feat(trace): support SGLANG_TRACE_LEVEL env var for startup trace level (#24716)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/references/production_request_trace.md

@@ -52,9 +52,14 @@ This section explains how to configure the request tracing and export the trace
     0: disable tracing
     1: Trace important slices
     2: Trace all slices except nested ones
-    3: Trace all slices
+    3: Trace all slices (default)
     ```
-    The trace level can be dynamically set via HTTP API, for example:
+    **At startup** — set `SGLANG_TRACE_LEVEL` before launching the server:
+    ```bash
+    SGLANG_TRACE_LEVEL=2 python -m sglang.launch_server --enable-trace --otlp-traces-endpoint 0.0.0.0:4317 <other options>
+    ```
+
+    **At runtime** — dynamically adjust via HTTP API without restarting:
     ```bash
     curl http://0.0.0.0:30000/set_trace_level?level=2
     ```

python/sglang/srt/observability/trace.py

@@ -32,7 +32,7 @@ opentelemetry_initialized = False
 _trace_context_propagator = None
 tracer: Optional[trace.Tracer] = None
 
-global_trace_level = 3
+global_trace_level = get_int_env_var("SGLANG_TRACE_LEVEL", 3)
 
 TRACE_HEADERS = ["traceparent", "tracestate"]
 

test/registered/unit/observability/test_trace.py

@@ -56,6 +56,15 @@ class TestTraceFunctions(unittest.TestCase):
         self.assertEqual(mod.global_trace_level, 5)
         mod.global_trace_level = orig
 
+    def test_global_trace_level_env_var(self):
+        import importlib
+
+        with patch.dict(os.environ, {"SGLANG_TRACE_LEVEL": "2"}):
+            importlib.reload(mod)
+            self.assertEqual(mod.global_trace_level, 2)
+        importlib.reload(mod)  # restore default (SGLANG_TRACE_LEVEL unset → 3)
+        self.assertEqual(mod.global_trace_level, 3)
+
     def test_get_global_tracing_enabled(self):
         self.assertEqual(get_global_tracing_enabled(), mod.opentelemetry_initialized)