Surviving the Packet Storm: A Production Guide to K8s Networking

Most Kubernetes tutorials lie to you. They spin up a `minikube` cluster, curl localhost, and call it a day. In the real world—specifically here in the Nordics where we deal with strict GDPR compliance and users expecting instant responsiveness—the default Kubernetes networking stack is a black box waiting to timeout.

I've spent the last week debugging a microservices cluster that was hemorrhaging packets between worker nodes. The culprit wasn't the code. It wasn't the database. It was a mismatch in MTU settings combined with a noisy neighbor on a budget cloud provider stealing CPU cycles from the software interrupt handler.

If you are running K8s in production in 2025 without understanding CNI implementation details or the impact of underlying hardware, you aren't an engineer; you're a gambler. Let's fix that.

The CNI Battlefield: iptables vs. eBPF

For years, kube-proxy using iptables was the standard. It works, until it doesn't. When you scale to 5,000 services, iptables becomes a sequential list traversal nightmare. Latency spikes. CPU usage creeps up just to route packets.

By late 2024, the industry standard shifted heavily toward eBPF (Extended Berkeley Packet Filter). If you are deploying on CoolVDS today, you should be looking at Cilium. It bypasses the iptables spaghetti entirely.

Here is why this matters for your VPS Norway deployment: eBPF allows for direct routing. No NAT overhead if configured correctly.

Deploying Cilium with Strict Mode

Don't just install the defaults. Enable strict kube-apiserver enforcement to satisfy the security auditors over at Datatilsynet.

helm install cilium cilium/cilium --version 1.16.0 \n  --namespace kube-system \n  --set kubeProxyReplacement=true \n  --set bpf.masquerade=true \n  --set k8sServiceHost=API_SERVER_IP \n  --set k8sServicePort=6443

Pro Tip: If you are migrating a legacy cluster, check your kernel version. CoolVDS KVM instances ship with the latest stable Linux kernels needed for full eBPF feature support. Many budget hosts stick to older kernels to support legacy hypervisors. That breaks eBPF.

The Hidden Latency: VXLAN vs. Direct Routing

Overlay networks (VXLAN/Geneve) are great for portability. They encapsulate your packet inside another packet. But that encapsulation costs CPU. It adds bytes to the header. It creates fragmentation if your MTU isn't tuned.

In a high-performance environment, you want Direct Routing. This means the pod IP is routable on the VPC network. This removes the encapsulation penalty.

However, this requires your underlying infrastructure to support it. This is where the "Cloud" abstraction leaks. If your provider blocks unknown MAC addresses or doesn't allow BGP peering (Bird/FRR), you are stuck with VXLAN.

At CoolVDS, we provide full L2 isolation on our NVMe instances, allowing you to run BGP if you really need to broadcast Pod IPs. But for most, a simple static route setup suffices.

Tuning the MTU

If you must use VXLAN, you must lower the MTU inside the container to account for the header overhead. The standard ethernet MTU is 1500. VXLAN usually requires 50 bytes.

# Check your actual node MTU\nip link show eth0\n\n# If eth0 is 1500, your CNI config must be 1450\n# In Cilium config map:\nmtu: 1450

I've seen entire clusters stall because a 1500-byte packet got dropped silently by a switch that didn't support Jumbo Frames, while the application waited for an ACK that never came.

Ingress is Dead. Long Live Gateway API.

In 2025, if you are still writing massive ingress.yaml files with Nginx-specific annotations, you are creating technical debt. The Kubernetes Gateway API is now the mature standard.

It splits the role of "Cluster Operator" (infrastructure) from "Developer" (routing). It allows for cleaner traffic splitting, header manipulation, and cross-namespace routing without the annotation hell.

Here is a basic HTTPRoute example that splits traffic between a v1 and v2 service—essential for canary deployments which we see often in agile DevOps teams in Oslo.

apiVersion: gateway.networking.k8s.io/v1\nkind: HTTPRoute\nmetadata:\n  name: my-service-route\nspec:\n  parentRefs:\n  - name: external-gateway\n  rules:\n  - matches:\n    - path:\n        type: PathPrefix\n        value: /api\n    backendRefs:\n    - name: my-service-v1\n      port: 8080\n      weight: 90\n    - name: my-service-v2\n      port: 8080\n      weight: 10

The Etcd Bottleneck

You cannot talk about K8s networking without talking about storage. Why? Because Kubernetes stores its network state (Endpoints, Service discovery, IP allocations) in etcd.

If etcd is slow, network updates are slow. If a pod dies and a new one starts, the iptables/eBPF map update is blocked by etcd write latency.

This is where your hosting choice dictates your uptime.

Etcd requires fsync to disk on every write. If you are on a shared VPS with spinning rust or cheap SATA SSDs where the IOPS are throttled, your cluster network will lag.

We use enterprise-grade NVMe drives in RAID configurations specifically to handle the fsync requirements of etcd. Don't let disk I/O kill your network performance.

Local Nuances: Latency to NIX

For our Norwegian clients, physical location matters. The Norwegian Internet Exchange (NIX) in Oslo is the heartbeat of local traffic.

If you host in Frankfurt or London, you are adding 20-30ms of round-trip time (RTT) to every request. For a high-frequency trading bot or a real-time gaming backend, that is eternity. Hosting on CoolVDS ensures your packets stay within the country, routing directly through NIX. This also aids significantly with data residency requirements under GDPR.

Debugging When Things Go Wrong

When the network breaks, don't guess. Use k8s-net-perf to benchmark.

# Run a benchmark between nodes\nkubemc network perf --duration 10s

And never underestimate the power of `conntrack`. A common failure mode in high-traffic clusters is the connection tracking table filling up. The kernel drops packets when this table is full.

Check it on your node:

sysctl net.netfilter.nf_conntrack_count\nsysctl net.netfilter.nf_conntrack_max

If you are hitting the max, bump it up in your `sysctl.conf`. But remember, tracking connections takes RAM. Make sure your VPS has the dedicated memory to support it. CoolVDS guarantees RAM allocation—no ballooning or overcommitment tricks here.

Final Thoughts

Kubernetes networking is complex, but it follows the laws of physics. Reduce the distance (Norwegian datacenters), reduce the overhead (eBPF/NVMe), and monitor the bottlenecks (conntrack/etcd).

Stop fighting with noisy neighbors and fluctuating latency. Deploy a CoolVDS NVMe instance today and give your cluster the foundation it actually needs.