[Serve] Good error message when Serve not installed and ensure Serve …

…installs ray[default] (ray-project#19570)

.buildkite/pipeline.yml

@@ -201,7 +201,8 @@
       python/ray/tests/test_basic_3
     - bazel test --test_output=streamed --config=ci --test_env=RAY_MINIMAL=1 $(./scripts/bazel_export_options)
       python/ray/tests/test_runtime_env_ray_minimal
-    # TODO(archit)
+    - bazel test --test_output=streamed --config=ci --test_env=RAY_MINIMAL=1 $(./scripts/bazel_export_options)
+      python/ray/tests/test_serve_ray_minimal
 - label: ":python: (Flaky tests)"
   conditions: ["RAY_CI_PYTHON_AFFECTED", "RAY_CI_SERVE_AFFECTED", "RAY_CI_RLLIB_AFFECTED", "RAY_CI_TUNE_AFFECTED"]
   commands:

python/ray/serve/__init__.py

@@ -1,7 +1,13 @@
-from ray.serve.api import (start, get_replica_context, shutdown, ingress,
-                           deployment, get_deployment, list_deployments)
-from ray.serve.batching import batch
-from ray.serve.config import HTTPOptions
+try:
+    from ray.serve.api import (start, get_replica_context, shutdown, ingress,
+                               deployment, get_deployment, list_deployments)
+    from ray.serve.batching import batch
+    from ray.serve.config import HTTPOptions
+except ModuleNotFoundError as e:
+    e.msg += (
+        ". You can run `pip install 'ray[serve]'` to install all Ray Serve"
+        " dependencies.")
+    raise e
 
 # Mute the warning because Serve sometimes intentionally calls
 # ray.get inside async actors.

python/ray/tests/BUILD

@@ -321,6 +321,14 @@ py_test(
     deps = ["//:ray_lib"],
 )
 
+py_test(
+    name = "test_serve_ray_minimal",
+    size = "small",
+    srcs = SRCS + ["test_serve_ray_minimal.py"],
+    tags = ["exclusive", "team:serve"],
+    deps = ["//:ray_lib"],
+)
+
 # TODO(ekl) we can't currently support tagging these as flaky since there's
 # no way to filter by both flaky and client mode tests in bazel.
 py_test_module_list(

python/ray/tests/test_serve_ray_minimal.py

@@ -0,0 +1,22 @@
+"""
+Test that Serve gives good error message when no deps are installed.
+This tests exist in the ray/tests/ directory instead of ray/serve/tests because
+it needs not to have dependencies on serve's conftest.py.
+"""
+
+import os
+
+import pytest
+
+
+@pytest.mark.skipif(
+    os.environ.get("RAY_MINIMAL") != "1",
+    reason="This test is only run in CI with a minimal Ray installation.")
+def test_error_msg():
+    with pytest.raises(ModuleNotFoundError, match="install 'ray\[serve\]'"):
+        from ray import serve
+        serve.start()
+
+
+if __name__ == "__main__":
+    pytest.main(["-v", "-s", __file__])

python/setup.py

@@ -211,6 +211,10 @@ def get_packages(self):
         ],
     }
 
+    # Ray Serve depends on the Ray dashboard components.
+    setup_spec.extras["serve"] = list(
+        set(setup_spec.extras["serve"] + setup_spec.extras["default"]))
+
     if RAY_EXTRA_CPP:
         setup_spec.extras["cpp"] = ["ray-cpp==" + setup_spec.version]