feat(dynamo-run): Basic routing choice (#524)

As a first step towards KV routing:
- introduce a `--router-mode` in dynamo-run that only does random and round-robin right now. Not that interesting yet.
- Make the vllm engine publish the KV events received from our patched vllm.

Now we "just" need to connect the two. Easy right?

launch/dynamo-run/src/flags.rs

@@ -17,6 +17,9 @@ use std::collections::HashMap;
 use std::path::PathBuf;
 use std::str::FromStr;
 
+use clap::ValueEnum;
+use dynamo_runtime::component::RouterMode as RuntimeRouterMode;
+
 /// Required options depend on the in and out choices
 #[derive(clap::Parser, Debug, Clone)]
 #[command(version, about, long_about = None)]
@@ -92,6 +95,13 @@ pub struct Flags {
     #[arg(long)]
     pub leader_addr: Option<String>,
 
+    /// If using `out=dyn://..` with multiple backends, this says how to route the requests.
+    ///
+    /// Mostly interesting for KV-aware routing.
+    /// Defaults to RouterMode::Random
+    #[arg(long, default_value = "random")]
+    pub router_mode: RouterMode,
+
     /// Internal use only.
     // Start the python vllm engine sub-process.
     #[arg(long, hide = true, default_value = "false")]
@@ -198,3 +208,29 @@ fn parse_sglang_flags(s: &str) -> Result<SgLangFlags, String> {
         gpu_id: nums[2],
     })
 }
+
+#[derive(Default, PartialEq, Eq, ValueEnum, Clone, Debug)]
+pub enum RouterMode {
+    #[default]
+    Random,
+    #[value(name = "round-robin")]
+    RoundRobin,
+    #[value(name = "kv")]
+    KV,
+}
+
+impl RouterMode {
+    pub fn is_kv_routing(&self) -> bool {
+        *self == RouterMode::KV
+    }
+}
+
+impl From<RouterMode> for RuntimeRouterMode {
+    fn from(r: RouterMode) -> RuntimeRouterMode {
+        match r {
+            RouterMode::RoundRobin => RuntimeRouterMode::RoundRobin,
+            RouterMode::KV => todo!("KV not implemented yet"),
+            _ => RuntimeRouterMode::Random,
+        }
+    }
+}

launch/dynamo-run/src/input/batch.rs

@@ -31,7 +31,7 @@ use std::time::{Duration, Instant};
 use tokio::io::{AsyncBufReadExt, AsyncWriteExt};
 
 use crate::input::common;
-use crate::EngineConfig;
+use crate::{EngineConfig, Flags};
 
 /// Max tokens in each response.
 /// TODO: For batch mode this should be the full context size of the model
@@ -64,11 +64,12 @@ struct Entry {
 
 pub async fn run(
     runtime: Runtime,
-    cancel_token: CancellationToken,
+    flags: Flags,
     maybe_card: Option<ModelDeploymentCard>,
     input_jsonl: PathBuf,
     engine_config: EngineConfig,
 ) -> anyhow::Result<()> {
+    let cancel_token = runtime.primary_token();
     // Check if the path exists and is a directory
     if !input_jsonl.exists() || !input_jsonl.is_file() {
         anyhow::bail!(
@@ -78,7 +79,7 @@ pub async fn run(
     }
 
     let (service_name, engine, _inspect_template) =
-        common::prepare_engine(runtime.clone(), engine_config).await?;
+        common::prepare_engine(runtime, flags, engine_config).await?;
     let service_name_ref = Arc::new(service_name);
 
     let pre_processor = if let Some(card) = maybe_card {

launch/dynamo-run/src/input/common.rs

@@ -13,7 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::EngineConfig;
+use crate::{flags::RouterMode, EngineConfig, Flags};
 use dynamo_llm::{
     backend::Backend,
     preprocessor::OpenAIPreprocessor,
@@ -34,6 +34,7 @@ use std::sync::Arc;
 /// Turns an EngineConfig into an OpenAIChatCompletionsStreamingEngine.
 pub async fn prepare_engine(
     runtime: Runtime,
+    flags: Flags,
     engine_config: EngineConfig,
 ) -> anyhow::Result<(String, OpenAIChatCompletionsStreamingEngine, bool)> {
     match engine_config {
@@ -41,14 +42,21 @@ pub async fn prepare_engine(
             let distributed_runtime = DistributedRuntime::from_settings(runtime.clone()).await?;
 
             let endpoint = distributed_runtime
-                .namespace(endpoint_id.namespace)?
-                .component(endpoint_id.component)?
-                .endpoint(endpoint_id.name);
+                .namespace(endpoint_id.namespace.clone())?
+                .component(endpoint_id.component.clone())?
+                .endpoint(endpoint_id.name.clone());
 
