[core][autoscaler] Autoscaler v2 does not honor minReplicas/replicas count of the worker nodes and constantly terminates after idletimeout

python/ray/autoscaler/v2/scheduler.py

@@ -1568,6 +1568,10 @@ def _enforce_idle_termination(
         Args:
             ctx: The schedule context.
         """
+        count_by_node_type = ctx.get_cluster_shape()
+        node_type_configs = ctx.get_node_type_configs()
+        terminate_nodes_by_type: Dict[NodeType, int] = defaultdict(int)
+
         nodes = ctx.get_nodes()
         s_to_ms = 1000
         for node in nodes:
@@ -1600,6 +1604,19 @@ def _enforce_idle_termination(
                     )
                 continue
 
+            # Honor the min_worker_nodes setting for the node type.
+            min_count = 0
+            node_type = node.node_type
+            if node_type in node_type_configs:
+                min_count = node_type_configs[node_type].min_worker_nodes
+            if (
+                count_by_node_type.get(node_type, 0)
+                - terminate_nodes_by_type[node_type]
+                <= min_count
+            ):
+                continue
+
+            terminate_nodes_by_type[node.node_type] += 1
             # The node is idle for too long, terminate it.
             node.status = SchedulingNodeStatus.TO_TERMINATE
             node.termination_request = TerminationRequest(

python/ray/autoscaler/v2/tests/test_scheduler.py

@@ -1349,6 +1349,91 @@ def test_idle_termination(idle_timeout_s, has_resource_constraints):
         assert len(to_terminate) == 0
 
 
+@pytest.mark.parametrize("min_workers", [0, 1])
+def test_idle_termination_with_min_worker(min_workers):
+    """
+    Test that idle nodes are terminated.
+    """
+    idle_timeout_s = 1
+
+    scheduler = ResourceDemandScheduler(event_logger)
+
+    node_type_configs = {
+        "type_cpu": NodeTypeConfig(
+            name="type_cpu",
+            resources={"CPU": 1},
+            min_worker_nodes=min_workers,
+            max_worker_nodes=5,
+            launch_config_hash="hash1",
+        ),
+        "head_node": NodeTypeConfig(
+            name="head_node",
+            resources={"CPU": 0},
+            launch_config_hash="hash2",
+            min_worker_nodes=0,
+            max_worker_nodes=1,
+        ),
+    }
+
+    idle_time_s = 5
+    constraints = []
+
+    request = sched_request(
+        node_type_configs=node_type_configs,
+        instances=[
+            make_autoscaler_instance(
+                im_instance=Instance(
+                    instance_id="i-1",
+                    instance_type="type_cpu",
+                    status=Instance.RAY_RUNNING,
+                    launch_config_hash="hash1",
+                    node_id="r-1",
+                ),
+                ray_node=NodeState(
+                    ray_node_type_name="type_cpu",
+                    node_id=b"r-1",
+                    available_resources={"CPU": 1},
+                    total_resources={"CPU": 1},
+                    idle_duration_ms=idle_time_s * 1000,
+                    status=NodeStatus.IDLE,
+                ),
+                cloud_instance_id="c-1",
+            ),
+            make_autoscaler_instance(
+                im_instance=Instance(
+                    instance_id="i-2",
+                    instance_type="head_node",
+                    status=Instance.RAY_RUNNING,
+                    launch_config_hash="hash2",
+                    node_kind=NodeKind.HEAD,
+                    node_id="r-2",
+                ),
+                ray_node=NodeState(
+                    ray_node_type_name="head_node",
+                    node_id=b"r-2",
+                    available_resources={"CPU": 0},
+                    total_resources={"CPU": 0},
+                    idle_duration_ms=999 * 1000,  # idle
+                    status=NodeStatus.IDLE,
+                ),
+                cloud_instance_id="c-2",
+            ),
+        ],
+        idle_timeout_s=idle_timeout_s,
+        cluster_resource_constraints=constraints,
+    )
+
+    reply = scheduler.schedule(request)
+    _, to_terminate = _launch_and_terminate(reply)
+    assert idle_timeout_s <= idle_time_s
+    if min_workers == 0:
+        assert len(to_terminate) == 1
+        assert to_terminate == [("i-1", "r-1", TerminationRequest.Cause.IDLE)]
+    else:
+        assert min_workers > 0
+        assert len(to_terminate) == 0
+
+
 def test_gang_scheduling():
     """
     Test that gang scheduling works.