fix: host ip resolution uses ray vs socket

nemo_reinforcer/distributed/virtual_cluster.py

@@ -52,8 +52,7 @@ def _get_node_ip_and_free_port():
     import socket
 
     # Get the IP address of the current node
-    # Use socket.gethostbyname(socket.gethostname()) as a fallback
-    node_ip = socket.gethostbyname(socket.gethostname())
+    node_ip = ray._private.services.get_node_ip_address()
 
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
         s.bind(("", 0))  # Bind to port 0 to get a random free port

tests/unit/distributed/test_virtual_cluster.py

@@ -0,0 +1,32 @@
+# Copyright (c) 2025, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed 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.
+from nemo_reinforcer.distributed.virtual_cluster import (
+    _get_node_ip_and_free_port,
+    PY_EXECUTABLES,
+)
+import ray
+
+
+def test_get_node_ip_and_free_port_does_not_start_with_zero():
+    # This test covers a case where the hostname was an integer like "255"
+    # and socket returned an ip address equivalent to this hostname, i.e., "0.0.0.255".
+    # It's not possible to mock the way the hostname is actually set on other platforms,
+    # so we leave this test so we can ask users to run on their environment if needed.
+
+    node_ip, _ = ray.get(
+        _get_node_ip_and_free_port.options(
+            runtime_env={"py_executable": PY_EXECUTABLES.SYSTEM}
+        ).remote()
+    )
+    assert not node_ip.startswith("0."), "Node IP should not start with 0.*.*.*"