Add --migration-limit flag

Author: kthui

launch/dynamo-run/src/flags.rs

@@ -161,6 +161,11 @@ pub struct Flags {
     #[arg(long)]
     pub request_template: Option<PathBuf>,
 
+    /// How many times a request can be migrated to another worker if the HTTP server lost
+    /// connection to the current worker.
+    #[arg(long, value_parser = clap::value_parser!(u32).range(0..1024))]
+    pub migration_limit: Option<u32>,
+
     /// Everything after a `--`.
     /// These are the command line arguments to the python engine when using `pystr` or `pytok`.
     #[arg(index = 2, last = true, hide = true, allow_hyphen_values = true)]
@@ -179,6 +184,9 @@ impl Flags {
                 if self.kv_cache_block_size.is_some() {
                     anyhow::bail!("'--kv-cache-block-size' flag should only be used on the worker node, not on the ingress");
                 }
+                if self.migration_limit.is_some() {
+                    anyhow::bail!("'--migration-limit' flag should only be used on the worker node, not on the ingress");
+                }
             }
             Output::EchoFull => {}
             Output::EchoCore => {

launch/dynamo-run/src/lib.rs

@@ -44,7 +44,8 @@ pub async fn run(
         .context_length(flags.context_length)
         .http_port(Some(flags.http_port))
         .router_config(flags.router_config())
-        .request_template(flags.request_template.clone());
+        .request_template(flags.request_template.clone())
+        .migration_limit(flags.migration_limit);
 
     // If `in=dyn` we want the trtllm/sglang/vllm subprocess to listen on that endpoint.
     // If not, then the endpoint isn't exposed so we let LocalModel invent one.

launch/dynamo-run/src/subprocess.rs

@@ -48,6 +48,8 @@ pub async fn start(
         card.kv_cache_block_size.to_string(),
         "--context-length".to_string(),
         card.context_length.to_string(),
+        "--migration-limit".to_string(),
+        card.migration_limit.to_string(),
     ];
     // TRTLLM only
     // The worker node will only publish events and metrics if the router mode is KV

launch/dynamo-run/src/subprocess/sglang_inc.py

@@ -42,6 +42,7 @@ class Config:
     nnodes: int
     node_rank: int
     dist_init_addr: str
+    migration_limit: int
     extra_engine_args: str
 
 
@@ -202,7 +203,13 @@ async def init(runtime: DistributedRuntime, config: Config):
     model_type = (
         ModelType.Backend if not engine_args.is_embedding else ModelType.Embedding
     )
-    await register_llm(model_type, endpoint, config.model_path, config.model_name)
+    await register_llm(
+        model_type,
+        endpoint,
+        config.model_path,
+        config.model_name,
+        migration_limit=config.migration_limit,
+    )
 
     # the server will gracefully shutdown (i.e., keep opened TCP streams finishes)
     # after the lease is revoked
@@ -268,6 +275,12 @@ def cmd_line_args():
         default="",
         help="Host address (e.g., `192.168.0.2:25000`) of the node with rank 0",
     )
+    parser.add_argument(
+        "--migration-limit",
+        type=int,
+        default=0,
+        help="Maximum number of times a request may be migrated to a different engine worker. The number may be overridden by the engine.",
+    )
     parser.add_argument(
         "--extra-engine-args",
         type=str,
@@ -304,6 +317,7 @@ def cmd_line_args():
     config.nnodes = args.nnodes
     config.node_rank = args.node_rank
     config.dist_init_addr = args.dist_init_addr
+    config.migration_limit = args.migration_limit
     config.extra_engine_args = args.extra_engine_args
     return config
 

