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(

sgl-model-gateway/src/main.rs

@@ -260,6 +260,10 @@ struct CliArgs {
     #[arg(long, default_value = "info", value_parser = ["debug", "info", "warn", "error"], help_heading = "Logging")]
     log_level: String,
 
+    /// Enable structured JSON log output instead of plain text
+    #[arg(long, default_value_t = false, help_heading = "Logging")]
+    json_log: bool,
+
     // ==================== Prometheus Metrics ====================
     /// Port to expose Prometheus metrics
     #[arg(long, default_value_t = 29000, help_heading = "Prometheus Metrics")]
@@ -1119,6 +1123,7 @@ impl CliArgs {
             max_payload_size: self.max_payload_size,
             log_dir: self.log_dir.clone(),
             log_level: Some(self.log_level.clone()),
+            json_log: self.json_log,
             service_discovery_config,
             prometheus_config,
             request_timeout_secs: self.request_timeout_secs,

sgl-model-gateway/src/server.rs

@@ -533,6 +533,7 @@ pub struct ServerConfig {
     pub max_payload_size: usize,
     pub log_dir: Option<String>,
     pub log_level: Option<String>,
+    pub json_log: bool,
     pub service_discovery_config: Option<ServiceDiscoveryConfig>,
     pub prometheus_config: Option<PrometheusConfig>,
     pub request_timeout_secs: u64,
@@ -722,7 +723,7 @@ pub async fn startup(config: ServerConfig) -> Result<(), Box<dyn std::error::Err
                         }
                     })
                     .unwrap_or(Level::INFO),
-                json_format: false,
+                json_format: config.json_log,
                 log_dir: config.log_dir.clone(),
                 colorize: true,
                 log_file_name: "smg".to_string(),