1. 概要
前面介紹了如何把Drill部署在YARN上，然後通過Drill-on-YARN用戶端，你可以啟動、停止、調整、清零指令操作Drill。但是在這麼指令背後，到底是如何執行的呢，下面會對Drill-on-YARN的源碼進行詳細的解析，重點解析啟動過程，其他指令簡單介紹。
說明：下面涉及到的代碼，以drill 1.14.0為準，并且為了減少篇幅，進行了删減。
2. Drill-on-YARN start
2.1 drill-on-yarn.sh
通過檢視drill-on-yarn.sh腳本，很容易發現最終執行的java類是
CLIENT_CMD="$JAVA $VM_OPTS -cp $CP org.apache.drill.yarn.client.DrillOnYarn ${args[@]}"
。
org.apache.drill.yarn.client.DrillOnYarn
便是啟動Drill-on-YARN的入口。我們可以總覽一下這個類：
public class DrillOnYarn {
public static void main(String argv[]) {
BasicConfigurator.configure();
ClientContext.init();
run(argv);
}
public static void run(String argv[]) {
ClientContext context = ClientContext.instance();
CommandLineOptions opts = new CommandLineOptions();
if (!opts.parse(argv)) {
opts.usage();
context.exit(-1);
}
if (opts.getCommand() == null) {
opts.usage();
context.exit(-1);
}
try {
DrillOnYarnConfig.load().setClientPaths();
} catch (DoyConfigException e) {
ClientContext.err.println(e.getMessage());
context.exit(-1);
}
ClientCommand cmd;
switch (opts.getCommand()) {
case UPLOAD:
cmd = new StartCommand(true, false);
break;
case START:
cmd = new StartCommand(true, true);
break;
case DESCRIBE:
cmd = new PrintConfigCommand();
break;
case STATUS:
cmd = new StatusCommand();
break;
case STOP:
cmd = new StopCommand();
break;
case CLEAN:
cmd = new CleanCommand();
break;
case RESIZE:
cmd = new ResizeCommand();
break;
default:
cmd = new HelpCommand();
}
cmd.setOpts(opts);
try {
cmd.run();
} catch (ClientException e) {
displayError(opts, e);
context.exit(1);
}
}
} 可以看到入口main方法，其中最關鍵的便是run方法，包含了很多的指令，我們重點看start指令，代碼如下：
public void run() throws ClientException {
checkExistingApp();
dryRun = opts.dryRun;
config = DrillOnYarnConfig.config();
FileUploader uploader = upload();
if (launch) {
launch(uploader);
}
} 概括的來說，它主要包含以下流程：
- 檢查application是否已經存在，如果已經存在，便不允許啟動，否則執行啟動操作（此處檢查的application是YARN的application，啟動成功會将YARN的applicationId寫入本地磁盤的一個檔案，通過此檔案來檢查）。
- 上傳Drill二方包和site目錄下的内容至DFS上，其中site目錄下的内容會被打包為site.tar.gz
public void run() throws ClientException { setup(); uploadDrillArchive(); if (hasSiteDir()) { uploadSite(); } } - 啟動ApplicationMaster，主要流程為：
- 建立YARN用戶端，并啟動
// AMRunner#connectToYarn private void connectToYarn() { System.out.print("Loading YARN Config..."); client = new YarnRMClient(); System.out.println(" Loaded."); } - 建立ApplicationMaster
// AMRunner#createApp private void createApp() throws ClientException { try { appResponse = client.createAppMaster(); } catch (YarnClientException e) { throw new ClientException("Failed to allocate Drill application master", e); } appId = appResponse.getApplicationId(); System.out.println("Application ID: " + appId.toString()); } - 設定ApplicationMaster上下文，包括：Heap memory、Class Path、啟動的指令（dirll-am.sh）、啟動am容器使用的資源（memory、vCores、disks）
- 校驗資源，主要是ApplicationMaster使用資源是否超過了YARN的設定
- 送出ApplicationMaster
private void launchApp(AppSpec master) throws ClientException { try { client.submitAppMaster(master); } catch (YarnClientException e) { throw new ClientException("Failed to start Drill application master", e); } } - 等待啟動，并列印啟動日志
- 将ApplicationMaster的appid寫入檔案（在第1步，檢測Application是否存在，就是使用這個檔案）
- 建立YARN用戶端，并啟動
ApplicationMaster啟動後，會向RM申請資源，啟動Drillbits，下面詳細介紹ApplicationMaster啟動後的操作
2.2 drill-am.sh
通過檢視drill-am.sh腳本，很容易發現最終執行的java類是
AMCMD="$JAVA $AM_JAVA_OPTS ${args[@]} -cp $CP org.apache.drill.yarn.appMaster.DrillApplicationMaster"
org.apache.drill.yarn.appMaster.DrillApplicationMaste
表示ApplicationMaster執行的入口，下面總覽一下這個類：
