Use RAY_ADDRESS to connect to an existing Ray cluster if present

python/ray/tests/test_advanced_3.py

@@ -689,6 +689,32 @@ def f(x):
     assert len(ray.objects()) == 0, ray.objects()
 
 
+@pytest.mark.parametrize(
+    "ray_start_cluster", [{
+        "num_cpus": 0,
+        "num_nodes": 1,
+        "do_init": False,
+    }],
+    indirect=True)
+def test_ray_address_environment_variable(ray_start_cluster):
+    address = ray_start_cluster.address
+    # In this test we use zero CPUs to distinguish between starting a local
+    # ray cluster and connecting to an existing one.
+
+    # Make sure we connect to an existing cluster if
+    # RAY_ADDRESS is set.
+    os.environ["RAY_ADDRESS"] = address
+    ray.init()
+    assert "CPU" not in ray.state.cluster_resources()
+    del os.environ["RAY_ADDRESS"]
+    ray.shutdown()
+
+    # Make sure we start a new cluster if RAY_ADDRESS is not set.
+    ray.init()
+    assert "CPU" in ray.state.cluster_resources()
+    ray.shutdown()
+
+
 if __name__ == "__main__":
     import pytest
     sys.exit(pytest.main(["-v", __file__]))

python/ray/util/joblib/ray_backend.py

@@ -5,8 +5,6 @@
 from ray.util.multiprocessing.pool import Pool
 import ray
 
-RAY_ADDRESS_ENV = "RAY_ADDRESS"
-
 logger = logging.getLogger(__name__)
 
 
@@ -34,15 +32,13 @@ def configure(self,
         if n_jobs == -1:
             if not ray.is_initialized():
                 import os
-                if RAY_ADDRESS_ENV in os.environ:
-                    ray_address = os.environ[RAY_ADDRESS_ENV]
+                if "RAY_ADDRESS" in os.environ:
                     logger.info(
                         "Connecting to ray cluster at address='{}'".format(
-                            ray_address))
-                    ray.init(address=ray_address)
+                            os.environ["RAY_ADDRESS"]))
                 else:
                     logger.info("Starting local ray cluster")
-                    ray.init()
+                ray.init()
             ray_cpus = int(ray.state.cluster_resources()["CPU"])
             n_jobs = ray_cpus
 

python/ray/util/multiprocessing/pool.py

@@ -349,11 +349,12 @@ def _init_ray(self, processes=None, ray_address=None):
         # Else, the priority is:
         # ray_address argument > RAY_ADDRESS > start new local cluster.
         if not ray.is_initialized():
-            if ray_address is None and RAY_ADDRESS_ENV in os.environ:
-                ray_address = os.environ[RAY_ADDRESS_ENV]
-
             # Cluster mode.
-            if ray_address is not None:
+            if ray_address is None and RAY_ADDRESS_ENV in os.environ:
+                logger.info("Connecting to ray cluster at address='{}'".format(
+                    os.environ[RAY_ADDRESS_ENV]))
+                ray.init()
+            elif ray_address is not None:
                 logger.info("Connecting to ray cluster at address='{}'".format(
                     ray_address))
                 ray.init(address=ray_address)

python/ray/worker.py

@@ -565,6 +565,10 @@ def init(address=None,
 
         ray.init(address="123.45.67.89:6379")
 
+    You can also define an environment variable called `RAY_ADDRESS` in
+    the same format as the `address` parameter to connect to an existing
+    cluster with ray.init().
+
     Args:
         address (str): The address of the Ray cluster to connect to. If
             this address is not provided, then this command will start Redis,
@@ -672,6 +676,17 @@ def init(address=None,
         raise DeprecationWarning("The redis_address argument is deprecated. "
                                  "Please use address instead.")
 
+    if "RAY_ADDRESS" in os.environ:
+        if redis_address is None and (address is None or address == "auto"):
+            address = os.environ["RAY_ADDRESS"]
+        else:
+            raise RuntimeError(
+                "Cannot use both the RAY_ADDRESS environment variable and "
+                "the address argument of ray.init simultaneously. If you "
+                "use RAY_ADDRESS to connect to a specific Ray cluster, "
+                "please call ray.init() or ray.init(address=\"auto\") on the "
+                "driver.")
+
     if redis_address is not None or address is not None:
         redis_address, _, _ = services.validate_redis_address(
             address, redis_address)