KubernetesDNS

KubernetesDNS refers to the internal DNS service used by Kubernetes clusters to provide name resolution for pods and services. It enables components and applications running in the cluster to discover and reach each other by name rather than by IP address, supporting reliable service discovery.

In modern Kubernetes installations, the DNS service is implemented by CoreDNS and runs as a Deployment in the kube-system namespace, often under the name coredns. Earlier setups used kube-dns. CoreDNS watches the Kubernetes API for changes to services, endpoints, and pods, and it serves DNS records that reflect the current cluster state. The DNS service is exposed inside the cluster as a stable DNS name, and pods are configured to use its cluster IP by default.

DNS naming within the cluster uses a hierarchical domain, typically cluster.local. For a standard service named my-service in namespace default, the name my-service.default.svc.cluster.local resolves to the service’s cluster IP. For headless services (where the service has no cluster IP), DNS can return a set of A records for each pod IP behind the service, allowing direct pod access when needed. Queries for endpoints and related records can also be resolved through CoreDNS.

Configuration of the DNS service is controlled by a CoreDNS ConfigMap (usually named coredns) in the kube-system namespace. The Corefile specifies how queries are handled, and the kubernetes plugin enables dynamic resolution from the Kubernetes API. Administrators can customize upstream resolvers, add stub domains, or enable metrics and logging as needed.

Troubleshooting typically involves verifying the CoreDNS pods, inspecting the CoreDNS ConfigMap, checking the cluster DNS policy and resolv.conf inside pods, and ensuring that the DNS service is reachable from workloads. KubernetesDNS remains a core mechanism for internal name resolution and service discovery in Kubernetes.