[sgl-router] Fix readiness, IPv6 discovery, logging, and model validation (#40604)

experimental/sgl-router/src/discovery/k8s.rs

@@ -118,7 +118,12 @@ fn extract_workers(es: &EndpointSlice, mode: WorkerMode) -> Vec<WorkerSpec> {
         }
         let pod_uid: Option<&str> = ep.target_ref.as_ref().and_then(|r| r.uid.as_deref());
         for addr in &ep.addresses {
-            let url = format!("http://{addr}:{port}");
+            let host = if es.address_type == "IPv6" {
+                format!("[{addr}]")
+            } else {
+                addr.clone()
+            };
+            let url = format!("http://{host}:{port}");
             let id = match pod_uid {
                 Some(uid) => WorkerId(format!("{ns}/{uid}")),
                 None => WorkerId(format!("{ns}/{slice_name}/{addr}:{port}")),
@@ -541,6 +546,15 @@ mod tests {
         assert_eq!(ws[0].mode, WorkerMode::Decode);
     }
 
+    #[test]
+    fn brackets_ipv6_worker_addresses() {
+        let mut slice = make_slice(&["2001:db8::1"], 30000, true);
+        slice.address_type = "IPv6".into();
+        let workers = extract_workers(&slice, WorkerMode::Plain);
+        assert_eq!(workers[0].url, "http://[2001:db8::1]:30000");
+        assert!(url::Url::parse(&workers[0].url).is_ok());
+    }
+
     #[test]
     fn skips_not_ready_endpoints() {
         let s = make_slice(&["10.0.0.1"], 30000, false);

experimental/sgl-router/src/main.rs

@@ -50,14 +50,10 @@ const DRAIN_WARN_AFTER: Duration = Duration::from_secs(30);
 async fn main() -> Result<()> {
     // Resolve CLI configuration and set up startup logging.
     let cli = Cli::parse();
-    install_bootstrap_subscriber();
+    init_tracing(&cli.server.log_level, cli.server.log_format)?;
     let config = cli
         .into_config()
         .context("resolve configuration from CLI flags")?;
-    init_tracing(
-        &config.observability.log_level,
-        config.observability.log_format,
-    )?;
 
     // Buffer termination signals before tokenizer loading or discovery can block startup.
     let (sigterm, sigint) = install_signal_handlers()?;
@@ -150,16 +146,6 @@ fn init_tracing(default_level: &str, format: LogFormat) -> Result<()> {
     Ok(())
 }
 
-// Provide startup logging before configuration resolution; later installs are no-ops.
-fn install_bootstrap_subscriber() {
-    let filter = tracing_subscriber::EnvFilter::try_from_default_env()
-        .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info"));
-    let _ = tracing_subscriber::fmt()
-        .with_env_filter(filter)
-        .with_target(true)
-        .try_init();
-}
-
 fn install_signal_handlers() -> Result<(Signal, Signal)> {
     let sigterm = signal(SignalKind::terminate()).context("install SIGTERM handler")?;
     let sigint = signal(SignalKind::interrupt()).context("install SIGINT handler")?;

experimental/sgl-router/src/server/routes/chat.rs

@@ -62,15 +62,16 @@ async fn chat_completions_legacy(
             .ok_or_else(|| ApiError::BadRequest("missing `model` field".into()))?,
     );
 
+    let policy = ctx
+        .policies
+        .get(&model)
+        .ok_or_else(|| ApiError::ModelNotFound(model.0.clone()))?;
+
     // Find healthy workers: the prefill pool in PD mode, otherwise the plain pool.
     let resolver = PdPoolResolver::new(Arc::clone(&ctx.registry));
     let candidates = resolver
         .prefill_candidates(&model)
         .map_err(|error| pool_error(error, &model))?;
-    let policy = ctx
-        .policies
-        .get(&model)
-        .ok_or_else(|| ApiError::ModelNotFound(model.0.clone()))?;
 
     let request =
         PreparedChatRequest::prepare(ctx, model, fields, body, policy.needs_request_tokens())?;

experimental/sgl-router/src/server/routes/health.rs

@@ -1,6 +1,8 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026 The SGLang Authors
 // SPDX-License-Identifier: Apache-2.0
 
+use crate::discovery::ModelId;
+use crate::policies::registry::{PdPoolResolver, PdPools};
 use crate::server::app_context::AppContext;
 use axum::extract::State;
 use axum::http::StatusCode;
@@ -11,18 +13,18 @@ pub async fn healthz() -> StatusCode {
     StatusCode::OK
 }
 