-            let client = endpoint.client::<NvCreateChatCompletionRequest, Annotated<NvCreateChatCompletionStreamResponse>>().await?;
+            let mut client = endpoint.client::<NvCreateChatCompletionRequest, Annotated<NvCreateChatCompletionStreamResponse>>().await?;
+
+            match &flags.router_mode {
+                RouterMode::Random | RouterMode::RoundRobin => {
+                    client.set_router_mode(flags.router_mode.into());
                     tracing::info!("Waiting for remote model..");
                     client.wait_for_endpoints().await?;
                     tracing::info!("Model discovered");
+                }
+                RouterMode::KV => todo!(),
+            }
 
             // The service_name isn't used for text chat outside of logs,
             // so use the path. That avoids having to listen on etcd for model registration.

launch/dynamo-run/src/input/endpoint.rs

@@ -28,21 +28,22 @@ use dynamo_llm::{
 use dynamo_runtime::pipeline::{
     network::Ingress, ManyOut, Operator, SegmentSource, ServiceBackend, SingleIn, Source,
 };
-use dynamo_runtime::{protocols::Endpoint, DistributedRuntime, Runtime};
+use dynamo_runtime::{protocols::Endpoint, DistributedRuntime};
 
 use crate::EngineConfig;
 
 pub async fn run(
-    runtime: Runtime,
+    distributed_runtime: DistributedRuntime,
     path: String,
     engine_config: EngineConfig,
 ) -> anyhow::Result<()> {
     // This will attempt to connect to NATS and etcd
-    let distributed = DistributedRuntime::from_settings(runtime.clone()).await?;
 
-    let cancel_token = runtime.primary_token().clone();
+    let cancel_token = distributed_runtime.primary_token().clone();
     let endpoint_id: Endpoint = path.parse()?;
 
+    let etcd_client = distributed_runtime.etcd_client();
+
     let (ingress, service_name) = match engine_config {
         EngineConfig::StaticFull {
             service_name,
@@ -85,7 +86,7 @@ pub async fn run(
         model_type: ModelType::Chat,
     };
 
-    let component = distributed
+    let component = distributed_runtime
         .namespace(endpoint_id.namespace)?
         .component(endpoint_id.component)?;
     let endpoint = component
@@ -94,8 +95,8 @@ pub async fn run(
         .await?
         .endpoint(endpoint_id.name);
 
-    if let Some(etcd_client) = distributed.etcd_client() {
-        let network_name = endpoint.subject();
+    if let Some(etcd_client) = etcd_client {
+        let network_name = endpoint.subject_to(etcd_client.lease_id());
         tracing::debug!("Registering with etcd as {network_name}");
         etcd_client
             .kv_create(

launch/dynamo-run/src/input/http.rs

@@ -32,16 +32,16 @@ use dynamo_runtime::{
     DistributedRuntime, Runtime,
 };
 
-use crate::EngineConfig;
+use crate::{EngineConfig, Flags};
 
 /// Build and run an HTTP service
 pub async fn run(
     runtime: Runtime,
-    http_port: u16,
+    flags: Flags,
     engine_config: EngineConfig,
 ) -> anyhow::Result<()> {
     let http_service = service_v2::HttpService::builder()
-        .port(http_port)
+        .port(flags.http_port)
         .enable_chat_endpoints(true)
         .enable_cmpl_endpoints(true)
         .build()?;

launch/dynamo-run/src/input/text.rs

@@ -21,7 +21,7 @@ use futures::StreamExt;
 use std::io::{ErrorKind, Write};
 
 use crate::input::common;
-use crate::EngineConfig;
+use crate::{EngineConfig, Flags};
 
