dynamo/docs/pages/components/router

title
Router

Router

The Dynamo KV Router intelligently routes requests by evaluating their computational costs across different workers. It considers both decoding costs (from active blocks) and prefill costs (from newly computed blocks), using KV cache overlap to minimize redundant computation. Optimizing the KV Router is critical for achieving maximum throughput and minimum latency in distributed inference setups.

Quick Start

Python / CLI Deployment

To launch the Dynamo frontend with the KV Router:

python -m dynamo.frontend --router-mode kv --http-port 8000

This command:

• Launches the Dynamo frontend service with KV routing enabled
• Exposes the service on port 8000 (configurable)
• Automatically handles all backend workers registered to the Dynamo endpoint

Backend workers register themselves using the register_model API, after which the KV Router automatically tracks worker state and makes routing decisions based on KV cache overlap.

CLI Arguments

Argument	Default	Description
--router-mode kv	round_robin	Enable KV cache-aware routing
--router-temperature <float>	0.0	Controls routing randomness (0.0 = deterministic, higher = more random)
--kv-cache-block-size <size>	Backend-specific	KV cache block size (should match backend config)
--router-kv-events / --no-router-kv-events	--router-kv-events	Enable/disable real-time KV event tracking
--router-kv-overlap-score-weight <float>	1.0	Balance prefill vs decode optimization (higher = better TTFT).

For all available options: python -m dynamo.frontend --help

Kubernetes Deployment

To enable the KV Router in Kubernetes, add the DYN_ROUTER_MODE environment variable to your frontend service:

apiVersion: nvidia.com/v1alpha1
kind: DynamoGraphDeployment
metadata:
  name: my-deployment
spec:
  services:
    Frontend:
      dynamoNamespace: my-namespace
      componentType: frontend
      replicas: 1
      envs:
        - name: DYN_ROUTER_MODE
          value: kv  # Enable KV Smart Router

Key Points:

• Set DYN_ROUTER_MODE=kv on the Frontend service only
• Workers automatically report KV cache events to the router
• No worker-side configuration changes needed

Environment Variables

All CLI arguments can be configured via environment variables using the DYN_ prefix:

CLI Argument	Environment Variable	Default
--router-mode kv	DYN_ROUTER_MODE=kv	round_robin
--router-temperature	DYN_ROUTER_TEMPERATURE	0.0
--kv-cache-block-size	DYN_KV_CACHE_BLOCK_SIZE	Backend-specific
--no-router-kv-events	DYN_ROUTER_USE_KV_EVENTS=false	true
--router-kv-overlap-score-weight	DYN_ROUTER_KV_OVERLAP_SCORE_WEIGHT	1.0

For complete K8s examples and advanced configuration, see K8s Examples.

For A/B testing and advanced K8s setup, see the KV Router A/B Benchmarking Guide.

For more configuration options and tuning guidelines, see the Router Guide.

Prerequisites and Limitations

Requirements:

• Dynamic endpoints only: KV router requires register_model() with model_input=ModelInput.Tokens. Your backend handler receives pre-tokenized requests with token_ids instead of raw text.
• Backend workers must call register_model() with model_input=ModelInput.Tokens (see Backend Guide)
• You cannot use --static-endpoint mode with KV routing (use dynamic discovery instead)

Multimodal Support:

• TRT-LLM and vLLM: Multimodal routing supported for images via multimodal hashes
• SGLang: Image routing not yet supported
• Other modalities (audio, video, etc.): Not yet supported

Limitations:

• Static endpoints not supported—KV router requires dynamic model discovery via etcd to track worker instances and their KV cache states

For basic model registration without KV routing, use --router-mode round-robin or --router-mode random with both static and dynamic endpoints.

Next Steps

• Router Guide: Deep dive into KV cache routing, configuration, disaggregated serving, and tuning
• Router Examples: Python API usage, K8s examples, and custom routing patterns
• Router Design: Architecture details, algorithms, and event transport modes