[dask] Add scheduler address to dask config.

doc/tutorials/dask.rst

@@ -475,6 +475,32 @@ interface, including callback functions, custom evaluation metric and objective:
     )
 
 
+.. _tracker-ip:
+
+***************
+Tracker Host IP
+***************
+
+.. versionadded:: 1.6.0
+
+In some environments XGBoost might fail to resolve the IP address of the scheduler, a
+symptom is user receiving ``OSError: [Errno 99] Cannot assign requested address`` error
+during training.  A quick workaround is to specify the address explicitly.  To do that
+dask config is used:
+
+.. code-block:: python
+
+    import dask
+    from distributed import Client
+    from xgboost import dask as dxgb
+    # let xgboost know the scheduler address
+    dask.config.set({"xgboost.scheduler_address": "192.0.0.100"})
+
+    with Client(scheduler_file="sched.json") as client:
+        reg = dxgb.DaskXGBRegressor()
+
+XGBoost will read configuration before training.
+
 *****************************************************************************
 Why is the initialization of ``DaskDMatrix``  so slow and throws weird errors
 *****************************************************************************

python-package/xgboost/dask.py

@@ -3,8 +3,12 @@
 # pylint: disable=too-many-lines, fixme
 # pylint: disable=too-few-public-methods
 # pylint: disable=import-error
-"""Dask extensions for distributed training. See :doc:`Distributed XGBoost with Dask
-</tutorials/dask>` for simple tutorial.  Also xgboost/demo/dask for some examples.
+"""
+Dask extensions for distributed training
+----------------------------------------
+
+See :doc:`Distributed XGBoost with Dask </tutorials/dask>` for simple tutorial.  Also
+:doc:`/python/dask-examples/index` for some examples.
 
 There are two sets of APIs in this module, one is the functional API including
 ``train`` and ``predict`` methods.  Another is stateful Scikit-Learner wrapper
@@ -13,10 +17,22 @@
 The implementation is heavily influenced by dask_xgboost:
 https://github.com/dask/dask-xgboost
 
+Optional dask configuration
+===========================
+
+- **xgboost.scheduler_address**: Specify the scheduler address, see :ref:`tracker-ip`.
+
+  .. versionadded:: 1.6.0
+
+  .. code-block:: python
+
+      dask.config.set({"xgboost.scheduler_address": "192.0.0.100"})
+
 """
 import platform
 import logging
 import collections
+import socket
 from contextlib import contextmanager
 from collections import defaultdict
 from threading import Thread
@@ -136,17 +152,37 @@ async def __aexit__(self, *args: Any, **kwargs: Any) -> None:
     return MultiLock
 
 
-def _start_tracker(n_workers: int) -> Dict[str, Any]:
-    """Start Rabit tracker """
-    env: Dict[str, Union[int, str]] = {'DMLC_NUM_WORKER': n_workers}
-    host = get_host_ip('auto')
-    rabit_context = RabitTracker(hostIP=host, n_workers=n_workers, use_logger=False)
-    env.update(rabit_context.worker_envs())
+def _try_start_tracker(
+    n_workers: int, addrs: List[Optional[str]]
+) -> Dict[str, Union[int, str]]:
+    env: Dict[str, Union[int, str]] = {"DMLC_NUM_WORKER": n_workers}
+    try:
+        rabit_context = RabitTracker(
+            hostIP=get_host_ip(addrs[0]), n_workers=n_workers, use_logger=False
+        )
+        env.update(rabit_context.worker_envs())
+        rabit_context.start(n_workers)
+        thread = Thread(target=rabit_context.join)
+        thread.daemon = True
+        thread.start()
+    except socket.error as e:
+        if len(addrs) < 2 or e.errno != 99:
+            raise
+        LOGGER.warning(
+            "Failed to bind address '%s', trying to use '%s' instead.",
+            str(addrs[0]),
+            str(addrs[1]),
+        )
+        env = _try_start_tracker(n_workers, addrs[1:])
 
-    rabit_context.start(n_workers)
-    thread = Thread(target=rabit_context.join)
-    thread.daemon = True
-    thread.start()
+    return env
+
+
+def _start_tracker(
+    n_workers: int, addr_from_dask: Optional[str], addr_from_user: Optional[str]
+) -> Dict[str, Any]:
+    """Start Rabit tracker, recurse to try different addresses."""
+    env = _try_start_tracker(n_workers, [get_host_ip(addr_from_user), addr_from_dask])
     return env
 
