refactor: install external providers from module (#2637)

# What does this PR do?

Today, external providers are installed via the `external_providers_dir`
in the config. This necessitates users to understand the `ProviderSpec`
and set up their directories accordingly. This process splits up the
config for the stack across multiple files, directories, and formats.

Most (if not all) external providers today have a
[get_provider_spec](559cb18fbb/src/ramalama_stack/provider.py (L9))
method that sits unused. Utilizing this method rather than the
providers.d route allows for a much easier installation process for
external providers and limits the amount of extra configuration a
regular user has to do to get their stack off the ground.

To accomplish this and wire it throughout the build process, Introduce
the concept of a `module` for users to specify for an external provider
upon build time. In order to facilitate this, align the build and run
spec to use `Provider` class rather than the stringified provider_type
that build currently uses.

For example, say this is in your build config:

```
- provider_id: ramalama
  provider_type: remote::ramalama
  module: ramalama_stack
```

during build (in the various `build_...` scripts), additionally to
installing any pip dependencies we will also install this module and use
the `get_provider_spec` method to retrieve the ProviderSpec that is
currently specified using `providers.d`.

In production so far, providing instructions for installing external
providers for users has been difficult: they need to install the module
as a pre-req, create the providers.d directory, copy in the provider
spec, and also copy in the necessary build/run yaml files. Accessing an
external provider should be as easy as possible, and pointing to its
installable module aligns more with the rest of our build and dependency
management process.

For now, `external_providers_dir` still exists as an alternate more
declarative method of using external providers.

## Test Plan

added an integration test installing an external provider from module
and more unit test coverage for `get_provider_registry`


( the warning in yellow is expected, the module is installed inside of
the build env, not where we are running the command)
<img width="1119" height="400" alt="Screenshot 2025-07-24 at 11 30
48 AM"
src="https://github.com/user-attachments/assets/1efbaf45-b9e8-451a-bd63-264ed664706d"
/>

<img width="1154" height="618" alt="Screenshot 2025-07-24 at 11 31
14 AM"
src="https://github.com/user-attachments/assets/feb2b3ea-c5dd-418e-9662-9a3bd5dd6bdc"
/>

---------

Signed-off-by: Charlie Doern <cdoern@redhat.com>

tests/external/build.yaml

@@ -3,7 +3,8 @@ distribution_spec:
   description: Custom distro for CI tests
   providers:
     weather:
-    - remote::kaze
+    - provider_id: kaze
+      provider_type: remote::kaze
 image_type: venv
 image_name: ci-test
 external_providers_dir: ~/.llama/providers.d

tests/external/ramalama-stack/build.yaml

@@ -0,0 +1,14 @@
+version: 2
+distribution_spec:
+  description: Use (an external) Ramalama server for running LLM inference
+  container_image: null
+  providers:
+    inference:
+    - provider_id: ramalama
+      provider_type: remote::ramalama
+      module: ramalama_stack==0.3.0a0
+image_type: venv
+image_name: ramalama-stack-test
+additional_pip_packages:
+- aiosqlite
+- sqlalchemy[asyncio]

tests/external/ramalama-stack/run.yaml

@@ -0,0 +1,12 @@
+version: 2
+image_name: ramalama
+apis:
+- inference
+providers:
+  inference:
+  - provider_id: ramalama
+    provider_type: remote::ramalama
+    module: ramalama_stack==0.3.0a0
+    config: {}
+server:
+  port: 8321

tests/unit/distribution/test_distribution.py

@@ -106,6 +106,40 @@ def api_directories(tmp_path):
     return remote_inference_dir, inline_inference_dir
 
 
+def make_import_module_side_effect(
+    builtin_provider_spec=None,
+    external_module=None,
+    raise_for_external=False,
+    missing_get_provider_spec=False,
+):
+    from types import SimpleNamespace
+
+    def import_module_side_effect(name):
+        if name == "llama_stack.providers.registry.inference":
+            mock_builtin = SimpleNamespace(
+                available_providers=lambda: [
+                    builtin_provider_spec
+                    or ProviderSpec(
+                        api=Api.inference,
+                        provider_type="test_provider",
+                        config_class="test_provider.config.TestProviderConfig",
+                        module="test_provider",
+                    )
+                ]
+            )
+            return mock_builtin
+        elif name == "external_test.provider":
+            if raise_for_external:
+                raise ModuleNotFoundError(name)
+            if missing_get_provider_spec:
+                return SimpleNamespace()
+            return external_module
+        else:
+            raise ModuleNotFoundError(name)
+
+    return import_module_side_effect
+
+
 class TestProviderRegistry:
     """Test suite for provider registry functionality."""
 