launch/dynamo-run/src/subprocess/trtllm_inc.py

@@ -122,6 +122,7 @@ class Config:
     model_name: Optional[str] = None
     tensor_parallel_size: int
     kv_block_size: int
+    migration_limit: int
     extra_engine_args: str
     publish_events_and_metrics: bool
     disaggregation_mode: str
@@ -136,6 +137,7 @@ def __str__(self) -> str:
             f"model_name={self.model_name}, "
             f"tensor_parallel_size={self.tensor_parallel_size}, "
             f"kv_block_size={self.kv_block_size}, "
+            f"migration_limit={self.migration_limit}, "
             f"extra_engine_args={self.extra_engine_args}, "
             f"publish_events_and_metrics={self.publish_events_and_metrics}, "
             f"disaggregation_mode={self.disaggregation_mode}, "
@@ -404,6 +406,7 @@ async def init(runtime: DistributedRuntime, config: Config):
                 config.model_path,
                 config.model_name,
                 kv_cache_block_size=config.kv_block_size,
+                migration_limit=config.migration_limit,
             )
 
         # publisher will be set later if publishing is enabled.
@@ -476,6 +479,12 @@ def cmd_line_args():
         default=None,
         help="This argument is not used by TRTLLM. Please provide max_input_len, max_seq_len and max_output_len in yaml file and point --extra-engine-args to the yaml file.",
     )
+    parser.add_argument(
+        "--migration-limit",
+        type=int,
+        default=0,
+        help="Maximum number of times a request may be migrated to a different engine worker. The number may be overridden by the engine.",
+    )
     parser.add_argument(
         "--extra-engine-args",
         type=str,
@@ -557,6 +566,7 @@ def cmd_line_args():
     config.endpoint = parsed_endpoint_name
     config.tensor_parallel_size = args.tensor_parallel_size
     config.kv_block_size = args.kv_block_size
+    config.migration_limit = args.migration_limit
     config.extra_engine_args = args.extra_engine_args
     config.publish_events_and_metrics = args.publish_events_and_metrics
     config.disaggregation_mode = disaggregation_mode

launch/dynamo-run/src/subprocess/vllm_inc.py

@@ -56,6 +56,7 @@ class Config:
     tensor_parallel_size: int
     kv_block_size: int
     context_length: int
+    migration_limit: int
     extra_engine_args: str
 
 
@@ -233,6 +234,7 @@ async def init(runtime: DistributedRuntime, config: Config):
             "max_model_len", None
         ),  # if None, takes length from tokenizer
         kv_cache_block_size=arg_map["block_size"],
+        migration_limit=config.migration_limit,
     )
     handler = RequestHandler(component, engine_client, default_sampling_params)
     handler.setup_kv_metrics()
@@ -276,6 +278,12 @@ def cmd_line_args():
         default=None,
         help="Max model context length. Defaults to models max, usually model_max_length from tokenizer_config.json. Reducing this reduces VRAM requirements.",
     )
+    parser.add_argument(
+        "--migration-limit",
+        type=int,
+        default=0,
+        help="Maximum number of times a request may be migrated to a different engine worker. The number may be overridden by the engine.",
+    )
     parser.add_argument(
         "--extra-engine-args",
         type=str,
@@ -308,6 +316,7 @@ def cmd_line_args():
     config.tensor_parallel_size = args.tensor_parallel_size
     config.kv_block_size = args.kv_block_size
     config.context_length = args.context_length
+    config.migration_limit = args.migration_limit
     config.extra_engine_args = args.extra_engine_args
 
     return config

launch/dynamo-run/src/subprocess/vllm_v1_inc.py

@@ -65,6 +65,7 @@ class Config:
     tensor_parallel_size: int
     kv_block_size: int
     context_length: int
+    migration_limit: int
     extra_engine_args: str
 