 /// Max response tokens for each single query. Must be less than model context size.
 /// TODO: Cmd line flag to overwrite this
@@ -29,15 +29,16 @@ const MAX_TOKENS: u32 = 8192;
 
 pub async fn run(
     runtime: Runtime,
-    cancel_token: CancellationToken,
+    flags: Flags,
     single_prompt: Option<String>,
     engine_config: EngineConfig,
 ) -> anyhow::Result<()> {
+    let cancel_token = runtime.primary_token();
     let (service_name, engine, inspect_template): (
         String,
         OpenAIChatCompletionsStreamingEngine,
         bool,
-    ) = common::prepare_engine(runtime.clone(), engine_config).await?;
+    ) = common::prepare_engine(runtime, flags, engine_config).await?;
     main_loop(
         cancel_token,
         &service_name,

launch/dynamo-run/src/lib.rs

@@ -13,15 +13,16 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use std::io::Read;
 #[cfg(any(feature = "vllm", feature = "sglang"))]
 use std::{future::Future, pin::Pin};
+use std::{io::Read, sync::Arc};
 
 use dynamo_llm::{
-    backend::ExecutionContext, model_card::model::ModelDeploymentCard,
+    backend::ExecutionContext, kv_router::publisher::KvMetricsPublisher,
+    model_card::model::ModelDeploymentCard,
     types::openai::chat_completions::OpenAIChatCompletionsStreamingEngine,
 };
-use dynamo_runtime::protocols::Endpoint;
+use dynamo_runtime::{protocols::Endpoint, DistributedRuntime};
 
 mod flags;
 pub use flags::Flags;
@@ -41,6 +42,9 @@ const ENDPOINT_SCHEME: &str = "dyn://";
 /// the command line. Hence it's optional, and defaults to this.
 const INVISIBLE_MODEL_NAME: &str = "dynamo-run";
 
+/// The component name for the KV publisher, if used
+const KV_PUBLISHER_COMPONENT: &str = "kvpublisher";
+
 /// How we identify a python string endpoint
 #[cfg(feature = "python")]
 const PYTHON_STR_SCHEME: &str = "pystr:";
@@ -70,6 +74,12 @@ pub enum EngineConfig {
     None,
 }
 
+/// Distributed system values
+struct DynInput {
+    endpoint_id: Endpoint,
+    distributed_runtime: DistributedRuntime,
+}
+
 #[allow(unused_mut)]
 pub async fn run(
     runtime: dynamo_runtime::Runtime,
@@ -171,6 +181,19 @@ pub async fn run(
         }
     };
 
+    // If we are in a distributed system, we need to know our component upfront
+    let dyn_input = match &in_opt {
+        Input::Endpoint(endpoint_path) => {
+            let distributed_runtime = DistributedRuntime::from_settings(runtime.clone()).await?;
+            let endpoint_id: Endpoint = endpoint_path.parse()?;
+            Some(DynInput {
+                endpoint_id,
+                distributed_runtime,
+            })
+        }
+        _ => None,
+    };
+
     #[cfg(any(feature = "vllm", feature = "sglang"))]
     let mut extra: Option<Pin<Box<dyn Future<Output = ()> + Send>>> = None; // vllm and sglang sub-process
 
@@ -219,7 +242,6 @@ pub async fn run(
         }
         #[cfg(feature = "sglang")]
         Output::SgLang => {
-            use dynamo_engine_sglang;
             let Some(model_path) = model_path else {
                 anyhow::bail!("out=sglang requires flag --model-path=<full-path-to-model-dir>");
             };
@@ -234,7 +256,7 @@ pub async fn run(
             let node_conf = dynamo_llm::engines::MultiNodeConfig {
                 num_nodes: flags.num_nodes,
                 node_rank: flags.node_rank,
-                leader_addr: flags.leader_addr.unwrap_or_default(),
+                leader_addr: flags.leader_addr.clone().unwrap_or_default(),
             };
             if node_conf.num_nodes > 1 {
                 if let Ok(Some(if_name)) = net::get_primary_interface().await {
@@ -256,7 +278,7 @@ pub async fn run(
                 node_conf,
                 flags.tensor_parallel_size,
                 flags.base_gpu_id,
-                flags.extra_engine_args,
+                flags.extra_engine_args.clone(),
             )
             .await?;
             extra = Some(Box::pin(async move {
@@ -289,7 +311,7 @@ pub async fn run(
             let node_conf = dynamo_llm::engines::MultiNodeConfig {
                 num_nodes: flags.num_nodes,
                 node_rank: flags.node_rank,
-                leader_addr: flags.leader_addr.unwrap_or_default(),
+                leader_addr: flags.leader_addr.clone().unwrap_or_default(),
             };
             if node_conf.num_nodes > 1 {
                 if let Ok(Some(if_name)) = net::get_primary_interface().await {
@@ -302,6 +324,19 @@ pub async fn run(
                 }
             }
             if node_conf.node_rank == 0 {
+                let kv_metrics_publisher = if let Some(dyn_input) = &dyn_input {
+                    let kvp_component = dyn_input
+                        .distributed_runtime
+                        .namespace(dyn_input.endpoint_id.namespace.clone())?
+                        .component(KV_PUBLISHER_COMPONENT)?;
+                    let kvp = Arc::new(KvMetricsPublisher::new()?);
+                    let kvp_inner = kvp.clone();
+                    tokio::spawn(async move { kvp_inner.create_endpoint(kvp_component).await });
+                    Some(kvp)
+                } else {
+                    None
+                };
+
                 // vllm multi-node only the leader runs vllm
                 let (engine, vllm_future) = dynamo_engine_vllm::make_leader_engine(
                     cancel_token.clone(),
@@ -309,7 +344,8 @@ pub async fn run(
                     &sock_prefix,
                     node_conf,
                     flags.tensor_parallel_size,
-                    flags.extra_engine_args,
+                    flags.extra_engine_args.clone(),
+                    kv_metrics_publisher,
                 )
                 .await?;
                 extra = Some(Box::pin(async move {
@@ -330,7 +366,6 @@ pub async fn run(
         }
         #[cfg(feature = "llamacpp")]
         Output::LlamaCpp => {
-            use dynamo_engine_llamacpp;
             let Some(model_path) = model_path else {
                 anyhow::bail!("out=llamacpp requires flag --model-path=<full-path-to-model-gguf>");
             };
@@ -408,35 +443,25 @@ pub async fn run(
 
