(ident, tokenInfo.getRenewDate());
}
另外，DelegationTokenSecretManager会启动ExpiredTokenRemover线程，定时清理过期token：
private void removeExpiredToken() throws IOException {
long now = Time.now();
Set<TokenIdent> expiredTokens = new HashSet<TokenIdent>();
synchronized (this) {
Iterator<Map.Entry<TokenIdent, DelegationTokenInformation>> i =
currentTokens.entrySet().iterator();
while (i.hasNext()) {
Map.Entry<TokenIdent, DelegationTokenInformation> entry = i.next();
long renewDate = entry.getValue().getRenewDate();
if (renewDate < now) {
expiredTokens.add(entry.getKey());
i.remove();
}
}
}
4.3 持久化Delegation Token
NameNode在创建完token后，会将DelegationTokenIdentifier写入到edits中：
getEditLog().logGetDelegationToken(dtId, expiryTime);
如下，调用FSEditLog.logGetDelegationToken方法，将DelegationTokenIdentifier保存在edits中：
void logGetDelegationToken(DelegationTokenIdentifier id,
long expiryTime) {
GetDelegationTokenOp op = GetDelegationTokenOp.getInstance(cache.get())
.setDelegationTokenIdentifier(id)
.setExpiryTime(expiryTime);
logEdit(op);
}
NamaNode不会将delegation token放入zk中，而是放入fsimage和edits中。在Standby NameNode加载了JournalNode的edits时，会初始化到fsimage文件中。Active NameNode从fsimage中恢复元数据时，会将DelegationTokenIdentifier信息通过createPassword方法恢复成为原有的tokens。 这就是NameNode中edits不保存token，只保存信息量更少的DelegationTokenIdentifier原因。
如下，NameNode和开始恢复元数据：
private void loadFSImage(StartupOption startOpt) throws IOException {
final FSImage fsImage = getFSImage();
//获取读取fsImage文件中的op操作，修改到内存中的fsimage中
final boolean staleImage
= fsImage.recoverTransitionRead(startOpt, this, recovery);
}
经过一系列的方法调用，会调用FSEditLogLoader.applyEditLogOp方法应用fsimage文件中的每一个op操作，它调用addPersistedDelegationToken开始恢复delegation token：
private long applyEditLogOp(FSEditLogOp op, FSDirectory fsDir,
StartupOption startOpt, int logVersion, long lastInodeId) throws IOException {
case OP_GET_DELEGATION_TOKEN: {
GetDelegationTokenOp getDelegationTokenOp
= (GetDelegationTokenOp)op;
fsNamesys.getDelegationTokenSecretManager()
.addPersistedDelegationToken(getDelegationTokenOp.token,
getDelegationTokenOp.expiryTime);
break;
}
}
可以看到，addPersistedDelegationToken方法根据DelegationTokenIdentifier直接产生token，放到currentTokens这个map中，这个token和持久化前的token一致。这样，就算NameNode切换，新NameNode启动时，delegation token依然存在，内容不变：
public synchronized void addPersistedDelegationToken(
DelegationTokenIdentifier identifier, long expiryTime) throws IOException {
if (running) {
// a safety check
throw new IOException(
"Can't add persisted delegation token to a running SecretManager.");
}
int keyId = identifier.getMasterKeyId();
DelegationKey dKey = allKeys.get(keyId);
if (dKey == null) {
LOG
.warn("No KEY found for persisted identifier "
+ identifier.toString());
return;
}
//直接创建token，放到内存中
byte[] password = createPassword(identifier.getBytes(), dKey.getKey());
if (identifier.getSequenceNumber() > this.delegationTokenSequenceNumber) {
this.delegationTokenSequenceNumber = identifier.getSequenceNumber();
}
if (currentTokens.get(identifier) == null) {
currentTokens.put(identifier, new DelegationTokenInformation(expiryTime,
password, getTrackingIdIfEnabled(identifier)));
} else {
throw new IOException(
"Same delegation token being added twice; invalid entry in fsimage or editlogs");
}
}
5. Yarn客户端将Delegation Token传输给ResourceMananger
客户端中，YARNRunner.submitJob提交作业，它会先将申请到的namenode delegation token放入到ApplicationSubmissionContext中，再提交作业：
