feat: Add per-worker Prometheus metrics for router load monitoring (#5842)

Signed-off-by: hongkuanz <hongkuanz@nvidia.com>

lib/llm/src/protocols/openai/nvext.rs

@@ -75,9 +75,17 @@ pub struct WorkerIdInfo {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub prefill_worker_id: Option<u64>,
 
+    /// The prefill worker's data parallel rank
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub prefill_dp_rank: Option<u32>,
+
     /// The decode worker ID that processed this request
     #[serde(skip_serializing_if = "Option::is_none")]
     pub decode_worker_id: Option<u64>,
+
+    /// The decode worker's data parallel rank
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub decode_dp_rank: Option<u32>,
 }
 
 /// NVIDIA LLM response extensions

lib/runtime/src/metrics/prometheus_names.rs

@@ -150,6 +150,29 @@ pub mod frontend_service {
     /// Total number of request migrations due to worker unavailability
     pub const MODEL_MIGRATION_TOTAL: &str = "model_migration_total";
 
+    /// Active decode blocks (KV cache blocks) per worker
+    /// Gauge metric tracking current KV cache block utilization for each worker
+    pub const WORKER_ACTIVE_DECODE_BLOCKS: &str = "worker_active_decode_blocks";
+
+    /// Active prefill tokens per worker
+    /// Gauge metric tracking current queued prefill tokens for each worker
+    pub const WORKER_ACTIVE_PREFILL_TOKENS: &str = "worker_active_prefill_tokens";
+
+    /// Last observed time to first token per worker (in seconds)
+    /// Gauge metric tracking the most recent TTFT for each worker
+    pub const WORKER_LAST_TIME_TO_FIRST_TOKEN_SECONDS: &str =
+        "worker_last_time_to_first_token_seconds";
+
+    /// Last observed input sequence tokens per worker
+    /// Gauge metric tracking the input token count from the same request as WORKER_LAST_TIME_TO_FIRST_TOKEN_SECONDS
+    /// Updated atomically with TTFT to correlate latency with input size
+    pub const WORKER_LAST_INPUT_SEQUENCE_TOKENS: &str = "worker_last_input_sequence_tokens";
+
+    /// Last observed inter-token latency per worker (in seconds)
+    /// Gauge metric tracking the most recent ITL for each worker
+    pub const WORKER_LAST_INTER_TOKEN_LATENCY_SECONDS: &str =
+        "worker_last_inter_token_latency_seconds";
+
     /// Label name for the type of migration
     pub const MIGRATION_TYPE_LABEL: &str = "migration_type";