[App] Add status endpoint, enable ready

examples/app_boring/app.py

@@ -43,6 +43,10 @@ def __init__(self):
             raise_exception=True,
         )
 
+    @property
+    def ready(self) -> bool:
+        return self.dest_work.is_running
+
     def run(self):
         self.source_work.run()
         if self.source_work.has_succeeded:

src/lightning_app/components/serve/streamlit.py

@@ -20,6 +20,8 @@ class ServeStreamlit(LightningWork, abc.ABC):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
+        self.ready = False
+
         self._process = None
 
     @property
@@ -58,6 +60,7 @@ def run(self) -> None:
             ],
             env=env,
         )
+        self.ready = True
         self._process.wait()
 
     def on_exit(self) -> None:

src/lightning_app/core/api.py

@@ -34,6 +34,7 @@
 from lightning_app.core.queues import QueuingSystem
 from lightning_app.storage import Drive
 from lightning_app.utilities.app_helpers import InMemoryStateStore, Logger, StateStore
+from lightning_app.utilities.app_status import AppStatus
 from lightning_app.utilities.cloud import is_running_in_cloud
 from lightning_app.utilities.component import _context
 from lightning_app.utilities.enum import ComponentContext, OpenAPITags
@@ -66,18 +67,24 @@ class SessionMiddleware:
 lock = Lock()
 
 app_spec: Optional[List] = None
+app_status: Optional[AppStatus] = None
+
 # In the future, this would be abstracted to support horizontal scaling.
 responses_store = {}
 
 logger = Logger(__name__)
 
-
 # This can be replaced with a consumer that publishes states in a kv-store
 # in a serverless architecture
 
 
 class UIRefresher(Thread):
-    def __init__(self, api_publish_state_queue, api_response_queue, refresh_interval: float = 0.1) -> None:
+    def __init__(
+        self,
+        api_publish_state_queue,
+        api_response_queue,
+        refresh_interval: float = 0.1,
+    ) -> None:
         super().__init__(daemon=True)
         self.api_publish_state_queue = api_publish_state_queue
         self.api_response_queue = api_response_queue
@@ -98,7 +105,8 @@ def run(self):
 
     def run_once(self):
         try:
-            state = self.api_publish_state_queue.get(timeout=0)
+            global app_status
+            state, app_status = self.api_publish_state_queue.get(timeout=0)
             with lock:
                 global_app_state_store.set_app_state(TEST_SESSION_UUID, state)
         except queue.Empty:
@@ -326,6 +334,17 @@ async def upload_file(response: Response, filename: str, uploaded_file: UploadFi
     return f"Successfully uploaded '{filename}' to the Drive"
 
 
+@fastapi_service.get("/api/v1/status", response_model=AppStatus)
+async def get_status() -> AppStatus:
+    """Get the current status of the app and works."""
+    global app_status
+    if app_status is None:
+        raise HTTPException(
+            status_code=status.HTTP_503_SERVICE_UNAVAILABLE, detail="App status hasn't been reported yet."
+        )
+    return app_status
+
+
 @fastapi_service.get("/healthz", status_code=200)
 async def healthz(response: Response):
     """Health check endpoint used in the cloud FastAPI servers to check the status periodically."""

src/lightning_app/core/app.py

@@ -35,6 +35,7 @@
     _should_dispatch_app,
     Logger,
 )
+from lightning_app.utilities.app_status import AppStatus
 from lightning_app.utilities.commands.base import _process_requests
 from lightning_app.utilities.component import _convert_paths_after_init, _validate_root_flow
 from lightning_app.utilities.enum import AppStage, CacheCallsKeys
@@ -140,6 +141,7 @@ def __init__(
         self.exception = None
         self.collect_changes: bool = True
 
+        self.status: Optional[AppStatus] = None
         # TODO: Enable ready locally for opening the UI.
         self.ready = False
 
@@ -150,6 +152,7 @@ def __init__(
         self.checkpointing: bool = False
 
         self._update_layout()
+        self._update_status()
 
         self.is_headless: Optional[bool] = None
 
@@ -418,6 +421,7 @@ def run_once(self):
 
         self._update_layout()
         self._update_is_headless()
+        self._update_status()
         self.maybe_apply_changes()
 
         if self.checkpointing and self._should_snapshot():
@@ -485,19 +489,12 @@ def _run(self) -> bool:
         self._original_state = deepcopy(self.state)
         done = False
 
-        # TODO: Re-enable the `ready` property once issues are resolved
-        if not self.root.ready:
-            warnings.warn(
-                "One of your Flows returned `.ready` as `False`. "
-                "This feature is not yet enabled so this will be ignored.",
-                UserWarning,
-            )
-        self.ready = True
+        self.ready = self.root.ready
 
         self._start_with_flow_works()
 