@@ -221,3 +255,124 @@ pip_packages:
         with pytest.raises(KeyError) as exc_info:
             get_provider_registry(base_config)
         assert "config_class" in str(exc_info.value)
+
+    def test_external_provider_from_module_success(self, mock_providers):
+        """Test loading an external provider from a module (success path)."""
+        from types import SimpleNamespace
+
+        from llama_stack.distribution.datatypes import Provider, StackRunConfig
+        from llama_stack.providers.datatypes import Api, ProviderSpec
+
+        # Simulate a provider module with get_provider_spec
+        fake_spec = ProviderSpec(
+            api=Api.inference,
+            provider_type="external_test",
+            config_class="external_test.config.ExternalTestConfig",
+            module="external_test",
+        )
+        fake_module = SimpleNamespace(get_provider_spec=lambda: fake_spec)
+
+        import_module_side_effect = make_import_module_side_effect(external_module=fake_module)
+
+        with patch("importlib.import_module", side_effect=import_module_side_effect) as mock_import:
+            config = StackRunConfig(
+                image_name="test_image",
+                providers={
+                    "inference": [
+                        Provider(
+                            provider_id="external_test",
+                            provider_type="external_test",
+                            config={},
+                            module="external_test",
+                        )
+                    ]
+                },
+            )
+            registry = get_provider_registry(config)
+            assert Api.inference in registry
+            assert "external_test" in registry[Api.inference]
+            provider = registry[Api.inference]["external_test"]
+            assert provider.module == "external_test"
+            assert provider.config_class == "external_test.config.ExternalTestConfig"
+            mock_import.assert_any_call("llama_stack.providers.registry.inference")
+            mock_import.assert_any_call("external_test.provider")
+
+    def test_external_provider_from_module_not_found(self, mock_providers):
+        """Test handling ModuleNotFoundError for missing provider module."""
+        from llama_stack.distribution.datatypes import Provider, StackRunConfig
+
+        import_module_side_effect = make_import_module_side_effect(raise_for_external=True)
+
+        with patch("importlib.import_module", side_effect=import_module_side_effect):
+            config = StackRunConfig(
+                image_name="test_image",
+                providers={
+                    "inference": [
+                        Provider(
+                            provider_id="external_test",
+                            provider_type="external_test",
+                            config={},
+                            module="external_test",
+                        )
+                    ]
+                },
+            )
+            with pytest.raises(ValueError) as exc_info:
+                get_provider_registry(config)
+            assert "get_provider_spec not found" in str(exc_info.value)
+
+    def test_external_provider_from_module_missing_get_provider_spec(self, mock_providers):
+        """Test handling missing get_provider_spec in provider module (should raise ValueError)."""
+        from llama_stack.distribution.datatypes import Provider, StackRunConfig
+
+        import_module_side_effect = make_import_module_side_effect(missing_get_provider_spec=True)
+
+        with patch("importlib.import_module", side_effect=import_module_side_effect):
+            config = StackRunConfig(
+                image_name="test_image",
+                providers={
+                    "inference": [
+                        Provider(
+                            provider_id="external_test",
+                            provider_type="external_test",
+                            config={},
+                            module="external_test",
+                        )
+                    ]
+                },
+            )
+            with pytest.raises(AttributeError):
+                get_provider_registry(config)
+
+    def test_external_provider_from_module_building(self, mock_providers):
+        """Test loading an external provider from a module during build (building=True, partial spec)."""
+        from llama_stack.distribution.datatypes import BuildConfig, DistributionSpec, Provider
+        from llama_stack.providers.datatypes import Api
+
+        # No importlib patch needed, should not import module when type of `config` is BuildConfig or DistributionSpec
+        build_config = BuildConfig(
+            version=2,
+            image_type="container",
+            image_name="test_image",
+            distribution_spec=DistributionSpec(
+                description="test",
+                providers={
+                    "inference": [
+                        Provider(
+                            provider_id="external_test",
+                            provider_type="external_test",
+                            config={},
+                            module="external_test",
+                        )
+                    ]
+                },
+            ),
+        )
+        registry = get_provider_registry(build_config)
+        assert Api.inference in registry
+        assert "external_test" in registry[Api.inference]
+        provider = registry[Api.inference]["external_test"]
+        assert provider.module == "external_test"
+        assert provider.is_external is True
+        # config_class is empty string in partial spec
+        assert provider.config_class == ""