Autoscaling fixes.

- Initial targetWorkerCount must be subject to pool size limits
- Use consistent workerSetupData for the entire autoscaling run
- Don't call terminate() when we have nothing to terminate
- Terminate obsolete workers even faster

indexing-service/src/main/java/io/druid/indexing/overlord/scaling/SimpleResourceManagementStrategy.java

@@ -104,7 +104,7 @@ public class SimpleResourceManagementStrategy implements ResourceManagementStrat
       );
       currentlyProvisioning.removeAll(workerNodeIds);
 
-      updateTargetWorkerCount(pendingTasks, zkWorkers);
+      updateTargetWorkerCount(workerSetupData, pendingTasks, zkWorkers);
 
       int want = targetWorkerCount - (currValidWorkers + currentlyProvisioning.size());
       while (want > 0) {
@@ -180,16 +180,16 @@ public class SimpleResourceManagementStrategy implements ResourceManagementStrat
       currentlyTerminating.clear();
       currentlyTerminating.addAll(stillExisting);
 
-      updateTargetWorkerCount(pendingTasks, zkWorkers);
+      updateTargetWorkerCount(workerSetupData, pendingTasks, zkWorkers);
 
       final Predicate<ZkWorker> isLazyWorker = createLazyWorkerPredicate(config, workerSetupData);
       if (currentlyTerminating.isEmpty()) {
-        final int want = zkWorkers.size() - targetWorkerCount;
-        if (want > 0) {
+        final int excessWorkers = (zkWorkers.size() + currentlyProvisioning.size()) - targetWorkerCount;
+        if (excessWorkers > 0) {
           final List<String> laziestWorkerIps =
               FluentIterable.from(zkWorkers)
                             .filter(isLazyWorker)
-                            .limit(want)
+                            .limit(excessWorkers)
                             .transform(
                                 new Function<ZkWorker, String>()
                                 {
@@ -202,19 +202,23 @@ public class SimpleResourceManagementStrategy implements ResourceManagementStrat
                             )
                             .toList();
 
-          log.info(
-              "Terminating %,d workers (wanted %,d): %s",
-              laziestWorkerIps.size(),
-              want,
-              Joiner.on(", ").join(laziestWorkerIps)
-          );
+          if (laziestWorkerIps.isEmpty()) {
+            log.info("Wanted to terminate %,d workers, but couldn't find any lazy ones!");
+          } else {
+            log.info(
+                "Terminating %,d workers (wanted %,d): %s",
+                laziestWorkerIps.size(),
+                excessWorkers,
+                Joiner.on(", ").join(laziestWorkerIps)
+            );
 
-          final AutoScalingData terminated = autoScalingStrategy.terminate(laziestWorkerIps);
-          if (terminated != null) {
-            currentlyTerminating.addAll(terminated.getNodeIds());
-            lastTerminateTime = new DateTime();
-            scalingStats.addTerminateEvent(terminated);
-            didTerminate = true;
+            final AutoScalingData terminated = autoScalingStrategy.terminate(laziestWorkerIps);
+            if (terminated != null) {
+              currentlyTerminating.addAll(terminated.getNodeIds());
+              lastTerminateTime = new DateTime();
+              scalingStats.addTerminateEvent(terminated);
+              didTerminate = true;
+            }
           }
         }
       } else {
@@ -283,12 +287,12 @@ public class SimpleResourceManagementStrategy implements ResourceManagementStrat
   }
 
   private void updateTargetWorkerCount(
+      final WorkerSetupData workerSetupData,
       final Collection<RemoteTaskRunnerWorkItem> pendingTasks,
       final Collection<ZkWorker> zkWorkers
   )
   {
     synchronized (lock) {
-      final WorkerSetupData workerSetupData = workerSetupDataRef.get();
       final Collection<ZkWorker> validWorkers = Collections2.filter(
           zkWorkers,
           createValidWorkerPredicate(config, workerSetupData)
@@ -296,8 +300,14 @@ public class SimpleResourceManagementStrategy implements ResourceManagementStrat
       final Predicate<ZkWorker> isLazyWorker = createLazyWorkerPredicate(config, workerSetupData);
 
       if (targetWorkerCount < 0) {
-        // Initialize to size of current worker pool
-        targetWorkerCount = zkWorkers.size();
+        // Initialize to size of current worker pool, subject to pool size limits
+        targetWorkerCount = Math.max(
+            Math.min(
+                zkWorkers.size(),
+                workerSetupData.getMaxNumWorkers()
+            ),
+            workerSetupData.getMinNumWorkers()
+        );
         log.info(
             "Starting with a target of %,d workers (current = %,d, min = %,d, max = %,d).",
             targetWorkerCount,