-        if self.ready and self.should_publish_changes_to_api and self.api_publish_state_queue:
-            self.api_publish_state_queue.put(self.state_vars)
+        if self.should_publish_changes_to_api and self.api_publish_state_queue is not None:
+            self.api_publish_state_queue.put((self.state_vars, self.status))
 
         self._reset_run_time_monitor()
 
@@ -506,8 +503,8 @@ def _run(self) -> bool:
 
             self._update_run_time_monitor()
 
-            if self.ready and self._has_updated and self.should_publish_changes_to_api and self.api_publish_state_queue:
-                self.api_publish_state_queue.put(self.state_vars)
+            if self._has_updated and self.should_publish_changes_to_api and self.api_publish_state_queue is not None:
+                self.api_publish_state_queue.put((self.state_vars, self.status))
 
             self._has_updated = False
 
@@ -532,6 +529,23 @@ def _update_is_headless(self) -> None:
         # This ensures support for apps which dynamically add a UI at runtime.
         _handle_is_headless(self)
 
+    def _update_status(self) -> None:
+        old_status = self.status
+
+        work_statuses = {}
+        for work in breadth_first(self.root, types=(lightning_app.LightningWork,)):
+            work_statuses[work.name] = work.status
+
+        self.status = AppStatus(
+            is_ui_ready=self.ready,
+            work_statuses=work_statuses,
+        )
+
+        # If the work statuses changed, the state delta will trigger an update.
+        # If ready has changed, we trigger an update manually.
+        if self.status != old_status:
+            self._has_updated = True
+
     def _apply_restarting(self) -> bool:
         self._reset_original_state()
         # apply stage after restoring the original state.

src/lightning_app/core/flow.py

@@ -249,10 +249,7 @@ def __getattr__(self, item):
 
     @property
     def ready(self) -> bool:
-        """Not currently enabled.
-
-        Override to customize when your App should be ready.
-        """
+        """Override to customize when your App should be ready."""
         flows = self.flows
         return all(flow.ready for flow in flows.values()) if flows else True
 

src/lightning_app/core/work.py

@@ -12,13 +12,13 @@
 from lightning_app.storage.drive import _maybe_create_drive, Drive
 from lightning_app.storage.payload import Payload
 from lightning_app.utilities.app_helpers import _is_json_serializable, _LightningAppRef, is_overridden
+from lightning_app.utilities.app_status import WorkStatus
 from lightning_app.utilities.component import _is_flow_context, _sanitize_state
 from lightning_app.utilities.enum import (
     CacheCallsKeys,
     make_status,
     WorkFailureReasons,
     WorkStageStatus,
-    WorkStatus,
     WorkStopReasons,
 )
 from lightning_app.utilities.exceptions import LightningWorkException

src/lightning_app/runners/runtime.py

@@ -121,7 +121,7 @@ def terminate(self) -> None:
                         self._add_stopped_status_to_work(work)
 
                     # Publish the updated state and wait for the frontend to update.
-                    self.app.api_publish_state_queue.put(self.app.state)
+                    self.app.api_publish_state_queue.put((self.app.state, self.app.status))
 
                 for thread in self.threads + self.app.threads:
                     thread.join(timeout=0)

src/lightning_app/utilities/app_status.py

@@ -0,0 +1,29 @@
+from datetime import datetime
+from typing import Any, Dict, Optional
+
+from pydantic import BaseModel
+
+
+class WorkStatus(BaseModel):
+    """The ``WorkStatus`` captures the status of a work according to the app."""
+
+    stage: str
+    timestamp: float
+    reason: Optional[str] = None
+    message: Optional[str] = None
+    count: int = 1
+
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        super().__init__(*args, **kwargs)
+
+        assert self.timestamp > 0 and self.timestamp < (int(datetime.now().timestamp()) + 10)
+
+
+class AppStatus(BaseModel):
+    """The ``AppStatus`` captures the current status of the app and its components."""
+
+    # ``True`` when the app UI is ready to be viewed
+    is_ui_ready: bool
+
+    # The statuses of ``LightningWork`` objects currently associated with this app
+    work_statuses: Dict[str, WorkStatus]

src/lightning_app/utilities/enum.py

@@ -1,5 +1,4 @@
 import enum
-from dataclasses import dataclass
 from datetime import datetime, timezone
 from typing import Optional
 
@@ -47,18 +46,6 @@ class WorkStageStatus:
     FAILED = "failed"
 