 
@@ -218,6 +219,7 @@ async def init(runtime: DistributedRuntime, config: Config):
         config.model_path,
         config.model_name,
         kv_cache_block_size=config.kv_block_size,
+        migration_limit=config.migration_limit,
     )
 
     arg_map = {
@@ -333,6 +335,12 @@ def cmd_line_args():
         default=None,
         help="Max model context length. Defaults to models max, usually model_max_length from tokenizer_config.json. Reducing this reduces VRAM requirements.",
     )
+    parser.add_argument(
+        "--migration-limit",
+        type=int,
+        default=0,
+        help="Maximum number of times a request may be migrated to a different engine worker. The number may be overridden by the engine.",
+    )
     parser.add_argument(
         "--extra-engine-args",
         type=str,
@@ -365,6 +373,7 @@ def cmd_line_args():
     config.tensor_parallel_size = args.tensor_parallel_size
     config.kv_block_size = args.kv_block_size
     config.context_length = args.context_length
+    config.migration_limit = args.migration_limit
     config.extra_engine_args = args.extra_engine_args
 
     return config

lib/bindings/python/rust/lib.rs

@@ -129,7 +129,7 @@ fn log_message(level: &str, message: &str, module: &str, file: &str, line: u32)
 }
 
 #[pyfunction]
-#[pyo3(signature = (model_type, endpoint, model_path, model_name=None, context_length=None, kv_cache_block_size=None, router_mode=None))]
+#[pyo3(signature = (model_type, endpoint, model_path, model_name=None, context_length=None, kv_cache_block_size=None, router_mode=None, migration_limit=0))]
 #[allow(clippy::too_many_arguments)]
 fn register_llm<'p>(
     py: Python<'p>,
@@ -140,6 +140,7 @@ fn register_llm<'p>(
     context_length: Option<u32>,
     kv_cache_block_size: Option<u32>,
     router_mode: Option<RouterMode>,
+    migration_limit: u32,
 ) -> PyResult<Bound<'p, PyAny>> {
     let model_type_obj = match model_type {
         ModelType::Chat => llm_rs::model_type::ModelType::Chat,
@@ -160,7 +161,8 @@ fn register_llm<'p>(
             .model_name(model_name)
             .context_length(context_length)
             .kv_cache_block_size(kv_cache_block_size)
-            .router_config(router_config);
+            .router_config(router_config)
+            .migration_limit(Some(migration_limit));
         // Download from HF, load the ModelDeploymentCard
         let mut local_model = builder.build().await.map_err(to_pyerr)?;
         // Advertise ourself on etcd so ingress can find us

lib/llm/src/local_model.rs

@@ -46,6 +46,7 @@ pub struct LocalModelBuilder {
     router_config: Option<RouterConfig>,
     kv_cache_block_size: u32,
     http_port: u16,
+    migration_limit: u32,
 }
 
 impl Default for LocalModelBuilder {
@@ -60,6 +61,7 @@ impl Default for LocalModelBuilder {
             context_length: Default::default(),
             template_file: Default::default(),
             router_config: Default::default(),
+            migration_limit: Default::default(),
         }
     }
 }
@@ -112,6 +114,11 @@ impl LocalModelBuilder {
         self
     }
 
+    pub fn migration_limit(&mut self, migration_limit: Option<u32>) -> &mut Self {
+        self.migration_limit = migration_limit.unwrap_or(0);
+        self
+    }
+
     /// Make an LLM ready for use:
     /// - Download it from Hugging Face (and NGC in future) if necessary
     /// - Resolve the path
@@ -137,10 +144,12 @@ impl LocalModelBuilder {
 
         // echo_full engine doesn't need a path. It's an edge case, move it out of the way.
         if self.model_path.is_none() {
+            let mut card = ModelDeploymentCard::with_name_only(
+                self.model_name.as_deref().unwrap_or(DEFAULT_NAME),
+            );
+            card.migration_limit = self.migration_limit;
             return Ok(LocalModel {
-                card: ModelDeploymentCard::with_name_only(
-                    self.model_name.as_deref().unwrap_or(DEFAULT_NAME),
-                ),
+                card,
                 full_path: PathBuf::new(),
                 endpoint_id,
                 template,
@@ -194,6 +203,8 @@ impl LocalModelBuilder {
             card.context_length = context_length;
         }
 
+        card.migration_limit = self.migration_limit;
+
         Ok(LocalModel {
             card,
             full_path,