CoreDNS is a fast, flexible, and extensible DNS server that can serve as a cluster DNS for Kubernetes. Written in Go, it is designed to be a modular and pluggable DNS server, where functionality is provided through a chain of plugins. These plugins can be configured and chained together to provide various DNS features, such as service discovery, load balancing, and external service resolution.
CoreDNS is valuable because it offers a highly customizable and scalable solution for managing DNS within containerized environments. Its integration with Kubernetes simplifies service discovery and provides a robust and reliable way for applications to resolve service names. Main use cases include Kubernetes cluster DNS, service discovery in cloud-native architectures, and general-purpose DNS server replacement.
CoreDNS is a cloud-native DNS server that focuses on flexibility through a unique plugin-based architecture. It is the default DNS server for Kubernetes.
Plugin Architecture
The core strength of CoreDNS lies in its plugins. Every feature, from serving a zone file to caching responses to Kubernetes service discovery, is implemented as a middleware plugin. This means:
- Extensibility: You can easily write custom plugins to handle specific DNS logic.
- Efficiency: You only load the plugins you need.
- Chaining: Plugins are chained together; a request passes through the chain until a plugin handles it.
Key Plugins
kubernetes: Serves DNS records for Kubernetes Services and Pods.etcd: Serves records stored in an etcd cluster.promethus: Exposes metrics for Prometheus monitoring.cache: Caches DNS responses to improve performance.forward: Forwards queries to upstream DNS servers (like 8.8.8.8).