YARN-10397. SchedulerRequest should be forwarded to scheduler if custom scheduler supports placement constraints. Contributed by Bilwa S T.

(cherry picked from commit 43572fc7f8)

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

@@ -884,6 +884,15 @@ public Set<String> getPlanQueues() throws YarnException {
         + " does not support reservations");
   }
 
+  /**
+   * By default placement constraint is disabled. Schedulers which support
+   * placement constraint can override this value.
+   * @return enabled or not
+   */
+  public boolean placementConstraintEnabled() {
+    return false;
+  }
+
   protected void refreshMaximumAllocation(Resource newMaxAlloc) {
     nodeTracker.setConfiguredMaxAllocation(newMaxAlloc);
   }

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

@@ -3285,4 +3285,12 @@ public int getNumAsyncSchedulerThreads() {
   public void setMaxRunningAppsEnforcer(CSMaxRunningAppsEnforcer enforcer) {
     this.maxRunningEnforcer = enforcer;
   }
+
+  /**
+   * Returning true as capacity scheduler supports placement constraints.
+   */
+  @Override
+  public boolean placementConstraintEnabled() {
+    return true;
+  }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/constraint/processor/SchedulerPlacementProcessor.java

@@ -22,7 +22,6 @@
 import org.apache.hadoop.yarn.api.protocolrecords.AllocateResponse;
 import org.apache.hadoop.yarn.api.records.ApplicationAttemptId;
 import org.apache.hadoop.yarn.exceptions.YarnException;
-import org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -39,7 +38,7 @@ public void allocate(ApplicationAttemptId appAttemptId,
       AllocateRequest request, AllocateResponse response) throws YarnException {
     if (request.getSchedulingRequests() != null
         && !request.getSchedulingRequests().isEmpty()) {
-      if (!(scheduler instanceof CapacityScheduler)) {
+      if (!scheduler.placementConstraintEnabled()) {
         String message = "Found non empty SchedulingRequest of "
             + "AllocateRequest for application=" + appAttemptId.toString()
             + ", however the configured scheduler="