Customizing Cilium on an OVHcloud Managed Kubernetes cluster

Objective

The OVHcloud Managed Kubernetes Service provides you with Kubernetes clusters without the hassle of installing or operating them.

The Standard plan of OVHcloud Managed Kubernetes clusters uses Cilium as the default CNI.

The Cilium agent process (a.k.a. DaemonSet) allows configuration on a per-node basis.

This allows overriding cilium-config ConfigMap for a node or set of nodes by using CiliumNodeConfig objects.

Requirements

• An OVHcloud Managed Kubernetes cluster with Standard plan.

Instructions

What is CiliumNodeConfig

As stated in Cilium documentation:

A CiliumNodeConfig object allows for overriding ConfigMap / Agent arguments.

It consists of a set of fields and a label selector. The label selector defines to which nodes the configuration applies.

As is the standard with Kubernetes, an empty LabelSelector (e.g. {}) selects all nodes.

CiliumNodeConfig possible values

You can find the full list of possible keys and values in the cilium-configmap file on GitHub.

Customization example

Enable topology aware routing for 3AZ region

To enable topology aware routing for 3AZ region on the Cilium side, apply this configuration of CiliumNodeConfig:

apiVersion: cilium.io/v2
kind: CiliumNodeConfig
metadata:
  namespace: kube-system
  name: enable-service-topology
spec:
  nodeSelector: {}
  defaults:
    enable-service-topology: "true"

Then restart the Cilium agent:

kubectl -n kube-system rollout restart daemonset cilium

Verify that the configuration has been applied:

kubectl -n kube-system logs $(kubectl -n kube-system get pod -l k8s-app=cilium -o name) | head -n 500 | grep enable-service-topology

time=2025-12-09T15:57:06.161145191Z level=info msg="  --config-sources='[{\"kind\":\"config-map\",\"namespace\":\"kube-system\",\"name\":\"cilium-config\"},{\"kind\":\"cilium-node-config\",\"namespace\":\"kube-system\",\"name\":\"enable-service-topology\"}]'"
time=2025-12-09T15:57:06.165626171Z level=info msg="  --enable-service-topology='true'"

Go further

To have an overview of the OVHcloud Managed Kubernetes Service, see this page.

To learn more about how to use your Kubernetes cluster the practical way, we invite you to read our tutorials.

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