Kubernetes Networking Autopsy: Optimizing CNI, IPVS, and Latency in 2024

If I had a krone for every time a developer told me "the network is slow" and it turned out to be a misconfigured overlay network, I could retire to a cabin in Svalbard. Kubernetes networking is deceptively simple on the surface—Services, Ingress, Pods—but underneath, it is a mess of encapsulation, packet mangling, and latency-inducing hops.

In 2024, running default settings in production is negligence. If you are serving traffic to Oslo or Bergen, relying on standard iptables modes and unoptimized CNIs (Container Network Interfaces) will kill your throughput regardless of how much CPU you throw at the problem.

This isn't a "Hello World" guide. This is a breakdown of how to squeeze every bit of packet performance out of your K8s cluster, ensuring your infrastructure complies with strict Norwegian performance standards and data residency requirements.

The CNI Battlefield: VXLAN vs. BGP vs. eBPF

The default choice for many is Flannel or basic Calico using VXLAN. It works. But VXLAN adds encapsulation overhead. Every packet is wrapped in a UDP packet, sent across the wire, and unwrapped. On a high-traffic node, this CPU tax adds up.

For serious production workloads in June 2024, the industry standard has shifted heavily toward Cilium (eBPF) or Calico (BGP mode).

Why eBPF?

Traditional networking relies on the Linux kernel's network stack (iptables), which was designed decades ago. eBPF allows us to run sandboxed programs in the kernel, bypassing much of that legacy overhead. It is faster. Much faster.

Pro Tip: If you are running on CoolVDS, our underlying KVM architecture supports the latest kernel versions required for advanced eBPF features. Don't try this on legacy hosting providers running ancient CentOS 7 kernels; it won't work.

Here is how you actually deploy Cilium with strict kube-proxy replacement enabled (eliminating iptables entirely for service resolution):

helm install cilium cilium/cilium --version 1.15.5 \
  --namespace kube-system \
  --set kubeProxyReplacement=true \
  --set k8sServiceHost=${API_SERVER_IP} \
  --set k8sServicePort=${API_SERVER_PORT} \
  --set bpf.masquerade=true \
  --set hubble.relay.enabled=true \
  --set hubble.ui.enabled=true

By setting kubeProxyReplacement=true, Cilium handles the load balancing directly in eBPF. I've seen this reduce service latency by 30-40% on high-load clusters compared to standard kube-proxy.

Ditching iptables for IPVS

If you cannot use eBPF for some reason (perhaps legacy kernel requirements or rigid compliance policies), you must at least switch kube-proxy from iptables mode to IPVS (IP Virtual Server).

Iptables is a sequential list of rules. If you have 5,000 services, the kernel has to traverse a massive list of rules to find the match for a single packet. It is O(n). IPVS is hash table-based. It is O(1). Whether you have 10 services or 10,000, the lookup time is virtually identical.

To enable this, you need to modify your kube-proxy config map. But first, ensure the modules are loaded on your underlying VPS nodes:

# Load required modules
modprobe ip_vs
modprobe ip_vs_rr
modprobe ip_vs_wrr
modprobe ip_vs_sh
modprobe nf_conntrack

# Verify they are loaded
lsmod | grep ip_vs

Then, edit the kube-proxy configuration:

apiVersion: kubeproxy.config.k8s.io/v1alpha1
kind: KubeProxyConfiguration
mode: "ipvs"
ipvs:
  strictARP: true
  scheduler: "rr" # Round Robin is usually fine, 'lc' (Least Connection) is better for long-lived connections

The strictARP: true setting is critical if you are using MetalLB for load balancing, which is a common setup on CoolVDS bare-metal-like instances where you handle your own VIPs.

The Hardware Reality: Why Your VPS Provider Matters

You can tune software all day, but you cannot tune away bad physics. Network I/O in a virtualized environment is subject to the "noisy neighbor" effect. If another tenant on the host is blasting UDP traffic, your packet queues fill up. Latency jitters.

When hosting in Norway, specifically for a local user base, the physical distance to the exchange matters. Traffic routed through Frankfurt to reach a user in Trondheim is inefficient.

We use KVM virtualization at CoolVDS. This allows the guest OS (your Kubernetes node) to talk directly to the hypervisor's network stack via VirtIO drivers, minimizing context switches. Combined with NVMe storage (essential for etcd performance, which stores your cluster state), this eliminates the hardware bottleneck.

Gateway API: The New Standard

The Ingress resource was vague. Annotations were a nightmare of vendor-specific hacks. As of mid-2024, the Gateway API (v1.1) is robust enough for production. It separates the role of the Infrastructure Provider (who sets up the LoadBalancer) from the Application Developer (who defines the routes).

Here is an example of a modern HTTPRoute using Gateway API, which offers far more control over traffic splitting (canary deployments) than standard Ingress:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: checkout-route
  namespace: production
spec:
  parentRefs:
  - name: external-gateway
  hostnames:
  - "shop.coolvds.com"
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /checkout
    backendRefs:
    - name: checkout-v2
      port: 8080
      weight: 90
    - name: checkout-v3-beta
      port: 8080
      weight: 10
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add:
          - name: X-Region
            value: "NO-West"

This level of granularity is native. No Nginx annotations required.

MTU: The Silent Killer

A specific war story: We had a client migrating a Magento stack to Kubernetes. Random timeouts on large POST requests. Everything else worked fine.

The culprit? MTU (Maximum Transmission Unit).

The physical network usually has an MTU of 1500. VXLAN adds 50 bytes of header. If your Pod interface is set to 1500, the encapsulated packet becomes 1550 bytes. It gets dropped or fragmented by the physical switch. Fragmentation is slow; drops are fatal.

Always ensure your CNI MTU is lower than the host interface MTU.

# Check host MTU
ip link show eth0 | grep mtu

# Inside the pod (if using VXLAN, should often be 1450 or less)
kubectl exec -it my-pod -- ip link show eth0

On CoolVDS, our network supports Jumbo Frames (MTU 9000) in private networks, which allows you to run VXLAN with a standard 1500 internal MTU without fragmentation. This massive throughput boost is often overlooked.

Data Sovereignty and Routing

Under GDPR and the specific interpretations by the Norwegian Datatilsynet, knowing exactly where your data packets flow is crucial. If your cluster is in Oslo, but your CNI routes traffic through a load balancer in Stockholm or, worse, a US-owned cloud ingress, you have a compliance headache.

Running your own Kubernetes on CoolVDS VPS Norway instances gives you control. You define the BGP peering. You define the ingress points. The data stays in the jurisdiction you expect.

Conclusion

Kubernetes networking is not "set and forget." It requires deliberate choices regarding CNI, proxy modes, and hardware.

1. Use eBPF (Cilium) if your kernel supports it.
2. Use IPVS if you are stuck with kube-proxy.
3. Verify your MTU settings to avoid fragmentation.
4. Host on infrastructure that provides low-latency local peering and NVMe storage.

Don't let network I/O wait times act as the bottleneck for your otherwise optimized code. Deploy a high-performance KVM instance on CoolVDS today and see what sub-5ms latency does for your cluster's response time.