[tests][dask] Use workers hostname in tests (fixes #4594) (#4595)

Co-authored-by: Nikita Titov <nekit94-12@hotmail.com>

tests/python_package_test/test_dask.py

@@ -9,6 +9,7 @@ from itertools import groupby
 from os import getenv
 from platform import machine
 from sys import platform
+from urllib.parse import urlparse
 
 import pytest
 
@@ -87,6 +88,11 @@ def listen_port():
 listen_port.port = 13000
 
 
+def _get_workers_hostname(cluster: LocalCluster) -> str:
+    one_worker_address = next(iter(cluster.scheduler_info['workers']))
+    return urlparse(one_worker_address).hostname
+
+
 def _create_ranking_data(n_samples=100, output='array', chunk_size=50, **kwargs):
     X, y, g = make_ranking(n_samples=n_samples, random_state=42, **kwargs)
     rnd = np.random.RandomState(42)
@@ -485,8 +491,9 @@ def test_training_does_not_fail_on_port_conflicts(cluster):
         _, _, _, _, dX, dy, dw, _ = _create_data('binary-classification', output='array')
 
         lightgbm_default_port = 12400
+        workers_hostname = _get_workers_hostname(cluster)
         with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-            s.bind(('127.0.0.1', lightgbm_default_port))
+            s.bind((workers_hostname, lightgbm_default_port))
             dask_classifier = lgb.DaskLGBMClassifier(
                 client=client,
                 time_out=5,
@@ -1395,13 +1402,14 @@ def test_network_params_not_required_but_respected_if_given(task, listen_port, c
         assert 'machines' not in params
 
         # model 2 - machines given
+        workers_hostname = _get_workers_hostname(cluster)
         n_workers = len(client.scheduler_info()['workers'])
         open_ports = lgb.dask._find_n_open_ports(n_workers)
         dask_model2 = dask_model_factory(
             n_estimators=5,
             num_leaves=5,
             machines=",".join([
-                f"127.0.0.1:{port}"
+                f"{workers_hostname}:{port}"
                 for port in open_ports
             ]),
         )
@@ -1442,12 +1450,13 @@ def test_machines_should_be_used_if_provided(task, cluster):
 
         n_workers = len(client.scheduler_info()['workers'])
         assert n_workers > 1
+        workers_hostname = _get_workers_hostname(cluster)
         open_ports = lgb.dask._find_n_open_ports(n_workers)
         dask_model = dask_model_factory(
             n_estimators=5,
             num_leaves=5,
             machines=",".join([
-                f"127.0.0.1:{port}"
+                f"{workers_hostname}:{port}"
                 for port in open_ports
             ]),
         )
@@ -1457,7 +1466,7 @@ def test_machines_should_be_used_if_provided(task, cluster):
         error_msg = f"Binding port {open_ports[0]} failed"
         with pytest.raises(lgb.basic.LightGBMError, match=error_msg):
             with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-                s.bind(('127.0.0.1', open_ports[0]))
+                s.bind((workers_hostname, open_ports[0]))
                 dask_model.fit(dX, dy, group=dg)
 
         # The above error leaves a worker waiting