 
@@ -174,6 +210,7 @@ def __init__(self, args: List[bytes]) -> None:
 
     def __enter__(self) -> None:
         rabit.init(self.args)
+        assert rabit.is_distributed()
         LOGGER.debug('-------------- rabit say hello ------------------')
 
     def __exit__(self, *args: List) -> None:
@@ -805,12 +842,43 @@ def _dmatrix_from_list_of_parts(
     return _create_dmatrix(**kwargs)
 
 
-async def _get_rabit_args(n_workers: int, client: "distributed.Client") -> List[bytes]:
-    '''Get rabit context arguments from data distribution in DaskDMatrix.'''
-    env = await client.run_on_scheduler(_start_tracker, n_workers)
+async def _get_rabit_args(
+    n_workers: int, dconfig: Optional[Dict[str, Any]], client: "distributed.Client"
+) -> List[bytes]:
+    """Get rabit context arguments from data distribution in DaskDMatrix.
+
+    """
+    # There are 3 possible different addresses:
+    # 1. Provided by user via dask.config
+    # 2. Guessed by xgboost `get_host_ip` function
+    # 3. From dask scheduler
+    # We try 1 and 3 if 1 is available, otherwise 2 and 3.
+    valid_config = ["scheduler_address"]
+    # See if user config is available
+    if dconfig is not None:
+        for k in dconfig:
+            if k not in valid_config:
+                raise ValueError(f"Unknown configuration: {k}")
+        host_ip: Optional[str] = dconfig.get("scheduler_address", None)
+    else:
+        host_ip = None
+    # Try address from dask scheduler, this might not work, see
+    # https://github.com/dask/dask-xgboost/pull/40
+    try:
+        sched_addr = distributed.comm.get_address_host(client.scheduler.address)
+        sched_addr = sched_addr.strip("/:")
+    except Exception:  # pylint: disable=broad-except
+        sched_addr = None
+
+    env = await client.run_on_scheduler(_start_tracker, n_workers, sched_addr, host_ip)
+
     rabit_args = [f"{k}={v}".encode() for k, v in env.items()]
     return rabit_args
 
+
+def _get_dask_config() -> Optional[Dict[str, Any]]:
+    return dask.config.get("xgboost", default=None)
+
 # train and predict methods are supposed to be "functional", which meets the
 # dask paradigm.  But as a side effect, the `evals_result` in single-node API
 # is no longer supported since it mutates the input parameter, and it's not
@@ -837,6 +905,7 @@ def _get_workers_from_data(
 async def _train_async(
     client: "distributed.Client",
     global_config: Dict[str, Any],
+    dconfig: Optional[Dict[str, Any]],
     params: Dict[str, Any],
     dtrain: DaskDMatrix,
     num_boost_round: int,
@@ -850,7 +919,7 @@ async def _train_async(
     custom_metric: Optional[Metric],
 ) -> Optional[TrainReturnT]:
     workers = _get_workers_from_data(dtrain, evals)
-    _rabit_args = await _get_rabit_args(len(workers), client)
+    _rabit_args = await _get_rabit_args(len(workers), dconfig, client)
 
     if params.get("booster", None) == "gblinear":
         raise NotImplementedError(
@@ -948,7 +1017,7 @@ def dispatched_train(
 
 
 @_deprecate_positional_args
-def train(                      # pylint: disable=unused-argument
+def train(  # pylint: disable=unused-argument
     client: "distributed.Client",
     params: Dict[str, Any],
     dtrain: DaskDMatrix,
@@ -995,7 +1064,12 @@ def train(                      # pylint: disable=unused-argument
     _assert_dask_support()
     client = _xgb_get_client(client)
     args = locals()
-    return client.sync(_train_async, global_config=config.get_config(), **args)
+    return client.sync(
+        _train_async,
+        global_config=config.get_config(),
+        dconfig=_get_dask_config(),
+        **args,
+    )
 
