fix: use configured backend_host in notify_backend() instead of hardcoded 0.0.0.0

The notify_backend() function was hardcoding "0.0.0.0" as the backend
host in the terminal log output, ignoring the backend_host value set in
rxconfig.py or passed via --backend-host CLI argument.

This change:
- Adds an optional `host` parameter to notify_backend() that falls back
  to config.backend_host when not provided
- Passes the resolved host from run_backend() and run_backend_prod()
  call sites so CLI --backend-host overrides are reflected in logs
- Persists the resolved backend_host in the config (via _set_persistent)
  so it is available to notify_backend() even when called from the
  frontend thread in run_process_and_launch_url()

Fixes #6165

Author: Krishnachaitanyakc

reflex/reflex.py

@@ -198,11 +198,13 @@ def _run(
             auto_increment=auto_increment_backend,
         )
 
-    # Apply the new ports to the config.
+    # Apply the new ports and host to the config.
     if frontend_port != config.frontend_port:
         config._set_persistent(frontend_port=frontend_port)
     if backend_port != config.backend_port:
         config._set_persistent(backend_port=backend_port)
+    if backend_host != config.backend_host:
+        config._set_persistent(backend_host=backend_host)
 
     # Reload the config to make sure the env vars are persistent.
     get_config(reload=True)

reflex/utils/exec.py

@@ -157,10 +157,16 @@ def notify_frontend(url: str, backend_present: bool):
     )
 
 
-def notify_backend():
-    """Output a string notifying where the backend is running."""
+def notify_backend(host: str | None = None):
+    """Output a string notifying where the backend is running.
+
+    Args:
+        host: The backend host. If not provided, falls back to the config value.
+    """
+    config = get_config()
+    effective_host = host or config.backend_host
     console.print(
-        f"Backend running at: [bold green]http://0.0.0.0:{get_config().backend_port}[/bold green]"
+        f"Backend running at: [bold green]http://{effective_host}:{config.backend_port}[/bold green]"
     )
 
 
@@ -378,7 +384,7 @@ def run_backend(
         (web_dir / constants.NOCOMPILE_FILE).touch()
 
     if not frontend_present:
-        notify_backend()
+        notify_backend(host)
 
     # Run the backend in development mode.
     if should_use_granian():
@@ -579,7 +585,7 @@ def run_backend_prod(
         mount_frontend_compiled_app: Whether to mount the compiled frontend app with the backend.
     """
     if not frontend_present:
-        notify_backend()
+        notify_backend(host)
 
     environment.REFLEX_MOUNT_FRONTEND_COMPILED_APP.set(mount_frontend_compiled_app)