     match in_opt {
         Input::Http => {
-            crate::input::http::run(runtime.clone(), flags.http_port, engine_config).await?;
+            crate::input::http::run(runtime.clone(), flags, engine_config).await?;
         }
         Input::Text => {
-            crate::input::text::run(runtime.clone(), cancel_token.clone(), None, engine_config)
-                .await?;
+            crate::input::text::run(runtime.clone(), flags, None, engine_config).await?;
         }
         Input::Stdin => {
             let mut prompt = String::new();
             std::io::stdin().read_to_string(&mut prompt).unwrap();
-            crate::input::text::run(
-                runtime.clone(),
-                cancel_token.clone(),
-                Some(prompt),
-                engine_config,
-            )
-            .await?;
+            crate::input::text::run(runtime.clone(), flags, Some(prompt), engine_config).await?;
         }
         Input::Batch(path) => {
-            crate::input::batch::run(
-                runtime.clone(),
-                cancel_token.clone(),
-                maybe_card,
-                path,
-                engine_config,
-            )
+            crate::input::batch::run(runtime.clone(), flags, maybe_card, path, engine_config)
                 .await?;
         }
         Input::Endpoint(path) => {
-            crate::input::endpoint::run(runtime.clone(), path, engine_config).await?;
+            let Some(dyn_input) = dyn_input else {
+                unreachable!("We set dyn_input earlier");
+            };
+            crate::input::endpoint::run(dyn_input.distributed_runtime, path, engine_config).await?;
         }
         Input::None => {
             // Multi-node setup. The engine sub-process has been started and is talking

launch/dynamo-run/src/main.rs

@@ -32,7 +32,7 @@ Example:
 
 const ZMQ_SOCKET_PREFIX: &str = "dyn";
 
-const USAGE: &str = "USAGE: dynamo-run in=[http|text|dyn://<path>|batch:<folder>|none] out=[See available engines below] [--http-port 8080] [--model-path <path>] [--model-name <served-model-name>] [--model-config <hf-repo>] [--tensor-parallel-size=1] [--num-nodes=1] [--node-rank=0] [--leader-addr=127.0.0.1:9876] [--base-gpu-id=0] [--extra-engine-args=args.json]";
+const USAGE: &str = "USAGE: dynamo-run in=[http|text|dyn://<path>|batch:<folder>|none] out=[See available engines below] [--http-port 8080] [--model-path <path>] [--model-name <served-model-name>] [--model-config <hf-repo>] [--tensor-parallel-size=1] [--num-nodes=1] [--node-rank=0] [--leader-addr=127.0.0.1:9876] [--base-gpu-id=0] [--extra-engine-args=args.json] [--router-mode random|round-robin]";
 
 fn main() -> anyhow::Result<()> {
     logging::init();
@@ -94,6 +94,7 @@ fn main() -> anyhow::Result<()> {
                         node_config,
                         flags.tensor_parallel_size,
                         flags.extra_engine_args,
+                        flags.router_mode.is_kv_routing(),
                     );
                 }
             } else {

launch/dynamo-run/src/output.rs

-// SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
-// SPDX-License-Identifier: Apache-2.0
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-pub mod common;
-pub mod echo_core;
-pub mod echo_full;

lib/engines/vllm/src/engine.rs

@@ -14,11 +14,13 @@
 // limitations under the License.
 
