HADOOP-16524. Automatic keystore reloading for HttpServer2

Reapply of issue reverted first because it caused yarn failures and
then again because the commit message was incorrectly formatted.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/HttpServer2.java

@@ -27,14 +27,17 @@
 import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
-import java.util.Arrays;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.Enumeration;
-import java.util.HashMap;
+import java.nio.file.Paths;
 import java.util.List;
+import java.util.ArrayList;
 import java.util.Map;
+import java.util.HashMap;
+import java.util.Collections;
+import java.util.Optional;
 import java.util.Properties;
+import java.util.Enumeration;
+import java.util.Arrays;
+import java.util.Timer;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -75,6 +78,8 @@
 import org.apache.hadoop.security.authentication.server.PseudoAuthenticationHandler;
 import org.apache.hadoop.security.authentication.util.SignerSecretProvider;
 import org.apache.hadoop.security.authorize.AccessControlList;
+import org.apache.hadoop.security.ssl.FileBasedKeyStoresFactory;
+import org.apache.hadoop.security.ssl.FileMonitoringTimerTask;
 import org.apache.hadoop.security.ssl.SSLFactory;
 import org.apache.hadoop.util.ReflectionUtils;
 import org.apache.hadoop.util.Shell;
@@ -186,6 +191,7 @@ public final class HttpServer2 implements FilterContainer {
   static final String STATE_DESCRIPTION_ALIVE = " - alive";
   static final String STATE_DESCRIPTION_NOT_LIVE = " - not live";
   private final SignerSecretProvider secretProvider;
+  private final Optional<java.util.Timer> configurationChangeMonitor;
   private XFrameOption xFrameOption;
   private boolean xFrameOptionIsEnabled;
   public static final String HTTP_HEADER_PREFIX = "hadoop.http.header.";
@@ -244,6 +250,8 @@ public static class Builder {
 
     private boolean sniHostCheckEnabled;
 
+    private Optional<Timer> configurationChangeMonitor = Optional.empty();
+
     public Builder setName(String name){
       this.name = name;
       return this;
@@ -574,12 +582,45 @@ private ServerConnector createHttpsChannelConnector(
       }
 
       setEnabledProtocols(sslContextFactory);
+
+      long storesReloadInterval =
+          conf.getLong(FileBasedKeyStoresFactory.SSL_STORES_RELOAD_INTERVAL_TPL_KEY,
+              FileBasedKeyStoresFactory.DEFAULT_SSL_STORES_RELOAD_INTERVAL);
+
+      if (storesReloadInterval > 0) {
+        this.configurationChangeMonitor = Optional.of(
+            this.makeConfigurationChangeMonitor(storesReloadInterval, sslContextFactory));
+      }
+
       conn.addFirstConnectionFactory(new SslConnectionFactory(sslContextFactory,
           HttpVersion.HTTP_1_1.asString()));
 
       return conn;
     }
 
+    private Timer makeConfigurationChangeMonitor(long reloadInterval,
+        SslContextFactory.Server sslContextFactory) {
+      java.util.Timer timer = new java.util.Timer(FileBasedKeyStoresFactory.SSL_MONITORING_THREAD_NAME, true);
+      //
+      // The Jetty SSLContextFactory provides a 'reload' method which will reload both
+      // truststore and keystore certificates.
+      //
+      timer.schedule(new FileMonitoringTimerTask(
+              Paths.get(keyStore),
+              path -> {
+                LOG.info("Reloading certificates from store keystore " + keyStore);
+                try {
+                  sslContextFactory.reload(factory -> { });
+                } catch (Exception ex) {
+                  LOG.error("Failed to reload SSL keystore certificates", ex);
+                }
+              },null),
+          reloadInterval,
+          reloadInterval
+      );
+      return timer;
+    }
+
     private void setEnabledProtocols(SslContextFactory sslContextFactory) {
       String enabledProtocols = conf.get(SSLFactory.SSL_ENABLED_PROTOCOLS_KEY,
           SSLFactory.SSL_ENABLED_PROTOCOLS_DEFAULT);
@@ -622,6 +663,7 @@ private HttpServer2(final Builder b) throws IOException {
     this.webAppContext = createWebAppContext(b, adminsAcl, appDir);
     this.xFrameOptionIsEnabled = b.xFrameEnabled;
     this.xFrameOption = b.xFrameOption;
+    this.configurationChangeMonitor = b.configurationChangeMonitor;
 
     try {
       this.secretProvider =
@@ -1420,6 +1462,16 @@ void openListeners() throws Exception {
    */
   public void stop() throws Exception {
     MultiException exception = null;
+    if (this.configurationChangeMonitor.isPresent()) {
+      try {
+        this.configurationChangeMonitor.get().cancel();
+      } catch (Exception e) {
+        LOG.error(
+            "Error while canceling configuration monitoring timer for webapp"
+                + webAppContext.getDisplayName(), e);
+        exception = addMultiException(exception, e);
+      }
+    }
     for (ServerConnector c : listeners) {
       try {
         c.close();