[router] Health check on worker before adding to the router (#2392)

rust/Cargo.lock

 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "actix-codec"
@@ -2219,6 +2219,7 @@ dependencies = [
  "serde",
  "serde_json",
  "tokenizers",
+ "tokio",
 ]
 
 [[package]]
@@ -2475,9 +2476,9 @@ dependencies = [
 
 [[package]]
 name = "tokio"
-version = "1.41.0"
+version = "1.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "145f3413504347a2be84393cc8a7d2fb4d863b375909ea59f2158261aa258bbb"
+checksum = "5cec9b21b0450273377fc97bd4c33a8acffc8c996c987a7c5b319a0083707551"
 dependencies = [
  "backtrace",
  "bytes",

rust/Cargo.toml

@@ -29,6 +29,7 @@ http = "1.1.0"
 env_logger = "0.11.5"
 log = "0.4.22"
 chrono = "0.4.38"
+tokio = "1.42.0"
 
 [profile.release]
 lto = "thin"

rust/py_test/test_launch_server.py

@@ -20,6 +20,7 @@ def popen_launch_router(
     base_url: str,
     dp_size: int,
     timeout: float,
+    policy: str = "cache_aware",
 ):
     """
     Launch the router server process.
@@ -29,6 +30,7 @@ def popen_launch_router(
         base_url: Server base URL
         dp_size: Data parallel size
         timeout: Server launch timeout
+        policy: Router policy, one of "cache_aware", "round_robin", "random"
     """
     _, host, port = base_url.split(":")
     host = host[2:]
@@ -47,11 +49,10 @@ def popen_launch_router(
         str(dp_size),  # Convert dp_size to string
         "--router-eviction-interval",
         "5",  # frequent eviction for testing
+        "--router-policy",
+        policy,
     ]
 
-    # Use current environment
-    env = None
-
     process = subprocess.Popen(command, stdout=None, stderr=None)
 
     start_time = time.time()
@@ -99,19 +100,8 @@ def popen_launch_server(
 
     process = subprocess.Popen(command, stdout=None, stderr=None)
 
-    start_time = time.time()
-    with requests.Session() as session:
-        while time.time() - start_time < timeout:
-            try:
-                response = session.get(f"{base_url}/health")
-                if response.status_code == 200:
-                    print(f"Server {base_url} is healthy")
-                    return process
-            except requests.RequestException:
-                pass
-            time.sleep(10)
-
-    raise TimeoutError("Server failed to start within the timeout period.")
+    # intentionally don't wait and defer the job to the router health check
+    return process
 
 
 class TestLaunchServer(unittest.TestCase):
@@ -135,6 +125,7 @@ class TestLaunchServer(unittest.TestCase):
             self.base_url,
             dp_size=2,
             timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+            policy="cache_aware",
         )
 
         args = SimpleNamespace(
@@ -160,6 +151,7 @@ class TestLaunchServer(unittest.TestCase):
             self.base_url,
             dp_size=1,
             timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+            policy="round_robin",  # use round robin to make sure every worker processes requests
         )
         # 1. start a worker, and wait until it is healthy
         port = find_available_port()
@@ -168,11 +160,13 @@ class TestLaunchServer(unittest.TestCase):
             self.model, worker_url, DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH
         )
         TestLaunchServer.other_process.append(worker_process)
-        # 2. use /add_worker api to add it the the router
+
+        # 2. use /add_worker api to add it the the router. It will be used by router after it is healthy
         with requests.Session() as session:
             response = session.post(f"{self.base_url}/add_worker?url={worker_url}")
             print(f"status code: {response.status_code}, response: {response.text}")
             self.assertEqual(response.status_code, 200)
+
         # 3. run mmlu
         args = SimpleNamespace(
             base_url=self.base_url,

rust/src/router.rs

@@ -3,13 +3,14 @@ use actix_web::http::header::{HeaderValue, CONTENT_TYPE};
 use actix_web::{HttpRequest, HttpResponse};
 use bytes::Bytes;
 use futures_util::{StreamExt, TryStreamExt};
-use log::{debug, info};
+use log::{debug, info, warn};
 use std::collections::HashMap;
 use std::fmt::Debug;
 use std::sync::atomic::AtomicUsize;
 use std::sync::{Arc, Mutex, RwLock};
 use std::thread;
 use std::time::Duration;
+use tokio;
 
 #[derive(Debug)]
 pub enum Router {
@@ -385,14 +386,66 @@ impl Router {
         }
     }
 
-    pub fn add_worker(&self, worker_url: String) {
-        match self {
-            Router::RoundRobin { worker_urls, .. }
-            | Router::Random { worker_urls }
-            | Router::CacheAware { worker_urls, .. } => {
-                let mut urls = worker_urls.write().unwrap();
-                info!("Added worker: {}", worker_url);
-                urls.push(worker_url);
+    pub async fn add_worker(&self, worker_url: String) -> HttpResponse {
+        let interval_secs = 10; // check every 10 seconds
+        let timeout_secs = 300; // 5 minutes
+
+        let start_time = std::time::Instant::now();
+        let client = reqwest::Client::new();
+
+        loop {
+            if start_time.elapsed() > Duration::from_secs(timeout_secs) {
+                return HttpResponse::InternalServerError().body(format!(
+                    "Timeout {}s waiting for worker {} to become healthy",
+                    timeout_secs, worker_url
+                ));
+            }
+
+            match client.get(&format!("{}/health", worker_url)).send().await {
+                Ok(res) => {
+                    if res.status().is_success() {
+                        match self {
+                            Router::RoundRobin { worker_urls, .. }
+                            | Router::Random { worker_urls }
+                            | Router::CacheAware { worker_urls, .. } => {
+                                info!("Worker {} health check passed", worker_url);
+                                let mut urls = worker_urls.write().unwrap();
+                                if urls.contains(&worker_url) {
+                                    return HttpResponse::BadRequest()
+                                        .body(format!("Worker {} already exists", worker_url));
+                                }
+                                info!("Added worker: {}", worker_url);
+                                urls.push(worker_url.clone());
+                            }
+                        }
+                        return HttpResponse::Ok()
+                            .body(format!("Successfully added worker: {}", worker_url));
+                    } else {
+                        info!(
+                            "Worker {} health check failed with status: {}. The worker might still be starting up.",
+                            worker_url, res.status()
+                        );
+                        // if the url does not have http or https prefix, warn users
+                        if !worker_url.starts_with("http://") && !worker_url.starts_with("https://")
+                        {
+                            warn!("The worker url {} does not have http or https prefix. Please add the prefix to the url.", worker_url);
+                        }
+
+                        tokio::time::sleep(Duration::from_secs(interval_secs)).await;
+                        continue;
+                    }
+                }
+                Err(e) => {
+                    info!("Worker {} health check failed: {}", worker_url, e);
+
+                    // if the url does not have http or https prefix, warn users
+                    if !worker_url.starts_with("http://") && !worker_url.starts_with("https://") {
+                        warn!("The worker url {} does not have http or https prefix. Please add the prefix to the url.", worker_url);
+                    }
+
+                    tokio::time::sleep(Duration::from_secs(interval_secs)).await;
+                    continue;
+                }
             }
         }
     }

rust/src/server.rs

@@ -141,8 +141,7 @@ async fn add_worker(
                 .body("Worker URL required. Provide 'url' query parameter")
         }
     };
-    data.router.add_worker(worker_url);
-    HttpResponse::Ok().finish()
+    data.router.add_worker(worker_url).await
 }
 
 #[post("/remove_worker")]