 use std::path::{Path, PathBuf};
+use std::sync::Arc;
 
 use async_stream::stream;
 use async_trait::async_trait;
 
 use dynamo_llm::engines::MultiNodeConfig;
+use dynamo_llm::kv_router::publisher::KvMetricsPublisher;
 use dynamo_llm::protocols::common::llm_backend::{BackendInput, LLMEngineOutput};
 use dynamo_runtime::engine::{AsyncEngine, AsyncEngineContextProvider, ResponseStream};
 use dynamo_runtime::pipeline::{Error, ManyOut, SingleIn};
@@ -40,6 +42,7 @@ impl VllmEngine {
         node_conf: MultiNodeConfig,
         tensor_parallel_size: u32,
         extra_engine_args: Option<PathBuf>,
+        kv_metrics_publisher: Option<Arc<KvMetricsPublisher>>,
     ) -> anyhow::Result<Self> {
         let w = worker::start(
             cancel_token.clone(),
@@ -48,6 +51,7 @@ impl VllmEngine {
             node_conf,
             tensor_parallel_size,
             extra_engine_args,
+            kv_metrics_publisher,
         )
         .await?;
         let engine = VllmEngine {

lib/engines/vllm/src/lib.rs

@@ -26,6 +26,7 @@ use dynamo_runtime::CancellationToken;
 
 use dynamo_llm::backend::ExecutionContext;
 use dynamo_llm::engines::MultiNodeConfig;
+use dynamo_llm::kv_router::publisher::KvMetricsPublisher;
 
 mod engine;
 use engine::VllmEngine;
@@ -50,6 +51,8 @@ pub async fn make_leader_engine(
     tensor_parallel_size: u32,
     // Path to extra engine args file
     extra_engine_args: Option<PathBuf>,
+    // When using our vllm fork, this is how we publish it's KV metrics for the KV router
+    kv_metrics_publisher: Option<Arc<KvMetricsPublisher>>,
 ) -> pipeline_error::Result<(ExecutionContext, impl Future<Output = ()>)> {
     let ray_obj = if node_conf.num_nodes > 1 {
         let r = ray::start_leader(node_conf.leader_addr.parse()?)?;
@@ -69,6 +72,7 @@ pub async fn make_leader_engine(
         node_conf,
         tensor_parallel_size,
         extra_engine_args,
+        kv_metrics_publisher,
     )
     .await?;
     let vllm_process = engine.take_vllm_worker_handle();

lib/engines/vllm/src/subprocess.rs

@@ -31,7 +31,11 @@ pub fn run_subprocess(
     node_config: MultiNodeConfig,
     tp_size: u32,
     extra_engine_args: Option<PathBuf>,
+    with_kv_routing: bool,
 ) -> anyhow::Result<()> {
+    if with_kv_routing {
+        set_kv_routing_vars()?;
+    }
     pyo3::prepare_freethreaded_python(); // or enable feature "auto-initialize"
     if let Ok(venv) = env::var("VIRTUAL_ENV") {
         let _ = Python::with_gil(|py| crate::fix_venv(venv, py));
@@ -47,6 +51,7 @@ pub fn run_subprocess(
             ("tp_size_str", &tp_size.to_string()),
             ("nnodes_str", &node_config.num_nodes.to_string()),
             ("extra_engine_args", extra_engine_args_str),
+            ("enable_prefix_caching", &with_kv_routing.to_string()),
         ]
         .into_py_dict(py)
         .unwrap();
@@ -57,3 +62,28 @@ pub fn run_subprocess(
         Ok(())
     })
 }
+
+// These environment variables trigger our vllm patch to emit KV routing events
+fn set_kv_routing_vars() -> anyhow::Result<()> {
+    let exe = env::current_exe()?;
+    let exe_dir = exe
+        .parent()
+        .ok_or(anyhow::anyhow!("Current binary has no directory"))?;
+    let mut lib = PathBuf::from(exe_dir);
+    lib.set_file_name("libdynamo_llm_capi.so");
+    let vars = [
+        // Path to the C API Library
+        ("VLLM_KV_CAPI_PATH", lib.display().to_string()),
+        // Identifiers to publish KV related information
+        ("VLLM_KV_NAMESPACE", "dynamo".to_string()),
+        ("VLLM_KV_COMPONENT", "vllm".to_string()),
+        // Worker ID used for identifying workers in distributed settings
+        ("VLLM_WORKER_ID", "0".to_string()),
+    ];
+    for (kvar, default_v) in vars {
+        if env::var(kvar).is_err() {
+            env::set_var(kvar, default_v);
+        }
+    }
+    Ok(())
+}

