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title Service Discovery

Service Discovery

SMG can automatically discover workers in Kubernetes by watching pods with label selectors. Workers are registered and removed as pods scale up or down — no manual URL management needed.

Before you begin

  • Completed the Getting Started guide
  • A Kubernetes cluster with worker pods deployed
  • kubectl configured for your cluster

Basic Setup

Enable service discovery with a label selector that matches your worker pods:

smg \
  --service-discovery \
  --selector app=sglang-worker \
  --service-discovery-namespace inference \
  --service-discovery-port 8000

SMG watches for pods matching the selector and automatically adds or removes workers.

Parameters

Parameter Default Description
--service-discovery false Enable Kubernetes service discovery
--selector — Label selector for worker pods (required)
--service-discovery-namespace default Kubernetes namespace to watch
--service-discovery-port 8000 Port to use for worker connections
--service-discovery-protocol http Protocol: http or grpc

Label Selectors

Single Label

smg --service-discovery --selector app=vllm

Multiple Labels

smg --service-discovery --selector "app=sglang,environment=production"

Matches pods with both labels.

Set-Based Selectors

smg --service-discovery --selector "app in (sglang, vllm),tier=inference"

PD Disaggregation Discovery

For prefill-decode deployments, use separate selectors:

smg \
  --service-discovery \
  --pd-disaggregation \
  --prefill-selector "app=sglang,role=prefill" \
  --decode-selector "app=sglang,role=decode" \
  --service-discovery-namespace inference

Label your pods accordingly:

# Prefill worker pod
metadata:
  labels:
    app: sglang
    role: prefill

# Decode worker pod
metadata:
  labels:
    app: sglang
    role: decode

RBAC

SMG needs permissions to watch pods. Apply these resources to your cluster:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: smg
  namespace: inference
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: smg-discovery
  namespace: inference
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["get", "list", "watch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: smg-discovery
  namespace: inference
subjects:
  - kind: ServiceAccount
    name: smg
    namespace: inference
roleRef:
  kind: Role
  name: smg-discovery
  apiGroup: rbac.authorization.k8s.io

For cross-namespace discovery, use a ClusterRole and ClusterRoleBinding instead.

Deployment Example

SMG Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: smg
  namespace: inference
spec:
  replicas: 1
  selector:
    matchLabels:
      app: smg
  template:
    metadata:
      labels:
        app: smg
    spec:
      serviceAccountName: smg
      containers:
        - name: smg
          image: ghcr.io/lightseekorg/smg:latest
          args:
            - --service-discovery
            - --selector=app=sglang-worker
            - --service-discovery-namespace=inference
            - --service-discovery-port=8000
            - --policy=cache_aware
          ports:
            - containerPort: 8000
              name: http

Worker StatefulSet

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: sglang-worker
  namespace: inference
spec:
  serviceName: sglang-worker
  replicas: 3
  selector:
    matchLabels:
      app: sglang-worker
  template:
    metadata:
      labels:
        app: sglang-worker
    spec:
      containers:
        - name: sglang
          image: lmsysorg/sglang:latest
          args:
            - --model-path=meta-llama/Llama-3.1-8B-Instruct
            - --port=8000
          ports:
            - containerPort: 8000

Verify

# Check discovered workers
curl http://localhost:30000/workers | jq

# Check pod labels match selector
kubectl get pods -n inference -l app=sglang-worker

# Verify RBAC permissions
kubectl auth can-i watch pods -n inference --as=system:serviceaccount:inference:smg

Troubleshooting

Symptom Cause Solution
No workers discovered Wrong selector Verify labels match: kubectl get pods -l <selector>
RBAC error Missing permissions Apply Role and RoleBinding above
Workers not ready Health check failing Check worker health endpoint
Stale workers Watch disconnected Check Kubernetes API connectivity

Next Steps