public class DrillApplicationMaster {
public static void main(String[] args) {
LOG.trace("Drill Application Master starting.");
try {
DrillOnYarnConfig.load().setAmDrillHome();
} catch (DoyConfigException e) {
System.err.println(e.getMessage());
System.exit(-1);
}
Dispatcher dispatcher;
try {
dispatcher = (new DrillControllerFactory()).build();
} catch (ControllerFactoryException e) {
LOG.error("Setup failed, exiting: " + e.getMessage(), e);
System.exit(-1);
return;
}
try {
if (!dispatcher.start()) {
return;
}
} catch (Throwable e) {
LOG.error("Fatal error, exiting: " + e.getMessage(), e);
System.exit(-1);
}
WebServer webServer = new WebServer(dispatcher);
try {
webServer.start();
} catch (Exception e) {
LOG.error("Web server setup failed, exiting: " + e.getMessage(), e);
System.exit(-1);
}
try {
dispatcher.run();
} catch (Throwable e) {
LOG.error("Fatal error, exiting: " + e.getMessage(), e);
System.exit(-1);
} finally {
try {
webServer.close();
} catch (Exception e) {
}
}
}
} 概況的來說，它主要包含以下流程：
- 加載Drill-on-YARN的配置，并設定AM的DirllHome，比如
/home/admin/tmp2/hadoop/nm-local-dir/usercache/admin/appcache/application_1534698866098_0022/container_1534698866098_0022_01_000001/drill/apache-drill-1.14.0
- 構造Dispatcher，Dispatcher用于配置設定YARN、timer、ZooKeeper事件給給叢集控制器，它是輕量級多線程的，用于響應RM、NM、timer線程的事件，對于某一個事件，它是連續的，是以需要同步，但是不同類型的事件不需要同步。整個的構造流程如下：
- 準備資源，包括：drill二方包、site壓縮包的目錄
private Map<String, LocalResource> prepareResources() { ... drillArchivePath = drillConfig.getDrillArchiveDfsPath(); siteArchivePath = drillConfig.getSiteArchiveDfsPath(); ... } - 定義任務啟動的規格（TaskSpec），包括：運作時環境、YARN container的規格、dirllbit的規格
private TaskSpec buildDrillTaskSpec(Map<String, LocalResource> resources) throws DoyConfigException { ... ContainerRequestSpec containerSpec = new ContainerRequestSpec(); containerSpec.memoryMb = config.getInt(DrillOnYarnConfig.DRILLBIT_MEMORY); ... LaunchSpec drillbitSpec = new LaunchSpec(); ... TaskSpec taskSpec = new TaskSpec(); taskSpec.name = "Drillbit"; taskSpec.containerSpec = containerSpec; taskSpec.launchSpec = drillbitSpec; } - 設定Dispatcher的控制器：實作類為ClusterControllerImpl，它主要通過狀态來控制Drill叢集、調整整個叢集的任務（Drill啟動、停止等任務）、處理container的回調
public void setYarn(AMYarnFacade yarn) throws YarnFacadeException { this.yarn = yarn; controller = new ClusterControllerImpl(yarn); } - 為控制器注冊Scheduler，比如DrillbitScheduler，此外Scheduler配置來源于之前drill-on-yarn.conf
cluster: [ { name: "drill-group1" type: "basic" count: 1 } ]... ClusterDef.ClusterGroup pool = ClusterDef.getCluster(config, 0); Scheduler testGroup = new DrillbitScheduler(pool.getName(), taskSpec, pool.getCount(), requestTimeoutSecs, maxExtraNodes); dispatcher.getController().registerScheduler(testGroup); ... - 建立ZooKeeper叢集協調器
String zkConnect = config.getString(DrillOnYarnConfig.ZK_CONNECT); String zkRoot = config.getString(DrillOnYarnConfig.ZK_ROOT); String clusterId = config.getString(DrillOnYarnConfig.CLUSTER_ID);
- 準備資源，包括：drill二方包、site壓縮包的目錄
- 啟動Dispatcher，主要啟動AMRMClientAsync、NMClientAsync、YarnClient
... yarn.start(new ResourceCallback(), new NodeCallback()); String url = trackingUrl.replace("<port>", Integer.toString(httpPort)); if (DrillOnYarnConfig.config().getBoolean(DrillOnYarnConfig.HTTP_ENABLE_SSL)) { url = url.replace("http:", "https:"); } yarn.register(url); controller.started(); ...... resourceMgr = AMRMClientAsync.createAMRMClientAsync(pollPeriodMs, resourceCallback); resourceMgr.init(conf); resourceMgr.start(); ... nodeMgr = NMClientAsync.createNMClientAsync(nodeCallback); nodeMgr.init(conf); nodeMgr.start(); ... client = YarnClient.createYarnClient(); client.init(conf); client.start(); ... - 啟動dirll運維界面
