API improvements

changelog/6276.improvement.rst

@@ -0,0 +1 @@
+Allow Rasa to boot when model loading exception occurs. Forward HTTP Error responses to standard log output.

rasa/core/agent.py

@@ -85,9 +85,7 @@ def _load_interpreter(
         The NLU interpreter.
     """
     if nlu_path:
-        from rasa.core.interpreter import RasaNLUInterpreter
-
-        return RasaNLUInterpreter(model_directory=nlu_path)
+        return NaturalLanguageInterpreter.create(nlu_path)
 
     return agent.interpreter or RegexInterpreter()
 

rasa/core/run.py

@@ -246,16 +246,22 @@ async def load_agent_on_start(
 
     model_server = endpoints.model if endpoints and endpoints.model else None
 
-    app.agent = await agent.load_agent(
-        model_path,
-        model_server=model_server,
-        remote_storage=remote_storage,
-        interpreter=_interpreter,
-        generator=endpoints.nlg,
-        tracker_store=_tracker_store,
-        lock_store=_lock_store,
-        action_endpoint=endpoints.action,
-    )
+    try:
+        app.agent = await agent.load_agent(
+            model_path,
+            model_server=model_server,
+            remote_storage=remote_storage,
+            interpreter=_interpreter,
+            generator=endpoints.nlg,
+            tracker_store=_tracker_store,
+            lock_store=_lock_store,
+            action_endpoint=endpoints.action,
+        )
+    except Exception as e:
+        raise_warning(
+            f"The model at '{model_path}' could not be loaded. " f"Error: {e}"
+        )
+        app.agent = None
 
     if not app.agent:
         raise_warning(

rasa/server.py

@@ -85,6 +85,7 @@ def __init__(
             "code": status,
         }
         self.status = status
+        logger.error(message)
 
 
 def _docs(sub_url: Text) -> Text:

tests/core/test_run.py

@@ -1,4 +1,6 @@
-from rasa.core import run
+import pytest
+from rasa.core import run, interpreter, policies, domain
+from rasa.core.utils import AvailableEndpoints
 
 CREDENTIALS_FILE = "examples/moodbot/credentials.yml"
 
@@ -40,3 +42,38 @@ def test_create_single_input_channels_by_class_wo_credentials():
 
     assert len(channels) == 1
     assert channels[0].name() == "rest"
+
+
+async def test_load_agent_on_start_with_good_model_file(
+    trained_rasa_model, rasa_server, loop,
+):
+    agent = await run.load_agent_on_start(
+        trained_rasa_model, AvailableEndpoints(), None, rasa_server, loop,
+    )
+
+    assert isinstance(agent.interpreter, interpreter.RasaNLUInterpreter)
+    assert isinstance(agent.policy_ensemble, policies.PolicyEnsemble)
+    assert isinstance(agent.domain, domain.Domain)
+
+
+async def test_load_agent_on_start_with_bad_model_file(
+    tmpdir, rasa_server, loop,
+):
+    from pathlib import Path
+
+    fake_model = Path(tmpdir) / "fake_model.tar.gz"
+    fake_model.touch()
+    fake_model_path = str(fake_model)
+
+    with pytest.warns(UserWarning) as warnings:
+        agent = await run.load_agent_on_start(
+            fake_model_path, AvailableEndpoints(), None, rasa_server, loop,
+        )
+        assert any(
+            "fake_model.tar.gz' could not be loaded" in str(w.message) for w in warnings
+        )
+
+    # Fallback agent was loaded even if model was unusable
+    assert isinstance(agent.interpreter, interpreter.RegexInterpreter)
+    assert agent.policy_ensemble is None
+    assert isinstance(agent.domain, domain.Domain)