Health Checks

Overview

Dynamo provides health check and liveness HTTP endpoints for each component which can be used to configure startup, liveness and readiness probes in orchestration frameworks such as Kubernetes.

Environment Variables

Getting Started Quickly

Enable health checks and query endpoints:

$
# Start your Dynamo components (default port 8000, override with --http-port or DYN_HTTP_PORT env var)
$
python -m dynamo.frontend &
$
$
# Enable system status server on port 8081
$
DYN_SYSTEM_PORT=8081 python -m dynamo.vllm --model Qwen/Qwen3-0.6B --enforce-eager &

Check health status:

$
# Frontend health (port 8000)
$
curl -s localhost:8000/health | jq
$
$
# Worker health (port 8081)
$
curl -s localhost:8081/health | jq

Frontend Liveness Check

The frontend liveness endpoint reports a status of live as long as the service is running.

Example Request

curl -s localhost:8080/live -q | jq

Example Response

{
  "message": "Service is live",
  "status": "live"
}

Frontend Health Check

The frontend health endpoint reports a status of healthy as long as the service is running. Once workers have been registered, the health endpoint will also list registered endpoints and instances.

Example Request

curl -v localhost:8080/health -q | jq

Example Response

Before workers are registered:

HTTP/1.1 200 OK
content-type: application/json
content-length: 72
date: Wed, 03 Sep 2025 13:31:44 GMT
{
  "instances": [],
  "message": "No endpoints available",
  "status": "unhealthy"
}

After workers are registered:

HTTP/1.1 200 OK
content-type: application/json
content-length: 609
date: Wed, 03 Sep 2025 13:32:03 GMT
{
  "endpoints": [
    "dyn://dynamo.backend.generate"
  ],
  "instances": [
    {
      "component": "backend",
      "endpoint": "clear_kv_blocks",
      "instance_id": 7587888160958628000,
      "namespace": "dynamo",
      "transport": {
        "nats_tcp": "dynamo_backend.clear_kv_blocks-694d98147d54be25"
      }
    },
    {
      "component": "backend",
      "endpoint": "generate",
      "instance_id": 7587888160958628000,
      "namespace": "dynamo",
      "transport": {
        "nats_tcp": "dynamo_backend.generate-694d98147d54be25"
      }
    },
    {
      "component": "backend",
      "endpoint": "load_metrics",
      "instance_id": 7587888160958628000,
      "namespace": "dynamo",
      "transport": {
        "nats_tcp": "dynamo_backend.load_metrics-694d98147d54be25"
      }
    }
  ],
  "status": "healthy"
}

Worker Liveness and Health Check

Health checks for components other than the frontend are enabled selectively based on environment variables. If a health check for a component is enabled the starting status can be set along with the set of endpoints that are required to be served before the component is declared ready.

Once all endpoints declared in DYN_SYSTEM_USE_ENDPOINT_HEALTH_STATUS are served the component transitions to a ready state until the component is shutdown. The endpoints return HTTP status code of HTTP/1.1 503 Service Unavailable when initializing and HTTP status code HTTP/1.1 200 OK once ready.

Example Environment Setting

export DYN_SYSTEM_PORT=9090
export DYN_SYSTEM_STARTING_HEALTH_STATUS="notready"
export DYN_SYSTEM_USE_ENDPOINT_HEALTH_STATUS="[\"generate\"]"

Example Request

curl -v localhost:9090/health | jq

Example Response

Before endpoints are being served:

HTTP/1.1 503 Service Unavailable
content-type: text/plain; charset=utf-8
content-length: 96
date: Wed, 03 Sep 2025 13:42:39 GMT
{
  "endpoints": {
    "generate": "notready"
  },
  "status": "notready",
  "uptime": {
    "nanos": 313803539,
    "secs": 12
  }
}

After endpoints are being served:

HTTP/1.1 200 OK
content-type: text/plain; charset=utf-8
content-length: 139
date: Wed, 03 Sep 2025 13:42:45 GMT
{
  "endpoints": {
    "clear_kv_blocks": "ready",
    "generate": "ready",
    "load_metrics": "ready"
  },
  "status": "ready",
  "uptime": {
    "nanos": 356504530,
    "secs": 18
  }
}

Canary Health Checks (Active Monitoring)

In addition to the HTTP endpoints described above, Dynamo includes a canary health check system that actively monitors worker endpoints.

