coredns

CoreDNS is an open-source DNS server written in Go that provides a flexible, plugin-based framework for DNS resolution and service discovery. It can function as an authoritative server, a caching resolver, or a forwarder, and is widely used as the DNS backend in Kubernetes environments as well as in traditional DNS deployments.

CoreDNS is configured with a Corefile, a plain text file that defines a chain of plugins to handle queries for one or more zones. Each plugin in the chain can answer, modify, or forward requests. This plugin architecture enables CoreDNS to support standard DNS features and to be extended for custom use cases without rewriting core logic.

In Kubernetes, CoreDNS serves as the cluster DNS service. It integrates with the Kubernetes API to publish service and pod names as DNS records via the kubernetes plugin and can forward unresolved queries to upstream resolvers. CoreDNS is container-friendly and commonly deployed as a pod within the cluster, scaling alongside workloads.

Notable plugins include kubernetes, file, etcd, forward, cache, rewrite, template, whoami, log, errors, and metrics. CoreDNS is released under the Apache 2.0 license and is maintained as a community-driven project with contributions from individuals and organizations; it is a prominent member of the cloud-native and CNCF ecosystems.