WebServer webServer = new WebServer(dispatcher); webServer.start(); - 運作Dispatcher，主要是啟動一個線程，此線程會不斷的輪詢目前的任務隊列中的任務情況，比如啟動、停止、resize等類型的任務，然後執行相應的動作，拿啟動來說
- 添加一個啟動任務，然後放入pendingTask隊列中
if (state == State.LIVE) { adjustTasks(curTime); requestContainers(); } - 向RM請求container：建立一個ContainerRequest
ContainerRequest request = containerSpec.makeRequest(); resourceMgr.addContainerRequest(containerSpec.makeRequest()); return request; - ResourceCallback監聽container配置設定，然後啟動container
private class ResourceCallback implements AMRMClientAsync.CallbackHandler { @Override public void onContainersAllocated(List<Container> containers) { controller.containersAllocated(containers); } }public void containerAllocated(EventContext context, Container container) { Task task = context.task; LOG.info(task.getLabel() + " - Received container: " + DoYUtil.describeContainer(container)); context.group.dequeueAllocatingTask(task); // No matter what happens below, we don't want to ask for this // container again. The RM async API is a bit bizarre in this // regard: it will keep asking for container over and over until // we tell it to stop. context.yarn.removeContainerRequest(task.containerRequest); // The container is need both in the normal and in the cancellation // path, so set it here. task.container = container; if (task.cancelled) { context.yarn.releaseContainer(container); taskStartFailed(context, Disposition.CANCELLED); return; } task.error = null; task.completionStatus = null; transition(context, LAUNCHING); // The pool that manages this task wants to know that we have // a container. The task manager may want to do some task- // specific setup. context.group.containerAllocated(context.task); context.getTaskManager().allocated(context); // Go ahead and launch a task in the container using the launch // specification provided by the task group (pool). try { context.yarn.launchContainer(container, task.getLaunchSpec()); task.launchTime = System.currentTimeMillis(); } catch (YarnFacadeException e) { LOG.error("Container launch failed: " + task.getContainerId(), e); // This may not be the right response. RM may still think // we have the container if the above is a local failure. task.error = e; context.group.containerReleased(task); task.container = null; taskStartFailed(context, Disposition.LAUNCH_FAILED); } } - NodeCallback監聽container啟動
public class NodeCallback implements NMClientAsync.CallbackHandler { @Override public void onStartContainerError(ContainerId containerId, Throwable t) { controller.taskStartFailed(containerId, t); } @Override public void onContainerStarted(ContainerId containerId, Map<String, ByteBuffer> allServiceResponse) { controller.containerStarted(containerId); } @Override public void onContainerStatusReceived(ContainerId containerId, ContainerStatus containerStatus) { } @Override public void onGetContainerStatusError(ContainerId containerId, Throwable t) { } @Override public void onStopContainerError(ContainerId containerId, Throwable t) { controller.stopTaskFailed(containerId, t); } @Override public void onContainerStopped(ContainerId containerId) { controller.containerStopped(containerId); } }
- 添加一個啟動任務，然後放入pendingTask隊列中
2.3 fail over