Overview

The canary health check system:

• Monitors endpoint health by sending periodic test requests to worker endpoints
• Only activates during idle periods - if there’s ongoing traffic, health checks are skipped to avoid overhead
• Automatically enabled in Kubernetes deployments via the operator
• Disabled by default in local/development environments

How It Works

1. Idle Detection: After no activity on an endpoint for a configurable wait time (default: 10 seconds), a canary health check is triggered
2. Health Check Request: A lightweight test request is sent to the endpoint with a minimal payload (generates 1 token)
3. Activity Resets Timer: If normal requests arrive, the canary timer resets and no health check is sent
4. Timeout Handling: If a health check doesn’t respond within the timeout (default: 3 seconds), the endpoint is marked as unhealthy

Configuration

In Kubernetes (Enabled by Default)

Health checks are automatically enabled by the Dynamo operator. No additional configuration is required.

1
apiVersion: nvidia.com/v1alpha1
2
kind: DynamoGraphDeployment
3
metadata:
4
  name: my-deployment
5
spec:
6
  services:
7
    VllmWorker:
8
      componentType: worker
9
      replicas: 2
10
      # Health checks automatically enabled by operator

In Local/Development Environments (Disabled by Default)

To enable health checks locally:

$
# Enable health checks
$
export DYN_HEALTH_CHECK_ENABLED=true
$
$
# Optional: Customize timing
$
export DYN_CANARY_WAIT_TIME=5  # Wait 5 seconds before sending health check
$
export DYN_HEALTH_CHECK_REQUEST_TIMEOUT=5  # 5 second timeout
$
$
# Start worker
$
python -m dynamo.vllm --model Qwen/Qwen3-0.6B

Configuration Options

Health Check Payloads

Each backend defines its own minimal health check payload:

• vLLM: Single token generation with minimal sampling options
• TensorRT-LLM: Single token with BOS token ID
• SGLang: Single token generation request

These payloads are designed to:

• Complete quickly (< 100ms typically)
• Minimize GPU overhead
• Verify the full inference stack is working

Observing Health Checks

When health checks are enabled, you’ll see logs like:

INFO Health check manager started (canary_wait_time: 10s, request_timeout: 3s)
INFO Spawned health check task for endpoint: generate
INFO Canary timer expired for generate, sending health check
INFO Health check successful for generate

If an endpoint fails:

WARN Health check timeout for generate
ERROR Health check request failed for generate: connection refused

When to Use Canary Health Checks

Enable in production (Kubernetes):

• ✅ Detect unhealthy workers before they affect user traffic
• ✅ Enable faster failure detection and recovery
• ✅ Monitor worker availability continuously

Disable in development:

• ✅ Reduce log noise during debugging
• ✅ Avoid overhead when not needed
• ✅ Simplify local testing

Troubleshooting

Health checks timing out:

• Increase DYN_HEALTH_CHECK_REQUEST_TIMEOUT
• Check worker logs for errors
• Verify network connectivity

Too many health check logs:

• Increase DYN_CANARY_WAIT_TIME to reduce frequency
• Or disable with DYN_HEALTH_CHECK_ENABLED=false in dev

Health checks not running:

• Verify DYN_HEALTH_CHECK_ENABLED=true is set
• Check that DYN_SYSTEM_USE_ENDPOINT_HEALTH_STATUS includes the endpoint
• Ensure the worker is serving the endpoint

Related Documentation

• Distributed Runtime Architecture
• Dynamo Architecture Overview
• Backend Guide