[router] add metrics for worker and policy (#8971)

Signed-off-by: Tony Lu <tonyluj@gmail.com>

sgl-router/src/core/worker.rs

 use super::{CircuitBreaker, CircuitBreakerConfig, WorkerError, WorkerResult};
+use crate::metrics::RouterMetrics;
 use async_trait::async_trait;
 use futures;
 use serde_json;
@@ -259,6 +260,7 @@ impl Worker for BasicWorker {
 
     fn set_healthy(&self, healthy: bool) {
         self.healthy.store(healthy, Ordering::Release);
+        RouterMetrics::set_worker_health(self.url(), healthy);
     }
 
     async fn check_health_async(&self) -> WorkerResult<()> {

sgl-router/src/policies/cache_aware.rs

@@ -181,6 +181,7 @@ impl LoadBalancingPolicy for CacheAwarePolicy {
             // Increment processed counter
             workers[min_load_idx].increment_processed();
             RouterMetrics::record_processed_request(workers[min_load_idx].url());
+            RouterMetrics::record_policy_decision(self.name(), workers[min_load_idx].url());
 
             return Some(min_load_idx);
         }

sgl-router/src/policies/power_of_two.rs

@@ -90,6 +90,7 @@ impl LoadBalancingPolicy for PowerOfTwoPolicy {
         // Increment processed counter
         workers[selected_idx].increment_processed();
         RouterMetrics::record_processed_request(workers[selected_idx].url());
+        RouterMetrics::record_policy_decision(self.name(), workers[selected_idx].url());
 
         Some(selected_idx)
     }

sgl-router/src/policies/random.rs

@@ -2,6 +2,7 @@
 
 use super::{get_healthy_worker_indices, LoadBalancingPolicy};
 use crate::core::Worker;
+use crate::metrics::RouterMetrics;
 use rand::Rng;
 
 /// Random selection policy
@@ -30,6 +31,10 @@ impl LoadBalancingPolicy for RandomPolicy {
 
         let mut rng = rand::thread_rng();
         let random_idx = rng.gen_range(0..healthy_indices.len());
+        let worker = workers[healthy_indices[random_idx]].url();
+
+        RouterMetrics::record_processed_request(worker);
+        RouterMetrics::record_policy_decision(self.name(), worker);
         Some(healthy_indices[random_idx])
     }
 

sgl-router/src/policies/round_robin.rs

@@ -2,6 +2,7 @@
 
 use super::{get_healthy_worker_indices, LoadBalancingPolicy};
 use crate::core::Worker;
+use crate::metrics::RouterMetrics;
 use std::sync::atomic::{AtomicUsize, Ordering};
 
 /// Round-robin selection policy
@@ -35,7 +36,10 @@ impl LoadBalancingPolicy for RoundRobinPolicy {
         // Get and increment counter atomically
         let count = self.counter.fetch_add(1, Ordering::Relaxed);
         let selected_idx = count % healthy_indices.len();
+        let worker = workers[healthy_indices[selected_idx]].url();
 
+        RouterMetrics::record_processed_request(worker);
+        RouterMetrics::record_policy_decision(self.name(), worker);
         Some(healthy_indices[selected_idx])
     }