lib/engines/vllm/src/vllm_inc.py

@@ -36,6 +36,7 @@ arg_map = {
     "max_seq_len_to_capture": 8192,
     "tensor_parallel_size": int(tp_size_str),
     "pipeline_parallel_size": int(nnodes_str),
+    "enable_prefix_caching": enable_prefix_caching.lower() == "true",
 }
 json_map = {}
 if extra_engine_args != "":

lib/engines/vllm/src/worker.rs

@@ -33,11 +33,11 @@ use tokio::io::AsyncBufReadExt;
 use tokio::sync::mpsc::{error::SendError, Sender};
 use tokio::task::JoinHandle;
 
-use dynamo_llm::engines::MultiNodeConfig;
 use dynamo_llm::kv_router::protocols::ForwardPassMetrics;
 use dynamo_llm::protocols::common::llm_backend::LLMEngineOutput;
 use dynamo_llm::protocols::common::preprocessor::PreprocessedRequest;
 use dynamo_llm::protocols::common::FinishReason;
+use dynamo_llm::{engines::MultiNodeConfig, kv_router::publisher::KvMetricsPublisher};
 
 /// Wait this long for the vllm sub-process to stop after we send it a KILL
 const VLLM_STOP_TIMEOUT: Duration = Duration::from_millis(1500);
@@ -164,6 +164,8 @@ pub async fn start(
     _node_conf: MultiNodeConfig,
     tensor_parallel_size: u32,
     extra_engine_args: Option<PathBuf>,
+    // When using our vllm fork, this is how we publish it's KV metrics for the KV router
+    kv_metrics_publisher: Option<Arc<KvMetricsPublisher>>,
 ) -> anyhow::Result<VllmWorker> {
     pyo3::prepare_freethreaded_python(); // or enable feature "auto-initialize"
     if let Ok(venv) = env::var("VIRTUAL_ENV") {
@@ -186,12 +188,17 @@ pub async fn start(
         data,
         tensor_parallel_size,
         extra_engine_args,
+        kv_metrics_publisher.is_some(),
     )
     .await?;
     let vllm_join_handle = watch_vllm(cancel_token.clone(), vllm_process);
 
     tokio::spawn(heartbeat_loop(cancel_token.clone(), heartbeat));
-    tokio::spawn(metrics_loop(cancel_token.clone(), metrics));
+    tokio::spawn(metrics_loop(
+        cancel_token.clone(),
+        metrics,
+        kv_metrics_publisher.clone(),
+    ));
 
     let active_requests = Arc::new(tokio::sync::Mutex::new(HashMap::new()));
     let (tx, rx) = tokio::sync::mpsc::channel(8);
@@ -313,6 +320,7 @@ async fn start_vllm(
     mut data_socket: async_zmq::Dealer<IntoIter<Vec<u8>>, Vec<u8>>,
     tensor_parallel_size: u32,
     extra_engine_args: Option<PathBuf>,
+    with_kv_routing: bool,
 ) -> anyhow::Result<tokio::process::Child> {
     let mut vllm_args = vec![
         "--internal-vllm-process".to_string(),
@@ -322,6 +330,9 @@ async fn start_vllm(
     if let Some(args_path) = extra_engine_args {
         vllm_args.push(format!("--extra-engine-args={}", args_path.display()));
     }
+    if with_kv_routing {
+        vllm_args.push("--router-mode=kv".to_string());
+    }
 
     let self_path = std::env::current_exe()?;
     let mut proc = tokio::process::Command::new(self_path)
@@ -475,7 +486,11 @@ async fn heartbeat_loop(cancel_token: CancellationToken, mut socket: async_zmq::
 }
 
