Smarter Traffic Routing with Kubernetes

Kubernetes networking just got smarter in v1.34. With the new spec.trafficDistribution field in Services, you can now influence traffic locality without a service mesh.

What is trafficDistribution?

The spec.trafficDistribution field gives you a hint-based mechanism to control how Kubernetes routes traffic to endpoints. The initial supported value is PreferClose, which tells kube-proxy and compatible implementations to prefer endpoints topologically closer to the client.

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app
  ports:
  - port: 80
    targetPort: 8080
  trafficDistribution: PreferClose

How PreferClose Works

When PreferClose is set:

1. Same zone first — kube-proxy prioritises endpoints in the same availability zone as the client pod
2. Same region fallback — if no same-zone endpoints are available, traffic goes to the same region
3. Any endpoint last resort — if neither of the above apply, any healthy endpoint is used

This is implemented through EndpointSlice hints that each node's kube-proxy reads when making forwarding decisions.

Why This Matters

Before trafficDistribution, achieving topology-aware routing required either:

• A service mesh (Istio, Linkerd)
• The older topologyKeys field (now deprecated)
• External traffic policy tricks with NodePort services

Now you get basic locality preference with a single field — no sidecar injection, no mesh control plane overhead.

Comparison: trafficDistribution vs Topology Aware Routing

When to Use It

Use trafficDistribution: PreferClose when:

• You have a multi-zone cluster and want to reduce cross-zone data transfer costs
• Latency between zones matters for your application
• You don't need the full complexity of a service mesh

Don't rely on it as a strict guarantee — it's a hint, not a hard rule. For hard traffic shaping (canary deployments, weighted routing, circuit breaking), you still need a service mesh or gateway-level solution.

Enabling It

The field is enabled by default from Kubernetes v1.34. For earlier versions, enable the ServiceTrafficDistribution feature gate:

# On kube-apiserver and kube-proxy
--feature-gates=ServiceTrafficDistribution=true

Checking Endpoint Hints

You can inspect the hints kube-proxy is using by looking at EndpointSlices:

kubectl get endpointslices -l kubernetes.io/service-name=my-service -o yaml

Look for the hints field under each endpoint — it will show the zones that endpoint is hinted for.

Summary

spec.trafficDistribution is a lightweight, mesh-free way to reduce cross-zone latency and egress costs in Kubernetes. For the majority of services that just need locality preference without complex traffic policies, it removes the need to adopt a full service mesh. For advanced use cases — canaries, retries, circuit breaking, mTLS — a service mesh remains the right tool.