[Bug fix] trace: fix import error in mini_lb if sgl-router image does not install sglang (#12338)

sgl-router/py_src/sglang_router/launch_router.py

@@ -38,15 +38,6 @@ def launch_router(args: argparse.Namespace) -> Optional[Router]:
             router_args = args
 
         if router_args.mini_lb:
-            if router_args.enable_trace:
-                from sglang.srt.tracing.trace import (
-                    process_tracing_init,
-                    trace_set_thread_info,
-                )
-
-                process_tracing_init(router_args.otlp_traces_endpoint, "sglang")
-                trace_set_thread_info("Mini lb")
-
             mini_lb = MiniLoadBalancer(router_args)
             mini_lb.start()
         else:

sgl-router/py_src/sglang_router/mini_lb.py

@@ -18,13 +18,20 @@ from fastapi import FastAPI, HTTPException
 from fastapi.responses import ORJSONResponse, Response, StreamingResponse
 from sglang_router.router_args import RouterArgs
 
-from sglang.srt.tracing.trace import (
-    trace_get_remote_propagate_context,
-    trace_req_finish,
-    trace_req_start,
-    trace_slice_end,
-    trace_slice_start,
-)
+try:
+    from sglang.srt.tracing.trace import (
+        process_tracing_init,
+        trace_get_remote_propagate_context,
+        trace_req_finish,
+        trace_req_start,
+        trace_set_thread_info,
+        trace_slice_end,
+        trace_slice_start,
+    )
+
+    trace_package_imported = True
+except ImportError:
+    trace_package_imported = False
 
 logger = logging.getLogger(__name__)
 
@@ -54,7 +61,13 @@ class MiniLoadBalancer:
         self.prefill_urls = [url[0] for url in router_args.prefill_urls]
         self.prefill_bootstrap_ports = [url[1] for url in router_args.prefill_urls]
         self.decode_urls = router_args.decode_urls
+        self.otlp_traces_endpoint = router_args.otlp_traces_endpoint
         self.enable_trace = router_args.enable_trace
+        if self.enable_trace and not trace_package_imported:
+            logger.warning(
+                "Tracing is not supported in this environment. Please install sglang."
+            )
+            self.enable_trace = False
 
     def _validate_router_args(self, router_args: RouterArgs):
         logger.warning(
@@ -77,6 +90,9 @@ class MiniLoadBalancer:
     def start(self):
         global lb
         lb = self
+        if self.enable_trace:
+            process_tracing_init(self.otlp_traces_endpoint, "sglang")
+            trace_set_thread_info("Mini lb")
         uvicorn.run(app, host=self.host, port=self.port)
 
     def select_pair(self):
@@ -441,8 +457,9 @@ async def handle_completion_request(request_data: dict):
 
 def _generate_bootstrap_room():
     bootstrap_room = random.randint(0, 2**63 - 1)
-    trace_req_start(bootstrap_room, bootstrap_room, role="router")
-    trace_slice_start("mini_lb_launch", bootstrap_room)
+    if lb.enable_trace:
+        trace_req_start(bootstrap_room, bootstrap_room, role="router")
+        trace_slice_start("mini_lb_launch", bootstrap_room)
     return bootstrap_room