 // NOTE: Custom to our patch of vllm.
-async fn metrics_loop(cancel_token: CancellationToken, mut socket: async_zmq::Pull) {
+async fn metrics_loop(
+    cancel_token: CancellationToken,
+    mut socket: async_zmq::Pull,
+    publisher: Option<Arc<KvMetricsPublisher>>,
+) {
     loop {
         let maybe_metrics = tokio::select! {
             _ = cancel_token.cancelled() => {
@@ -551,15 +566,14 @@ async fn metrics_loop(cancel_token: CancellationToken, mut socket: async_zmq::Pu
 
         match metrics_result {
             Ok(metrics) => {
-                // TODO: These metrics could be attached to StatsHandler or Events
-                // for aggregation and visualization.
-                tracing::debug!("Received vllm metrics: {:?}", metrics);
+                if let Some(metrics_publisher) = publisher.as_ref() {
+                    if let Err(err) = metrics_publisher.publish(metrics.into()) {
+                        tracing::error!(%err, "Failed publishing KV metrics");
+                    }
+                }
             }
             Err(err) => {
-                tracing::error!(
-                    "Error deserializing vllm metrics with Python pickle: {}",
-                    err
-                );
+                tracing::error!("Error deserializing vllm metrics with Python pickle: {err}");
             }
         }
     }

lib/llm/src/http/service/discovery.rs

@@ -22,7 +22,7 @@ use dynamo_runtime::{
     protocols::{self, annotated::Annotated},
     raise,
     transports::etcd::{KeyValue, WatchEvent},
-    DistributedRuntime, Result,
+    DistributedRuntime,
 };
 
 use super::ModelManager;
@@ -60,14 +60,41 @@ pub async fn model_watcher(state: Arc<ModelWatchState>, mut events_rx: Receiver<
 
     while let Some(event) = events_rx.recv().await {
         match event {
-            WatchEvent::Put(kv) => match handle_put(&kv, state.clone()).await {
+            WatchEvent::Put(kv) => {
+                let key = match kv.key_str() {
+                    Ok(key) => key,
+                    Err(err) => {
+                        tracing::error!(%err, ?kv, "Invalid UTF8 in model key");
+                        continue;
+                    }
+                };
+                tracing::debug!(key, "adding model");
+
+                // model_entry.name is the service name (e.g. "Llama-3.2-3B-Instruct")
+                let model_entry = match serde_json::from_slice::<ModelEntry>(kv.value()) {
+                    Ok(model_entry) => model_entry,
+                    Err(err) => {
+                        tracing::error!(%err, ?kv, "Invalid JSON in model entry");
+                        continue;
+                    }
+                };
+                if state.manager.has_model_any(&model_entry.name) {
+                    tracing::trace!(
+                        service_name = model_entry.name,
+                        "New endpoint for existing model"
+                    );
+                    continue;
+                }
+
+                match handle_put(model_entry, state.clone()).await {
                     Ok((model_name, model_type)) => {
                         tracing::info!("added {} model: {}", model_type, model_name);
                     }
                     Err(e) => {
                         tracing::error!("error adding model: {}", e);
                     }
-            },
+                }
+            }
             WatchEvent::Delete(kv) => match handle_delete(&kv, state.clone()).await {
                 Ok((model_name, model_type)) => {
                     tracing::info!("removed {} model: {}", model_type, model_name);
@@ -80,7 +107,10 @@ pub async fn model_watcher(state: Arc<ModelWatchState>, mut events_rx: Receiver<
     }
 }
 
-async fn handle_delete(kv: &KeyValue, state: Arc<ModelWatchState>) -> Result<(&str, ModelType)> {
+async fn handle_delete(
+    kv: &KeyValue,
+    state: Arc<ModelWatchState>,
+) -> anyhow::Result<(&str, ModelType)> {
     let key = kv.key_str()?;
     tracing::debug!(key, "removing model");
 
@@ -98,14 +128,10 @@ async fn handle_delete(kv: &KeyValue, state: Arc<ModelWatchState>) -> Result<(&s
 // models.
 //
 // If this method errors, for the near term, we will delete the offending key.
-async fn handle_put(kv: &KeyValue, state: Arc<ModelWatchState>) -> Result<(String, ModelType)> {
-    let key = kv.key_str()?;
-    tracing::debug!(key, "adding model");
-
-    // model_entry.name is the service name (e.g. "Llama-3.2-3B-Instruct")
-    let model_entry = serde_json::from_slice::<ModelEntry>(kv.value())?;
-    let service_name = model_entry.name.clone();
-
+async fn handle_put(
+    model_entry: ModelEntry,
+    state: Arc<ModelWatchState>,
+) -> anyhow::Result<(String, ModelType)> {
     if model_entry.model_type != state.model_type {
         raise!(
             "model type mismatch: {} != {}",
@@ -125,7 +151,7 @@ async fn handle_put(kv: &KeyValue, state: Arc<ModelWatchState>) -> Result<(Strin
                 .await?;
             state
                 .manager
-                .add_chat_completions_model(&service_name, Arc::new(client))?;
+                .add_chat_completions_model(&model_entry.name, Arc::new(client))?;
         }
         ModelType::Completion => {
             let client = state
@@ -137,9 +163,9 @@ async fn handle_put(kv: &KeyValue, state: Arc<ModelWatchState>) -> Result<(Strin
                 .await?;
             state
                 .manager
-                .add_completions_model(&service_name, Arc::new(client))?;
+                .add_completions_model(&model_entry.name, Arc::new(client))?;
         }
     }
 
