In-Depth Understanding of CoreDNS

1. Core Concepts

CoreDNS is a flexible and extensible DNS server that graduated from the CNCF (Cloud Native Computing Foundation). It is written in Go and built on the Caddy server framework. CoreDNS adopts a plugin-based architecture, enabling users to customize DNS services via the Corefile configuration.

Core Architecture

Key components of CoreDNS include:

1. 1. Server — Listens for and handles DNS queries.
2. 2. Plugin Chain — Each DNS query is processed through a series of plugins.
3. 3. Corefile — Configuration file defining DNS zones and plugin chains.

Workflow

1. 1. When CoreDNS receives a DNS query, it matches the query to the corresponding domain defined in the Corefile.
2. 2. The query flows through the configured plugin chain.
3. 3. If a plugin can resolve the query, it returns a response to the client.
4. 4. If none of the plugins can resolve the query, CoreDNS returns SERVFAIL or forwards the query to an upstream DNS server if configured.

Key Plugins

Popular CoreDNS plugins include:

• file – Loads DNS records from zone files.
• auto – Automatically loads zone files from disk.
• etcd / kubernetes – Retrieves records from etcd or Kubernetes APIs.