-/// Readiness probe — 200 only when the pod can actually serve traffic.
+/// Ready after startup only when the configured model has a usable plain or PD pool.
-///
-/// Requires BOTH:
-/// 1. `AppContext::mark_ready()` was called by main (process bootstrap
-///    finished — config loaded, tokenizers built, server bound), AND
-/// 2. At least one worker is registered. Without this second check,
-///    `/readyz` flips green before the first `DiscoveryEvent::Added`
-///    has been processed — the Service starts sending traffic to a
-///    pod whose registry is empty, and every request returns 503
-///    `no_healthy_workers`.
 pub async fn readyz(State(ctx): State<Arc<AppContext>>) -> StatusCode {
-    if ctx.is_ready() && !ctx.registry.is_empty() {
+    if !ctx.is_ready() {
+        return StatusCode::SERVICE_UNAVAILABLE;
+    }
+    let resolver = PdPoolResolver::new(Arc::clone(&ctx.registry));
+    let ready = match resolver.resolve(&ModelId(ctx.config.model.id.clone())) {
+        Ok(PdPools::Plain { workers }) => !workers.is_empty(),
+        Ok(PdPools::Pd { prefill, decode }) => !prefill.is_empty() && !decode.is_empty(),
+        Err(_) => false,
+    };
+    if ready {
         StatusCode::OK
     } else {
         StatusCode::SERVICE_UNAVAILABLE
@@ -104,6 +106,35 @@ mod tests {
         assert_eq!(res.status(), StatusCode::OK);
     }
 
+    #[tokio::test]
+    async fn readiness_requires_resolved_model_and_both_pd_roles() {
+        use crate::discovery::{WorkerId, WorkerMode, WorkerSpec};
+
+        use WorkerMode::{Decode, Plain, Prefill};
+
+        for (model, modes, ready) in [
+            (None, vec![Plain], false),
+            (Some("other"), vec![Plain], false),
+            (Some("stub-model"), vec![Prefill], false),
+            (Some("stub-model"), vec![Decode], false),
+            (Some("stub-model"), vec![Prefill, Decode], true),
+        ] {
+            let ctx = test_ctx(true, false);
+            for (i, mode) in modes.into_iter().enumerate() {
+                ctx.registry
+                    .add(WorkerSpec {
+                        id: WorkerId(i.to_string()),
+                        url: format!("http://worker-{i}:30000"),
+                        mode,
+                        model_ids: model.map(|m| ModelId(m.into())).into_iter().collect(),
+                        bootstrap_port: None,
+                    })
+                    .unwrap();
+            }
+            assert_eq!(readyz(State(ctx)).await == StatusCode::OK, ready);
+        }
+    }
+
     fn test_ctx(ready: bool, with_worker: bool) -> Arc<AppContext> {
         use crate::discovery::{ModelId, WorkerId, WorkerMode, WorkerSpec};
         let ctx = AppContext::stub();
@@ -116,7 +147,7 @@ mod tests {
                     id: WorkerId("test-w".into()),
                     url: "http://test:30000".into(),
                     mode: WorkerMode::Plain,
-                    model_ids: vec![ModelId("test".into())],
+                    model_ids: vec![ModelId(ctx.config.model.id.clone())],
                     bootstrap_port: None,
                 })
                 .expect("test worker accepted");

experimental/sgl-router/tests/proxy/chat_routing.rs

@@ -939,6 +939,21 @@ async fn no_healthy_workers_returns_503() {
     );
 }
 
+#[tokio::test]
+async fn unknown_model_without_workers_returns_404() {
+    let ctx = build_ctx_with_worker("http://127.0.0.1:1");
+    ctx.registry.remove(&WorkerId("w1".into()));
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/chat/completions")
+        .header("content-type", "application/json")
+        .body(Body::from(r#"{"model":"unknown","messages":[]}"#))
+        .unwrap();
+    let response = build_router(ctx).oneshot(request).await.unwrap();
+    assert_eq!(response.status(), StatusCode::NOT_FOUND);
+    assert_eq!(response.headers()["x-router-error-code"], "model_not_found");
+}
+
 /// A worker is registered for a model that is NOT the configured `cfg.model` (so the
 /// policy registry has no entry for it).  The handler returns 404
 /// `model_not_found` rather than 500 — clients can recover by sending a