-    Ok((service_name, state.model_type))
+    Ok((model_entry.name, state.model_type))
 }

lib/runtime/src/component.rs

@@ -68,7 +68,7 @@ mod namespace;
 mod registry;
 pub mod service;
 
-pub use client::Client;
+pub use client::{Client, RouterMode};
 
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq)]
 #[serde(rename_all = "snake_case")]

lib/runtime/src/component/client.rs

@@ -48,12 +48,25 @@ enum EndpointEvent {
     Delete(String),
 }
 
+#[derive(Default, Debug, Clone, Copy)]
+pub enum RouterMode {
+    #[default]
+    Random,
+    RoundRobin,
+    //KV,
+    //
+    // Always and only go to the given endpoint ID.
+    // TODO: Is this useful?
+    Direct(i64),
+}
+
 #[derive(Clone)]
 pub struct Client<T: Data, U: Data> {
     endpoint: Endpoint,
     router: PushRouter<T, U>,
     counter: Arc<AtomicU64>,
     endpoints: EndpointSource,
+    router_mode: RouterMode,
 }
 
 #[derive(Clone, Debug)]
@@ -74,6 +87,7 @@ where
             endpoint,
             counter: Arc::new(AtomicU64::new(0)),
             endpoints: EndpointSource::Static,
+            router_mode: Default::default(),
         })
     }
 
@@ -157,6 +171,7 @@ where
             endpoint,
             counter: Arc::new(AtomicU64::new(0)),
             endpoints: EndpointSource::Dynamic(watch_rx),
+            router_mode: Default::default(),
         })
     }
 
@@ -177,6 +192,10 @@ where
         }
     }
 
+    pub fn set_router_mode(&mut self, mode: RouterMode) {
+        self.router_mode = mode
+    }
+
     /// Wait for at least one [`Endpoint`] to be available
     pub async fn wait_for_endpoints(&self) -> Result<()> {
         if let EndpointSource::Dynamic(mut rx) = self.endpoints.clone() {
@@ -213,6 +232,7 @@ where
             let offset = counter % count as u64;
             endpoints[offset as usize]
         };
+        tracing::trace!("round robin router selected {endpoint_id}");
 
         let subject = self.endpoint.subject_to(endpoint_id);
         let request = request.map(|req| AddressedRequest::new(req, subject));
@@ -235,6 +255,7 @@ where
             let offset = counter % count as u64;
             endpoints[offset as usize]
         };
+        tracing::trace!("random router selected {endpoint_id}");
 
         let subject = self.endpoint.subject_to(endpoint_id);
         let request = request.map(|req| AddressedRequest::new(req, subject));
@@ -286,10 +307,13 @@ where
     U: Data + for<'de> Deserialize<'de>,
 {
     async fn generate(&self, request: SingleIn<T>) -> Result<ManyOut<U>, Error> {
-        tracing::debug!("Client::generate: {:?}", self.endpoints);
         match &self.endpoints {
             EndpointSource::Static => self.r#static(request).await,
-            EndpointSource::Dynamic(_) => self.random(request).await,
+            EndpointSource::Dynamic(_) => match self.router_mode {
+                RouterMode::Random => self.random(request).await,
+                RouterMode::RoundRobin => self.round_robin(request).await,
+                RouterMode::Direct(endpoint_id) => self.direct(request, endpoint_id).await,
+            },
         }
     }
 }

lib/runtime/src/distributed.rs

@@ -88,6 +88,10 @@ impl DistributedRuntime {
         &self.runtime
     }
 
+    pub fn primary_token(&self) -> CancellationToken {
+        self.runtime.primary_token()
+    }
+
     /// The etcd lease all our components will be attached to.
     /// Not available for static workers.
     pub fn primary_lease(&self) -> Option<etcd::Lease> {