Add --json-log flag to enable structured JSON logging (#19968)

Co-authored-by: github_username <github_email>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sgl-model-gateway/bindings/python/src/lib.rs

@@ -354,6 +354,7 @@ struct Router {
     api_key: Option<String>,
     log_dir: Option<String>,
     log_level: Option<String>,
+    json_log: bool,
     service_discovery: bool,
     selector: HashMap<String, String>,
     service_discovery_port: u16,
@@ -657,6 +658,7 @@ impl Router {
         api_key = None,
         log_dir = None,
         log_level = None,
+        json_log = false,
         service_discovery = false,
         selector = HashMap::new(),
         service_discovery_port = 80,
@@ -743,6 +745,7 @@ impl Router {
         api_key: Option<String>,
         log_dir: Option<String>,
         log_level: Option<String>,
+        json_log: bool,
         service_discovery: bool,
         selector: HashMap<String, String>,
         service_discovery_port: u16,
@@ -842,6 +845,7 @@ impl Router {
             api_key,
             log_dir,
             log_level,
+            json_log,
             service_discovery,
             selector,
             service_discovery_port,
@@ -963,6 +967,7 @@ impl Router {
                 max_payload_size: self.max_payload_size,
                 log_dir: self.log_dir.clone(),
                 log_level: self.log_level.clone(),
+                json_log: self.json_log,
                 service_discovery_config,
                 prometheus_config,
                 request_timeout_secs: self.request_timeout_secs,

sgl-model-gateway/bindings/python/src/sglang_router/router_args.py

@@ -45,6 +45,7 @@ class RouterArgs:
     api_key: Optional[str] = None
     log_dir: Optional[str] = None
     log_level: Optional[str] = None
+    json_log: bool = False
     # Service discovery configuration
     service_discovery: bool = False
     selector: Dict[str, str] = dataclasses.field(default_factory=dict)
@@ -413,6 +414,11 @@ class RouterArgs:
             choices=["debug", "info", "warn", "error"],
             help="Set the logging level. If not specified, defaults to INFO.",
         )
+        logging_group.add_argument(
+            f"--{prefix}json-log",
+            action="store_true",
+            help="Enable structured JSON log output instead of plain text.",
+        )
 
         # Service discovery configuration
         k8s_group.add_argument(