fix: add direct event delivery option but keep polling as default (#7435)

* feat: add new event delivery method "direct"

- Updated event_delivery options in ConfigResponse and Settings to include "direct".
- Modified build_flow function to utilize settings_service for conditional event handling.
- Improved flow processing by returning job_id or event responses based on delivery method.

* feat: implement direct event delivery method on the frontend

- Updated buildFlow function to include eventDelivery parameter, allowing for "direct" event delivery mode.
- Modified NodeStatus and IOModal components to utilize the new eventDelivery setting.
- Expanded flowStore and buildUtils to support event delivery options, improving flexibility in event handling.
- Added "direct" option to event delivery types in enums for better configurability.
- Updated tests to cover new event delivery modes.

* fix: change default event delivery method to "polling"

- Updated the default value of event_delivery in Settings from "direct" to "polling" to align with intended behavior.
- Ensured documentation reflects the change in default settings for clarity on event delivery options.

* Update src/frontend/src/controllers/API/api.tsx

* Update src/frontend/src/utils/buildUtils.ts

* Update src/frontend/src/utils/buildUtils.ts

* Update src/frontend/src/utils/buildUtils.ts

* feat: add event delivery validation for multi-worker environments

- Introduced a new field validator for the `event_delivery` setting to enforce "direct" delivery when the number of workers exceeds one.
- This change ensures compatibility with multi-worker setups, improving the robustness of event handling in the application.

* feat: add warning for multi-worker event delivery

- Added a warning log in the Settings class to notify users when a multi-worker environment is detected, indicating that "direct" event delivery will be used. This enhances visibility and understanding of event handling behavior in such setups.

* refactor: remove "direct" from event delivery modes in tests

- Updated the event delivery modes in the withEventDeliveryModes utility to exclude "direct", aligning with recent changes in event handling behavior.
- This change simplifies the testing setup and ensures consistency with the current application logic.

---------

Co-authored-by: Cristhian Zanforlin Lousa <cristhian.lousa@gmail.com>

src/backend/base/langflow/api/v1/chat.py

@@ -55,10 +55,12 @@ from langflow.services.deps import (
     get_chat_service,
     get_queue_service,
     get_session,
+    get_settings_service,
     get_telemetry_service,
     session_scope,
 )
 from langflow.services.job_queue.service import JobQueueNotFoundError, JobQueueService
+from langflow.services.settings.service import SettingsService
 from langflow.services.telemetry.schema import ComponentPayload, PlaygroundPayload
 
 if TYPE_CHECKING:
@@ -152,6 +154,7 @@ async def build_flow(
     current_user: CurrentActiveUser,
     queue_service: Annotated[JobQueueService, Depends(get_queue_service)],
     flow_name: str | None = None,
+    settings_service: Annotated[SettingsService, Depends(get_settings_service)],
 ):
     """Build and process a flow, returning a job ID for event polling.
 
@@ -170,6 +173,7 @@ async def build_flow(
         current_user: The authenticated user
         queue_service: Queue service for job management
         flow_name: Optional name for the flow
+        settings_service: Settings service
 
     Returns:
         Dict with job_id that can be used to poll for build status
@@ -193,7 +197,13 @@ async def build_flow(
         queue_service=queue_service,
         flow_name=flow_name,
     )
-    return {"job_id": job_id}
+    if settings_service.settings.event_delivery != "direct":
+        return {"job_id": job_id}
+    return await get_flow_events_response(
+        job_id=job_id,
+        queue_service=queue_service,
+        stream=True,
+    )
 
 
 @router.get("/build/{job_id}/events")

src/backend/base/langflow/api/v1/schemas.py

@@ -389,7 +389,7 @@ class ConfigResponse(BaseModel):
     webhook_polling_interval: int
     public_flow_cleanup_interval: int
     public_flow_expiration: int
-    event_delivery: Literal["polling", "streaming"]
+    event_delivery: Literal["polling", "streaming", "direct"]
 
 
 class CancelFlowResponse(BaseModel):

src/backend/base/langflow/services/settings/base.py

@@ -236,12 +236,23 @@ class Settings(BaseSettings):
     public_flow_expiration: int = Field(default=86400, gt=600)
     """The time in seconds after which a public temporary flow will be considered expired and eligible for cleanup.
     Default is 24 hours (86400 seconds). Minimum is 600 seconds (10 minutes)."""
-    event_delivery: Literal["polling", "streaming"] = "polling"
-    """How to deliver build events to the frontend. Can be 'polling' or 'streaming'."""
+    event_delivery: Literal["polling", "streaming", "direct"] = "polling"
+    """How to deliver build events to the frontend. Can be 'polling', 'streaming' or 'direct'."""
     lazy_load_components: bool = False
     """If set to True, Langflow will only partially load components at startup and fully load them on demand.
     This significantly reduces startup time but may cause a slight delay when a component is first used."""
 
+    @field_validator("event_delivery", mode="before")
+    @classmethod
+    def set_event_delivery(cls, value, info):
+        # If workers > 1, we need to use direct delivery
+        # because polling and streaming are not supported
+        # in multi-worker environments
+        if info.data.get("workers", 1) > 1:
+            logger.warning("Multi-worker environment detected, using direct event delivery")
+            return "direct"
+        return value
+
     @field_validator("dev")
     @classmethod
     def set_dev(cls, value):