[autoscaler] Add an aggressive_autoscaling flag (#4285)

python/ray/autoscaler/autoscaler.py

@@ -51,6 +51,9 @@ CLUSTER_CONFIG_SCHEMA = {
     # The number of workers to launch initially, in addition to the head node.
     "initial_workers": (int, OPTIONAL),
 
+    # The mode of the autoscaler e.g. default, aggressive
+    "autoscaling_mode": (str, OPTIONAL),
+
     # The autoscaler will scale up the cluster to this target fraction of
     # resources usage. For example, if a cluster of 8 nodes is 100% busy
     # and target_utilization was 0.8, it would resize the cluster to 10.
@@ -519,9 +522,13 @@ class StandardAutoscaler(object):
         ideal_num_nodes = int(np.ceil(cur_used / float(target_frac)))
         ideal_num_workers = ideal_num_nodes - 1  # subtract 1 for head node
 
+        initial_workers = self.config["initial_workers"]
+        aggressive = self.config["autoscaling_mode"] == "aggressive"
         if self.bringup:
-            ideal_num_workers = max(ideal_num_workers,
-                                    self.config["initial_workers"])
+            ideal_num_workers = max(ideal_num_workers, initial_workers)
+        elif aggressive and cur_used > 0:
+            # If we want any workers, we want at least initial_workers
+            ideal_num_workers = max(ideal_num_workers, initial_workers)
 
         return min(self.config["max_workers"],
                    max(self.config["min_workers"], ideal_num_workers))