[Serve] Add dependency management support for driver not running in a conda env (#13269)

python/ray/serve/examples/doc/imported_backend.py

@@ -5,6 +5,7 @@ from ray.serve.backends import ImportedBackend
 
 client = serve.start()
 
+# Include your class as input to the ImportedBackend constructor.
 backend_class = ImportedBackend("ray.serve.utils.MockImportedBackend")
 client.create_backend("imported", backend_class, "input_arg")
 client.create_endpoint("imported", backend="imported", route="/imported")

python/ray/serve/utils.py

@@ -11,6 +11,7 @@ from typing import Iterable, List, Dict, Tuple
 import os
 from ray.serve.exceptions import RayServeException
 from collections import UserDict
+from pathlib import Path
 
 import starlette.requests
 import requests
@@ -180,13 +181,21 @@ def format_actor_name(actor_name, controller_name=None, *modifiers):
 
 def get_conda_env_dir(env_name):
     """Given a environment name like `tf1`, find and validate the
-    corresponding conda directory.
+    corresponding conda directory. Untested on Windows.
     """
     conda_prefix = os.environ.get("CONDA_PREFIX")
     if conda_prefix is None:
-        raise ValueError(
-            "Serve cannot find environment variables installed by conda. " +
-            "Are you sure you are in a conda env?")
+        # The caller is neither in a conda env or in (base).  This is rare
+        # because by default, new terminals start in (base), but we can still
+        # support this case.
+        conda_exe = os.environ.get("CONDA_EXE")
+        if conda_exe is None:
+            raise RayServeException(
+                "Ray Serve cannot find environment variables set by conda. "
+                "Please verify conda is installed.")
+        # Example: CONDA_EXE=$HOME/anaconda3/bin/python
+        # Strip out the /bin/python by going up two parent directories.
+        conda_prefix = str(Path(conda_exe).parent.parent)
 
     # There are two cases:
     # 1. We are in conda base env: CONDA_DEFAULT_ENV=base and