public JobStatus submitJob(JobID jobId, String jobSubmitDir, Credentials ts)
throws IOException, InterruptedException {
addHistoryToken(ts);
//将 delegation token放入到ApplicationSubmissionContext中，注意Credentials中保存的就是token信息
ApplicationSubmissionContext appContext =
createApplicationSubmissionContext(conf, jobSubmitDir, ts);
// Submit to ResourceManager
try {
ApplicationId applicationId =
resMgrDelegate.submitApplication(appContext);
//省略
}
createApplicationSubmissionContext创建作业启动上下文，token信息已经放到了AM启动的上下文中：
public ApplicationSubmissionContext createApplicationSubmissionContext(
Configuration jobConf, String jobSubmitDir, Credentials ts)
throws IOException {
ApplicationId applicationId = resMgrDelegate.getApplicationId();
// Setup LocalResources
Map<String, LocalResource> localResources =
setupLocalResources(jobConf, jobSubmitDir);
// Setup security tokens
DataOutputBuffer dob = new DataOutputBuffer();
ts.writeTokenStorageToStream(dob);
//获取token信息
ByteBuffer securityTokens =
ByteBuffer.wrap(dob.getData(), 0, dob.getLength());
//将token信息放入
// Setup ContainerLaunchContext for AM container
List<String> vargs = setupAMCommand(jobConf);
//token放入到AM启动的上下文中
ContainerLaunchContext amContainer = setupContainerLaunchContextForAM(
jobConf, localResources, securityTokens, vargs);
appContext.setAMContainerSpec(amContainer); // AM Container
//省略
}
6. ResourceManager启动container时携带delegation token信息
ResourceManager接收到客户端的tokens，调用AMLauncher.launch准备启动AppMaster的container，将客户端的tokens信息放到NodeMananger的请求中，这样NodeManager就有tokens信息，可以根据该tokens信息访问HDFS了：
private void launch() throws IOException, YarnException {
connect();
ContainerId masterContainerID = masterContainer.getId();
//获取客户端提交时的Context，里面包含tokens
ApplicationSubmissionContext applicationContext =
application.getSubmissionContext();
LOG.info("Setting up container " + masterContainer
+ " for AM " + application.getAppAttemptId());
//创建AM启动相关Context，里面携带tokens
ContainerLaunchContext launchContext =
createAMContainerLaunchContext(applicationContext, masterContainerID);
//将Context发送给NodeMananger，准备启动container
StartContainersResponse response =
containerMgrProxy.startContainers(allRequests);
if (response.getFailedRequests() != null
&& response.getFailedRequests().containsKey(masterContainerID)) {
Throwable t =
response.getFailedRequests().get(masterContainerID).deSerialize();
parseAndThrowException(t);
} else {
LOG.info("Done launching container " + masterContainer + " for AM "
+ application.getAppAttemptId());
}
}
7. ResourceManager定时更新tokens
每次RM接收到handleAppSubmitEvent请求后，都会执行DelegationTokenRenewer.handleAppSubmitEvent方法开始更新delegation token。如下所示，DelegationTokenRenewer保存app→DelegationTokenToRenew映射，也保存token→DelegationTokenToRenew的映射。
handleAppSubmitEvent为每个token创建DelegationTokenToRenew对象，并为每个token设置定时任务更新token：
private ConcurrentMap<ApplicationId, Set<DelegationTokenToRenew>> appTokens =
new ConcurrentHashMap<ApplicationId, Set<DelegationTokenToRenew>>();
private ConcurrentMap<Token<?>, DelegationTokenToRenew> allTokens =
new ConcurrentHashMap<Token<?>, DelegationTokenToRenew>();
private void handleAppSubmitEvent(AbstractDelegationTokenRenewerAppEvent evt)
throws IOException, InterruptedException {
ApplicationId applicationId = evt.getApplicationId();
//获取客户端传送过来的tokens
Credentials ts = evt.getCredentials();
//遍历客户端传递过来的所有token
for (Token<?> token : tokens) {
//如果客户端
DelegationTokenToRenew dttr = allTokens.get(token);
if (dttr == null) {
//如果不存在DelegationTokenToRenew对象，为该token创建一个对象
dttr = new DelegationTokenToRenew(Arrays.asList(applicationId), token,
tokenConf, now, shouldCancelAtEnd, evt.getUser());
try {
//尝试更新一次token，并更新token下次的过期时间。由于这是token的第一个DelegationTokenToRenew，直接更新即可，不需要剔除旧的token。
renewToken(dttr);
//省略
for (DelegationTokenToRenew dtr : tokenList) {
//将DelegationTokenToRenew放入allTokens这个Map中
//可见allTokens用于记录token有没有启动定时任务
DelegationTokenToRenew currentDtr =
allTokens.putIfAbsent(dtr.token, dtr);
//设置定时任务启动token更新流程
setTimerForTokenRenewal(dtr);
}
}
}
}
setTimerForTokenRenewal启动线程定时更新token：
protected void setTimerForTokenRenewal(DelegationTokenToRenew token)
throws IOException {
// calculate timer time
long expiresIn = token.expirationDate - System.currentTimeMillis();
if (expiresIn <= 0) {
LOG.info("Will not renew token " + token);
return;
}
long renewIn = token.expirationDate - expiresIn/10; // little bit before the expiration
// need to create new task every time
RenewalTimerTask tTask = new RenewalTimerTask(token);
token.setTimerTask(tTask); // keep reference to the timer
renewalTimer.schedule(token.timerTask, new Date(renewIn));
LOG.info("Renew " + token + " in " + expiresIn + " ms, appId = "
+ token.referringAppIds);
}
9. RM无法更新长期运行的container的delegation token问题
在ResourceManager中，会为每个app创建DelegationTokenToRenew，并启动定时更新任务。这样，一旦要启动新的container，就会将最新的delegation token发送给container。这里有一个漏洞，token有效期为7天，更新时间为1天，如果container运行了7天以上，那么token过期，这时resourcemanager不会将最新的delegation token传给container，因此Yarn作业会失败。
对于Mapreduce批处理作业，每个作业一般每天定时执行一次，一天内就可以完成批处理作业。但是对于spark streaming或者flink这种长时间运行的应用而言，它们的应用程序会运行超过7天。
Spark和Flink为了解决这个问题，将keytab上传到HDFS中，Spark AppMaster定期通过keytab进行认证获取ticket，再访问NameNode获取token，再将token持久化写到HDFS中，container再从HDFS下载token文件即可完成token更新。
首先，spark提交作业时，设置了两个参数"--keytab"和"--principal”，将keytab放在HDFS中，并设置AppMaster的环境，其中，spark.yarn.credentials.file表示要存储token的位置：
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)
}
...
}
在AppMaster执行过程中，定期重新认证kerberos，并重新刷新token，将token上传到spark.yarn.credentials.file路径中。在writeNewTokensToHDFS方法中进行：
private def writeNewTokensToHDFS(principal: String, keytab: String): Unit = {
logInfo(s"Attempting to login to KDC using principal: $principal")
//1）重新登录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）使用新的登录身份信息向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)将新获取的token添加到当前登录用户中
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）将credentials信息写到目标文件中
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
}
Executor定期从spark.yarn.credentials.file路径中获取token文件：
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)
}
注意：如果AppMaster中没有创建app对应的DelegationTokenToRenew，就有RM创建并定时启动token更新逻辑；如果AppMaster创建app对应的DelegationTokenToRenew了，那么RM就不会创建并定时更新token。
10. Delegation Token认证框架
通过https://blog.51cto.com/u_15327484/8153877文章可以看到，Hadoop在认证时，使用SASL框架。当申请好token后，就会使用DIGEST-MD5认证方式进行认证：
public enum AuthMethod {
SIMPLE((byte) 80, ""),
KERBEROS((byte) 81, "GSSAPI"),
@Deprecated
DIGEST((byte) 82, "DIGEST-MD5"),
TOKEN((byte) 82, "DIGEST-MD5"),
PLAIN((byte) 83, "PLAIN");
}
在执行rpc请求前，会执行SaslClient.evaluateChallenge进行认证。此时它使用的是DigestMD5Client.evaluateChallenge进行认证：
改认证方式不会再访问TGS获取service ticket，直接向服务端请求认证，详细过程省略。
