YARN-8559. Expose mutable-conf scheduler's configuration in RM /scheduler-conf endpoint. Contributed by Weiwei Yang.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/MutableConfigurationProvider.java

@@ -18,6 +18,7 @@
 
 package org.apache.hadoop.yarn.server.resourcemanager.scheduler;
 
+import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.yarn.webapp.dao.SchedConfUpdateInfo;
 
@@ -58,6 +59,12 @@ public interface MutableConfigurationProvider {
    */
   void confirmPendingMutation(boolean isValid) throws Exception;
 
+  /**
+   * Returns scheduler configuration cached in this provider.
+   * @return scheduler configuration.
+   */
+  Configuration getConfiguration();
+
   /**
    * Closes the configuration provider, releasing any required resources.
    * @throws IOException on failure to close

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/conf/MutableCSConfigurationProvider.java

@@ -122,6 +122,11 @@ public class MutableCSConfigurationProvider implements CSConfigurationProvider,
     return new CapacitySchedulerConfiguration(loadedConf, false);
   }
 
+  @Override
+  public Configuration getConfiguration() {
+    return new Configuration(schedConf);
+  }
+
   @Override
   public ConfigurationMutationACLPolicy getAclMutationPolicy() {
     return aclMutationPolicy;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/RMWebServices.java

@@ -188,6 +188,7 @@ import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ResourceInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.SchedulerInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.SchedulerTypeInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.StatisticsItemInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ConfInfo;
 import org.apache.hadoop.yarn.server.security.ApplicationACLsManager;
 import org.apache.hadoop.yarn.server.utils.BuilderUtils;
 import org.apache.hadoop.yarn.server.webapp.WebServices;
@@ -2531,4 +2532,44 @@ public class RMWebServices extends WebServices implements RMWebServiceProtocol {
           .build();
     }
   }
+
+  @GET
+  @Path("/scheduler-conf")
+  @Produces({ MediaType.APPLICATION_JSON + "; " + JettyUtils.UTF_8,
+      MediaType.APPLICATION_XML + "; " + JettyUtils.UTF_8 })
+  public Response getSchedulerConfiguration(@Context HttpServletRequest hsr)
+      throws AuthorizationException {
+    init();
+    // Only admin user is allowed to read scheduler conf,
+    // in order to avoid leaking sensitive info, such as ACLs
+    UserGroupInformation callerUGI = getCallerUserGroupInformation(hsr, true);
+    ApplicationACLsManager aclsManager = rm.getApplicationACLsManager();
+    if (aclsManager.areACLsEnabled()) {
+      if (callerUGI == null || !aclsManager.isAdmin(callerUGI)) {
+        String msg = "Only admins can carry out this operation.";
+        throw new ForbiddenException(msg);
+      }
+    }
+
+    ResourceScheduler scheduler = rm.getResourceScheduler();
+    if (scheduler instanceof MutableConfScheduler
+        && ((MutableConfScheduler) scheduler).isConfigurationMutable()) {
+      MutableConfigurationProvider mutableConfigurationProvider =
+          ((MutableConfScheduler) scheduler).getMutableConfProvider();
+      // We load the cached configuration from configuration store,
+      // this should be the conf properties used by the scheduler.
+      Configuration schedulerConf = mutableConfigurationProvider
+          .getConfiguration();
+      return Response.status(Status.OK)
+          .entity(new ConfInfo(schedulerConf))
+          .build();
+    } else {
+      return Response.status(Status.BAD_REQUEST).entity(
+          "This API only supports to retrieve scheduler configuration"
+              + " from a mutable-conf scheduler, underneath scheduler "
+              + scheduler.getClass().getSimpleName()
+              + " is not an instance of MutableConfScheduler")
+          .build();
+    }
+  }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/dao/ConfInfo.java

@@ -0,0 +1,72 @@
+/**
+ * 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.hadoop.yarn.server.resourcemanager.webapp.dao;
+
+import org.apache.hadoop.conf.Configuration;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.XmlRootElement;
+import java.util.ArrayList;
+
+@XmlRootElement(name = "configuration")
+@XmlAccessorType(XmlAccessType.FIELD)
+public class ConfInfo {
+
+  protected ArrayList<ConfItem> property = new ArrayList<>();
+
+  public ConfInfo() {
+  } // JAXB needs this
+
+  public ConfInfo(Configuration conf) {
+    conf.forEach(entry ->
+        add(new ConfItem(entry.getKey(), entry.getValue())));
+  }
+
+  public void add(ConfItem confItem) {
+    property.add(confItem);
+  }
+
+  public ArrayList<ConfItem> getItems() {
+    return property;
+  }
+
+  @XmlAccessorType(XmlAccessType.FIELD)
+  public static class ConfItem {
+
+    private String name;
+    private String value;
+
+    public ConfItem() {
+      // JAXB needs this
+    }
+
+    public ConfItem(String name, String value){
+      this.name = name;
+      this.value = value;
+    }
+
+    public String getKey() {
+      return name;
+    }
+
+    public String getValue() {
+      return value;
+    }
+  }
+}