 
 def _can_output_df(is_df: bool, output_shape: Tuple) -> bool:
@@ -1693,6 +1767,7 @@ async def _fit_async(
             asynchronous=True,
             client=self.client,
             global_config=config.get_config(),
+            dconfig=_get_dask_config(),
             params=params,
             dtrain=dtrain,
             num_boost_round=self.get_num_boosting_rounds(),
@@ -1796,6 +1871,7 @@ async def _fit_async(
             asynchronous=True,
             client=self.client,
             global_config=config.get_config(),
+            dconfig=_get_dask_config(),
             params=params,
             dtrain=dtrain,
             num_boost_round=self.get_num_boosting_rounds(),
@@ -1987,6 +2063,7 @@ async def _fit_async(
             asynchronous=True,
             client=self.client,
             global_config=config.get_config(),
+            dconfig=_get_dask_config(),
             params=params,
             dtrain=dtrain,
             num_boost_round=self.get_num_boosting_rounds(),

python-package/xgboost/tracker.py

@@ -192,7 +192,8 @@ def __init__(
         logging.info('start listen on %s:%d', hostIP, self.port)
 
     def __del__(self) -> None:
-        self.sock.close()
+        if hasattr(self, "sock"):
+            self.sock.close()
 
     @staticmethod
     def get_neighbor(rank: int, n_workers: int) -> List[int]:

tests/python-gpu/test_gpu_with_dask.py

@@ -371,7 +371,7 @@ def test_data_initialization(self, local_cuda_cluster: LocalCUDACluster) -> None
             m = dxgb.DaskDMatrix(client, X, y, feature_weights=fw)
 
             workers = _get_client_workers(client)
-            rabit_args = client.sync(dxgb._get_rabit_args, len(workers), client)
+            rabit_args = client.sync(dxgb._get_rabit_args, len(workers), None, client)
 
             def worker_fn(worker_addr: str, data_ref: Dict) -> None:
                 with dxgb.RabitContext(rabit_args):
@@ -473,7 +473,7 @@ def runit(
 
         with Client(local_cuda_cluster) as client:
             workers = _get_client_workers(client)
-            rabit_args = client.sync(dxgb._get_rabit_args, workers, client)
+            rabit_args = client.sync(dxgb._get_rabit_args, workers, None, client)
             futures = client.map(runit,
                                  workers,
                                  pure=False,

tests/python/test_tracker.py

@@ -28,7 +28,7 @@ def run_rabit_ops(client, n_workers):
     from xgboost import rabit
 
     workers = _get_client_workers(client)
-    rabit_args = client.sync(_get_rabit_args, len(workers), client)
+    rabit_args = client.sync(_get_rabit_args, len(workers), None, client)
     assert not rabit.is_distributed()
     n_workers_from_dask = len(workers)
     assert n_workers == n_workers_from_dask

tests/python/test_with_dask.py

@@ -30,6 +30,7 @@
     pytest.skip(msg=tm.no_dask()['reason'], allow_module_level=True)
 
 from distributed import LocalCluster, Client
+import dask
 import dask.dataframe as dd
 import dask.array as da
 from xgboost.dask import DaskDMatrix
@@ -1216,6 +1217,10 @@ def after_iteration(
         os.remove(before_fname)
         os.remove(after_fname)
 
+        with dask.config.set({'xgboost.foo': "bar"}):
+            with pytest.raises(ValueError):
+                xgb.dask.train(client, {}, dtrain, num_boost_round=4)
+
     def run_updater_test(
         self,
         client: "Client",
@@ -1315,7 +1320,8 @@ def runit(
             with Client(cluster) as client:
                 workers = _get_client_workers(client)
                 rabit_args = client.sync(
-                    xgb.dask._get_rabit_args, len(workers), client)
+                    xgb.dask._get_rabit_args, len(workers), None, client
+                )
                 futures = client.map(runit,
                                      workers,
                                      pure=False,
@@ -1443,7 +1449,9 @@ def test_no_duplicated_partition(self) -> None:
                 n_partitions = X.npartitions
                 m = xgb.dask.DaskDMatrix(client, X, y)
                 workers = _get_client_workers(client)
-                rabit_args = client.sync(xgb.dask._get_rabit_args, len(workers), client)
+                rabit_args = client.sync(
+                    xgb.dask._get_rabit_args, len(workers), None, client
+                )
                 n_workers = len(workers)
 
                 def worker_fn(worker_addr: str, data_ref: Dict) -> None: