Kubernetes Networking in 2025: Bypassing the Overlay Tax for Nordic Low-Latency

Most Kubernetes clusters are built on a lie. The lie is that network abstraction comes without a cost. I’ve spent the last six months debugging a microservices mesh for a fintech client in Oslo, and I can tell you: if you ignore the packet path, your latency will eat your SLA alive. While abstractions like Services and Ingress make developers' lives easier, they often introduce hops that add double-digit milliseconds to requests. In the Norwegian market, where traffic hits NIX (Norwegian Internet Exchange) in Oslo almost instantly, adding 15ms inside your cluster is unacceptable.

It is July 2025. If you are still relying on iptables-heavy routing or unoptimized VXLAN encapsulation, you are doing it wrong. Let’s rip open the networking stack and fix it.

The CNI Battlefield: eBPF is No Longer Optional

Years ago, we debated Flannel vs. Weave. Today, that debate is dead. For high-performance workloads, specifically those hosted on Virtual Dedicated Servers (VDS) where you have more control than in managed hyperscaler environments, eBPF-based CNIs are the baseline. Cilium has effectively won this war.

Why? Because iptables is a linked list. When you scale to 5,000 services, the kernel has to traverse that list sequentially. eBPF (Extended Berkeley Packet Filter) allows us to run sandboxed programs in the kernel, turning O(n) lookups into O(1) hash table lookups.

Pro Tip: When deploying on CoolVDS, enable the kube-proxy-replacement strict mode in Cilium. Since our KVM instances provide stable virtio-net drivers, you can bypass netfilter entirely for east-west traffic.

Configuration: Enabling Direct Routing

The biggest mistake I see is enabling VXLAN (encapsulation) when the underlying infrastructure supports Direct Routing. Encapsulation adds CPU overhead for wrapping/unwrapping packets and reduces the MTU (Maximum Transmission Unit), causing fragmentation. If your nodes share a Layer 2 domain—which they do in CoolVDS private VLANs—turn off the tunnel.

Here is the Helm configuration for a 2025-era Cilium install optimized for our infrastructure:

helm install cilium cilium/cilium --version 1.16.2 \
  --namespace kube-system \
  --set tunnel=disabled \
  --set autoDirectNodeRoutes=true \
  --set ipv4.nativeRoutingCIDR=10.0.0.0/16 \
  --set loadBalancer.mode=dsr \
  --set kubeProxyReplacement=true \
  --set bpf.masquerade=true

Notice loadBalancer.mode=dsr (Direct Server Return). This ensures that the response packet goes directly from the backend pod to the client, bypassing the load balancer node on the return trip. For bandwidth-heavy applications like media streaming, this cuts throughput bottlenecks in half.

Ingress vs. Gateway API: The 2025 Standard

The old Ingress resource is in maintenance mode. If you are building new clusters today, use the Gateway API. It decouples the infrastructure provisioning (Gateway) from the routing configuration (HTTPRoute), allowing Ops to define the entry point and Devs to define the paths.

However, complexity is the enemy. A misconfigured Gateway API can lead to "split-brain" routing scenarios. Here is a production-ready HTTPRoute that handles traffic splitting (canary deployment) for a strictly compliant Norwegian service:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: payment-processor
  namespace: finance
spec:
  parentRefs:
  - name: external-gateway
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /api/v2
    backendRefs:
    - name: payment-service-v2
      port: 8080
      weight: 95
    - name: payment-service-canary
      port: 8080
      weight: 5
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
        - name: X-Region
          value: "NO-OSL-1"

This configuration explicitly tags requests with the region. When hosting on CoolVDS, we often see clients use this header to enforce data residency rules, ensuring logs processed by sidecars don't accidentally leak metadata outside of Norway, satisfying strict GDPR interpretations.

Debugging the Black Box: When Packets Vanish

It happens. A service returns 504. The logs are empty. The culprit is almost always a network policy dropping traffic or a conntrack table exhaustion. In 2025, we don't install tcpdump on production images (it's a security risk). We use ephemeral debug containers.

kubectl debug -it -n finance pod/payment-service-v2 --image=nicolaka/netshoot --target=payment-service-v2

Once inside, don't just look at traffic. Look at the drops. Using pwru (Packet Where Are You), an eBPF-based tracer, is far more effective than tcpdump for understanding kernel decisions.

# Check for drops on the specific interface
pwru --output-tuple 'host 10.244.1.5 and port 8080' --filter-func 'kfree_skb'

If you see kfree_skb (kernel free socket buffer) triggering frequently, your node is dropping packets, likely due to buffer exhaustion. This brings us to the infrastructure reality.

Infrastructure Matters: The CoolVDS Advantage

You can tune sysctl until your fingers bleed, but if the hypervisor steals CPU cycles during network interrupts, your latency jitter will ruin the user experience. Many VPS providers oversell CPU, leading to "noisy neighbor" effects that manifest as network latency.

We ran a benchmark comparing a standard shared VPS against a CoolVDS NVMe instance running a Redis cluster behind Envoy proxy. We measured P99 latency during a simulated DDoS attack (SYN flood).

The difference lies in the SR-IOV capabilities and dedicated CPU pinning available on CoolVDS. K8s networking is CPU intensive. Encryption (mTLS), encapsulation, and routing all burn cycles. If your CPU is waiting for the hypervisor, your packets are waiting in a queue.

Final Thoughts: Keep It Local, Keep It Fast

Norwegian users expect instant response times. Whether you are serving media content to Tromsø or financial data in Oslo, the physics of networking applies. Use eBPF to bypass the kernel bloat, use Direct Routing to avoid the encapsulation tax, and run it on metal that respects your need for raw I/O.

Your Kubernetes cluster is a race car. Don't put it on a dirt road. If you need to test a Direct Routing configuration with full root access and zero noisy neighbors, spin up a CoolVDS instance. It takes 55 seconds, and your P99 latency will thank you.