 
-@dataclass
-class WorkStatus:
-    stage: WorkStageStatus
-    timestamp: float
-    reason: Optional[str] = None
-    message: Optional[str] = None
-    count: int = 1
-
-    def __post_init__(self):
-        assert self.timestamp > 0 and self.timestamp < (int(datetime.now().timestamp()) + 10)
-
-
 def make_status(stage: str, message: Optional[str] = None, reason: Optional[str] = None):
     status = {
         "stage": stage,

tests/tests_app/core/test_lightning_api.py

@@ -31,6 +31,7 @@
 from lightning_app.runners import MultiProcessRuntime
 from lightning_app.storage.drive import Drive
 from lightning_app.testing.helpers import _MockQueue
+from lightning_app.utilities.app_status import AppStatus
 from lightning_app.utilities.component import _set_frontend_context, _set_work_context
 from lightning_app.utilities.enum import AppStage
 from lightning_app.utilities.load_app import extract_metadata_from_app
@@ -195,7 +196,7 @@ def test_update_publish_state_and_maybe_refresh_ui():
     publish_state_queue = _MockQueue("publish_state_queue")
     api_response_queue = _MockQueue("api_response_queue")
 
-    publish_state_queue.put(app.state_with_changes)
+    publish_state_queue.put((app.state_with_changes, None))
 
     thread = UIRefresher(publish_state_queue, api_response_queue)
     thread.run_once()
@@ -226,7 +227,7 @@ def get(self, timeout: int = 0):
     has_started_queue = _MockQueue("has_started_queue")
     api_response_queue = _MockQueue("api_response_queue")
     state = app.state_with_changes
-    publish_state_queue.put(state)
+    publish_state_queue.put((state, AppStatus(is_ui_ready=True, work_statuses={})))
     spec = extract_metadata_from_app(app)
     ui_refresher = start_server(
         publish_state_queue,
@@ -284,6 +285,9 @@ def get(self, timeout: int = 0):
             {"name": "main_4", "content": "https://te"},
         ]
 
+        response = await client.get("/api/v1/status")
+        assert response.json() == {"is_ui_ready": True, "work_statuses": {}}
+
         response = await client.post("/api/v1/state", json={"state": new_state}, headers=headers)
         assert change_state_queue._queue[1].to_dict() == {
             "values_changed": {"root['vars']['counter']": {"new_value": 1}}

tests/tests_app/core/test_lightning_flow.py

@@ -5,7 +5,7 @@
 from dataclasses import dataclass
 from functools import partial
 from time import time
-from unittest.mock import ANY, MagicMock
+from unittest.mock import ANY
 
 import pytest
 from deepdiff import DeepDiff, Delta
@@ -19,7 +19,7 @@
 from lightning_app.storage.path import _storage_root_dir
 from lightning_app.structures import Dict as LDict
 from lightning_app.structures import List as LList
-from lightning_app.testing.helpers import EmptyFlow, EmptyWork
+from lightning_app.testing.helpers import _MockQueue, EmptyFlow, EmptyWork
 from lightning_app.utilities.app_helpers import (
     _delta_to_app_state_delta,
     _LightningAppRef,
@@ -891,21 +891,37 @@ def run(self):
 
 
 def test_flow_ready():
-    """This test validates the api publish state queue is populated only once ready is True."""
+    """This test validates that the app status queue is populated correctly."""
+
+    mock_queue = _MockQueue("api_publish_state_queue")
 
     def run_patch(method):
-        app.api_publish_state_queue = MagicMock()
-        app.should_publish_changes_to_api = False
+        app.should_publish_changes_to_api = True
+        app.api_publish_state_queue = mock_queue
         method()
 
+    state = {"done": False}
+
+    def lagged_run_once(method):
+        """Ensure that the full loop is run after the app exits."""
+        new_done = method()
+        if state["done"]:
+            return True
+        state["done"] = new_done
+        return False
+
     app = LightningApp(FlowReady())
     app._run = partial(run_patch, method=app._run)
+    app.run_once = partial(lagged_run_once, method=app.run_once)
     MultiProcessRuntime(app, start_server=False).dispatch()
 
-    # Validates the state has been added only when ready was true.
-    state = app.api_publish_state_queue.put._mock_call_args[0][0]
-    call_hash = state["works"]["w"]["calls"]["latest_call_hash"]
-    assert state["works"]["w"]["calls"][call_hash]["statuses"][0]["stage"] == "succeeded"
+    _, first_status = mock_queue.get()
+    assert not first_status.is_ui_ready
+
+    _, last_status = mock_queue.get()
+    while len(mock_queue) > 0:
+        _, last_status = mock_queue.get()
+    assert last_status.is_ui_ready
 
 
 def test_structures_register_work_cloudcompute():