Surviving the Kubernetes Networking Maze: From Overlay Networks to Production-Grade Ingress

It was 3:45 AM on a Tuesday when the pager screamed. Our production cluster in Oslo had effectively partitioned itself. The pods were running, the nodes were reporting Ready, but traffic? Dead silence. The culprit wasn't the application code; it was a misconfigured MTU setting inside our overlay network that fragmented packets silently until the whole mesh collapsed.

If you have been running Kubernetes (we are on version 1.5.3 now) for more than a week, you know the networking layer is where the magic happens—and where the bodies are buried. While everyone else is excited about the shiny new features in the upcoming 1.6 release, we need to talk about the plumbing that keeps your cluster alive right now.

This isn't a high-level overview for managers. This is a deep dive into the messy reality of CNI plugins, iptables hell, and why your underlying VPS Norway infrastructure dictates your network performance more than you think.

The Flat Network Illusion

Kubernetes promises a flat network where every pod can talk to every other pod without NAT. Beautiful on paper. In reality, achieving this requires an intricate dance of routing rules and encapsulation. By default, you are likely using Flannel or Weave. These create an overlay network, encapsulating your packets inside VXLAN or UDP headers.

Here is the problem: Encapsulation costs CPU.

Every packet leaving a pod gets wrapped, sent over the wire, and unwrapped at the destination. On a shared, oversold VPS, this "overlay tax" creates jitter. I've seen database latency spike from 2ms to 200ms just because the noisy neighbor on the physical host stole CPU cycles during the encapsulation process.

The CNI Dilemma: Flannel vs. Calico

In 2017, the choice usually comes down to simplicity vs. performance.

• Flannel (VXLAN): Easy to set up. Great for demos. Terrible if you haven't tuned your MTU to account for the extra header size.
• Calico (BGP): Pure Layer 3 routing. No encapsulation overhead if your network supports it. It turns your nodes into virtual routers.

If you are deploying on CoolVDS, we typically recommend looking at Calico or host-gw backends because our KVM instances provide the raw kernel access necessary to handle BGP peering efficiently, without the "steal time" penalty of lesser providers.

Deep Dive: The iptables Nightmare

When you create a Service in Kubernetes, you aren't creating a load balancer; you are creating a logical concept implemented via iptables rules on every single node. The kube-proxy component watches the API server and updates these rules.

Let's look at what actually happens when you run a standard service definition:

apiVersion: v1
kind: Service
metadata:
  name: backend-service
spec:
  selector:
    app: backend
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376

Behind the scenes, kube-proxy generates a chaotic list of NAT rules. You can see this mess by running:

sudo iptables-save | grep backend-service

You will see output resembling this:

-A KUBE-SEP-... -s 10.244.1.5/32 -m comment --comment "default/backend-service:" -j KUBE-MARK-MASQ
-A KUBE-SERVICES -d 10.100.20.5/32 -p tcp -m comment --comment "default/backend-service: cluster IP" -m tcp --dport 80 -j KUBE-SVC-...

As your cluster grows to thousands of services, iptables becomes a bottleneck. The kernel has to process these rules sequentially. This is O(n) complexity. If you have 5,000 services, every packet has to traverse a massive list of rules. This is why latency creeps up on large clusters.

Pro Tip: If you notice kube-proxy consuming high CPU, check your service count. On CoolVDS, we mitigate this by offering high-frequency CPUs that chew through rule evaluation faster, but architectural limits still apply. Keep an eye on the alpha ipvs work—it might save us in the future, but for 2017, we are stuck with iptables.

Ingress: Stop Using NodePorts

I still see developers exposing apps via type: NodePort and putting an external load balancer in front of it. Stop. It's messy, it burns a port on every node, and it complicates your firewall rules.

The standard in 2017 is the Nginx Ingress Controller. It runs as a pod, listens on port 80/443, and routes traffic based on host headers. It reduces the complexity of your edge network significantly.

Here is a battle-tested Ingress configuration we use for high-traffic endpoints:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: production-ingress
  annotations:
    kubernetes.io/ingress.class: "nginx"
    # Critical for handling large file uploads without timeouts
    ingress.kubernetes.io/proxy-body-size: "50m"
    ingress.kubernetes.io/proxy-read-timeout: "600"
    # Enable sticky sessions if your legacy app needs them
    ingress.kubernetes.io/affinity: "cookie"
spec:
  rules:
  - host: api.coolvds-demo.no
    http:
      paths:
      - path: /
        backend:
          serviceName: backend-service
          servicePort: 80

The Storage-Network Link: Etcd Latency

You cannot talk about Kubernetes networking without talking about etcd. Etcd stores the state of the network. If etcd is slow, kube-proxy updates are slow, and your service discovery lags.

Etcd is incredibly sensitive to disk write latency (fsync). If your VPS provider puts you on standard SATA SSDs (or worse, spinning rust), your cluster will become unstable under load. The network configuration won't update fast enough during a rolling update, causing 502 errors.

This is where hardware choice becomes a "make or break" factor. At CoolVDS, we enforce NVMe storage for all instances. We've seen etcd write latencies drop from 15ms on standard SSDs to sub-1ms on our NVMe arrays. That difference is the stability margin between a successful deploy and a pager duty call.

The Norwegian Context: Latency and Compliance

Hosting in Norway isn't just about patriotism; it's physics and law. With the Datatilsynet ramping up privacy requirements (and the EU's GDPR framework looming for next year), keeping data within national borders is becoming a hard requirement for many CTOs.

Furthermore, latency to the NIX (Norwegian Internet Exchange) in Oslo matters. If your Kubernetes nodes are in Frankfurt but your users are in Bergen, you are adding 20-30ms of round-trip time before the packet even hits your overlay network. Hosting locally on CoolVDS cuts that transport latency to near zero, giving you more budget for the inevitable Java application slowness.

Final Thoughts

Kubernetes networking in 2017 is powerful, but it is not magic. It is a complex stack of encapsulation, routing tables, and kernel rules. It demands respect, and more importantly, it demands robust infrastructure.

Don't let IO wait times or noisy neighbors destabilize your pod network. Build on a foundation that respects the packet.

Need a cluster that doesn't choke on packet fragmentation? Spin up a high-performance KVM instance on CoolVDS today and see the difference raw NVMe power makes.