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/TestRMWebServicesConfigurationMutation.java

@@ -39,6 +39,9 @@ import org.apache.hadoop.yarn.webapp.JerseyTestBase;
 import org.apache.hadoop.yarn.webapp.dao.QueueConfigInfo;
 import org.apache.hadoop.yarn.webapp.dao.SchedConfUpdateInfo;
 import org.apache.hadoop.yarn.webapp.util.YarnWebServiceUtils;
+import org.codehaus.jettison.json.JSONArray;
+import org.codehaus.jettison.json.JSONException;
+import org.codehaus.jettison.json.JSONObject;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -54,6 +57,7 @@ import java.util.Map;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertNotNull;
 
 /**
  * Test scheduler configuration mutation via REST API.
@@ -153,8 +157,40 @@ public class TestRMWebServicesConfigurationMutation extends JerseyTestBase {
         .contextPath("jersey-guice-filter").servletPath("/").build());
   }
 
+  private CapacitySchedulerConfiguration getSchedulerConf()
+      throws JSONException {
+    WebResource r = resource();
+    ClientResponse response =
+        r.path("ws").path("v1").path("cluster")
+            .queryParam("user.name", userName).path("scheduler-conf")
+            .accept(MediaType.APPLICATION_JSON)
+            .get(ClientResponse.class);
+    assertEquals(Status.OK.getStatusCode(), response.getStatus());
+    JSONObject json = response.getEntity(JSONObject.class);
+    JSONArray items = (JSONArray) json.get("property");
+    CapacitySchedulerConfiguration parsedConf =
+        new CapacitySchedulerConfiguration();
+    for (int i=0; i<items.length(); i++) {
+      JSONObject obj = (JSONObject) items.get(i);
+      parsedConf.set(obj.get("name").toString(),
+          obj.get("value").toString());
+    }
+    return parsedConf;
+  }
+
+  @Test
+  public void testGetSchedulerConf() throws Exception {
+    CapacitySchedulerConfiguration orgConf = getSchedulerConf();
+    assertNotNull(orgConf);
+    assertEquals(3, orgConf.getQueues("root").length);
+  }
+
   @Test
   public void testAddNestedQueue() throws Exception {
+    CapacitySchedulerConfiguration orgConf = getSchedulerConf();
+    assertNotNull(orgConf);
+    assertEquals(3, orgConf.getQueues("root").length);
+
     WebResource r = resource();
 
     ClientResponse response;
@@ -194,6 +230,10 @@ public class TestRMWebServicesConfigurationMutation extends JerseyTestBase {
         0.01f);
     assertEquals(75.0f, newCSConf.getNonLabeledQueueCapacity("root.d.d2"),
         0.01f);
+
+    CapacitySchedulerConfiguration newConf = getSchedulerConf();
+    assertNotNull(newConf);
+    assertEquals(4, newConf.getQueues("root").length);
   }
 
   @Test

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/markdown/ResourceManagerRest.md

@@ -4445,6 +4445,7 @@ Please note that this feature is currently in the alpha stage and is subject to
 
 ### HTTP Operations Supported
 
+      * GET
       * PUT
 
 ### Elements of the *sched-conf* object
@@ -4456,6 +4457,45 @@ Please note that this feature is currently in the alpha stage and is subject to
 | remove-queue | string | Full path name of a queue to remove |
 | global-updates | map | Map of key value pairs to update scheduler's global configuration |
 
+### GET Request Examples
+
+Get requests are used to retrieve the scheduler's configuration that is currently loaded into scheduler's context.
+
+**XML response**
+
+HTTP Request:
+
+      Accept: application/xml
+      Content-Type: application/xml
+      GET http://rm-http-address:port/ws/v1/cluster/scheduler-conf
+
+Response Header:
+
+      TTP/1.1 200 OK
+      Content-Type: application/xml; charset=utf-8
+      Transfer-Encoding: chunked
+
+Response Body:
+
+
+```xml
+      <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+      <configuration>
+        <property>
+          <name>yarn.scheduler.capacity.root.queues</name>
+          <value>default</value>
+        </property>
+        <property>
+          <name>yarn.scheduler.capacity.maximum-applications</name>
+          <value>10000</value>
+        </property>
+        <property>
+          <name>yarn.scheduler.capacity.root.default.capacity</name>
+          <value>100</value>
+        </property>
+      </configuration>
+```
+
 ### PUT Request Examples
 
 Put requests are used to modify the scheduler configuration. A successful mutation results in a 200 response. A malformed request or one which resulted in an invalid scheduler configuration results in a 400 response.