Drill-on-YARN除了提供start、stop、resize功能外，還提供了fail over功能，目前某個drillbit挂掉後，Drill-on-YARN會嘗試再次啟動drillbit，目前重試的次數為2。此外，如果一個drillbit所在的節點頻繁挂掉，會被列入黑名單。
我們可以通過手動kill drillbit來模拟drillbit挂掉的情況，然後等待一會兒，可以看到，drillbit程序重新啟動了。下面我們看看，代碼的執行流程
- drillbit挂掉，container結束
private class ResourceCallback implements AMRMClientAsync.CallbackHandler {
@Override
public void onContainersCompleted(List<ContainerStatus> statuses) {
controller.containersCompleted(statuses);
}
} - retry task：重新将這個task加入pendingTasks，然後輪詢的線程檢測到pendingTasks不為空，執行啟動操作
protected void taskTerminated(EventContext context) {
Task task = context.task;
context.getTaskManager().completed(context);
context.group.containerReleased(task);
assert task.completionStatus != null;
// container結束的狀态不是0，說明不是正常結束
if (task.completionStatus.getExitStatus() == 0) {
taskEnded(context, Disposition.COMPLETED);
context.group.taskEnded(context.task);
} else {
taskEnded(context, Disposition.RUN_FAILED);
retryTask(context);
}
} private void retryTask(EventContext context) {
Task task = context.task;
assert task.state == END;
if (!context.controller.isLive() || !task.retryable()) {
context.group.taskEnded(task);
return;
}
if (task.tryCount > task.taskGroup.getMaxRetries()) {
LOG.error(task.getLabel() + " - Too many retries: " + task.tryCount);
task.disposition = Disposition.TOO_MANY_RETRIES;
context.group.taskEnded(task);
return;
}
LOG.info(task.getLabel() + " - Retrying task, try " + task.tryCount);
context.group.taskRetried(task);
task.reset();
transition(context, START);
context.group.enqueuePendingRequest(task);
} 3. 停止
除了前面詳情介紹的start指令外，Drill-on-YARN也提供了stop指令，其中stop分兩種：
- 強制停止：直接調用yarn用戶端的killApplication api
yarnClient.killApplication(appId);
- 優雅停止：先清理所有的任務，包括pending、running的，然後調用yarn的api殺死容器，關閉controller，然後通知am運作結束
...
for (Task task : getStartingTasks()) {
context.setTask(task);
context.getState().cancel(context);
}
for (Task task : getActiveTasks()) {
context.setTask(task);
context.getState().cancel(context);
}
... ...
context.yarn.killContainer(task.container);
... public void run() throws YarnFacadeException {
...
boolean success = controller.waitForCompletion();
...
...
finish(success, null);
...
} public boolean waitForCompletion() {
start();
synchronized (completionMutex) {
try {
completionMutex.wait();
} catch (InterruptedException e) {
}
}
return succeeded();
} public void finish(boolean succeeded, String msg) throws YarnFacadeException {
nodeMgr.stop();
String appMsg = "Drill Cluster Shut-Down";
FinalApplicationStatus status = FinalApplicationStatus.SUCCEEDED;
if (!succeeded) {
appMsg = "Drill Cluster Fatal Error - check logs";
status = FinalApplicationStatus.FAILED;
}
if (msg != null) {
appMsg = msg;
}
try {
resourceMgr.unregisterApplicationMaster(status, appMsg, "");
} catch (YarnException | IOException e) {
throw new YarnFacadeException("Deregister AM failed", e);
}
resourceMgr.stop();
} 4. resize
resize流程為：調整quantity（保留多少個container），之後輪詢線程會根據quantity，調整任務，執行resize操作
public int resize(int level) {
int limit = quantity + state.getController().getFreeNodeCount() +maxExtraNodes;
return super.resize( Math.min( limit, level ) );
} 5. 總結
總的來說，Drill-on-YARN分為兩大子產品，drill-on-yarn.sh和drill-am.sh。drill-on-yarn.sh用于啟動ApplicationMaster，drill-am.sh用于向ResourceManager申請資源并啟動Drill叢集。其中Drill的啟動、停止、縮容、擴容，都被封裝為一個任務，在執行這些指令時，會建構一個任務，放入任務隊列中。有一個線程會一直輪詢此隊列，根據隊列中的任務執行不同的操作，進而達到啟動、停止、縮容、擴容Drill叢集的功能。此外，相比獨立部署，Drill-on-YARN提供的failover功能強化了Drill的穩定性。
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