Cilium is an open-source networking, observability, and security solution for cloud-native environments, such as Kubernetes clusters. It leverages eBPF (extended Berkeley Packet Filter) technology to provide high-performance networking and security features. Cilium is particularly known for its ability to enforce network policies, provide load balancing, and offer deep visibility into network traffic.
One common issue users may encounter is Cilium not resolving DNS queries. This symptom manifests as applications within the Kubernetes cluster being unable to resolve domain names, leading to connectivity issues with external services or other pods within the cluster.
The root cause of DNS resolution issues in Cilium often stems from misconfigurations in the DNS proxy settings or restrictive network policies that inadvertently block DNS traffic. Cilium uses a DNS proxy to intercept and manage DNS requests, and any misconfiguration here can lead to failures in DNS resolution.
Misconfigurations can occur if the DNS proxy settings are not correctly aligned with the cluster's DNS server settings. This can prevent DNS requests from being properly intercepted and forwarded.
Network policies in Cilium are used to control the flow of traffic between pods. If these policies are too restrictive, they may block DNS traffic, preventing successful DNS resolution.
First, ensure that the DNS proxy is correctly configured. Check the Cilium configuration file (usually located at /etc/cilium/cilium.yaml) for the DNS proxy settings. Ensure that the enable-dns-proxy option is set to true and that the dns-proxy-port is correctly specified.
kubectl -n kube-system edit configmap cilium-config
Look for the following settings:
enable-dns-proxy: "true"
dns-proxy-port: "53"
After making changes, restart the Cilium pods to apply the new configuration:
kubectl -n kube-system rollout restart daemonset cilium
Next, review the network policies applied in your cluster. Ensure that there are no policies blocking DNS traffic. You can list all network policies using:
kubectl get networkpolicy --all-namespaces
Inspect each policy to ensure DNS traffic is allowed. A typical policy allowing DNS traffic might look like this:
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: allow-dns
spec:
podSelector: {}
policyTypes:
- Egress
egress:
- to:
- ports:
- protocol: UDP
port: 53
After verifying and adjusting configurations, test DNS resolution from within a pod:
kubectl exec -it -- nslookup google.com
If DNS resolution works, the issue is resolved. If not, further investigation into logs and configurations may be necessary.
For more detailed information on configuring Cilium, refer to the Cilium Documentation. For troubleshooting network policies, the Kubernetes Network Policies Guide is a valuable resource.
(Perfect for DevOps & SREs)
(Perfect for DevOps & SREs)
