# CoreDNS — Flexible DNS Server Written in Go

> CoreDNS is a CNCF-graduated DNS server written in Go, composed entirely of plugins, and used as the default in-cluster DNS for Kubernetes since v1.13.

## Install

Save as a script file and run:

# CoreDNS — Flexible DNS Server Written in Go

## Quick Use
```bash
# Grab a release binary and serve a zone
curl -LO https://github.com/coredns/coredns/releases/latest/download/coredns_linux_amd64.tgz
tar xzf coredns_linux_amd64.tgz

cat > Corefile <<EOF2
.:1053 {
    forward . 1.1.1.1 8.8.8.8
    cache 30
    log
    errors
    prometheus :9153
}
EOF2
./coredns -conf ./Corefile

# Test with dig
dig @127.0.0.1 -p 1053 github.com +short
```

## Introduction
CoreDNS was created as a modern successor to SkyDNS and quickly replaced kube-dns as the Kubernetes cluster DNS default. Its killer idea is plugin composition: a small core plus a linkable chain of plugins (cache, forward, kubernetes, file, etcd, hosts, rewrite, acl, metrics, health) described in a Caddy-style `Corefile`.

## What CoreDNS Does
- Serves authoritative DNS from zone files, etcd, Kubernetes, or S3.
- Caches responses with configurable TTL floors/ceilings and pre-fetching.
- Forwards to upstream resolvers with health checks and policy-based selection.
- Resolves Kubernetes `Service` and `Pod` DNS records via the `kubernetes` plugin.
- Exports Prometheus metrics, OpenTelemetry traces, and structured logs.

## Architecture Overview
CoreDNS is a single Go binary built around the `dns.Handler` chain. Each plugin is a Go package that implements `ServeDNS` and optionally `Setup`; compiling CoreDNS with a different `plugin.cfg` produces a custom binary with only the plugins you need. The `Corefile` is parsed at start-up into server blocks, each with its own listen address, zones, and plugin chain, giving you per-zone DNS views without extra processes.

## Self-Hosting & Configuration
- Binary releases for Linux, macOS, Windows, FreeBSD, ARM64; Docker image `coredns/coredns`.
- Drive configuration with a single `Corefile` — edit and SIGUSR1 to reload without dropping queries.
- Use the `kubernetes` plugin for cluster DNS: point at the API and watch Services and Endpoints.
- Turn on DNSSEC via the `dnssec` plugin for signed outbound responses.
- Deploy multiple instances behind a VIP (keepalived, MetalLB, kube-proxy) for HA.

## Key Features
- Kubernetes-native: authoritative for `cluster.local` with fast label selectors and EndpointSlice support.
- Rich plugin ecosystem (60+) covering caching, security, rewriting, filtering, and service discovery.
- Zero-downtime reload of zones and Corefile changes.
- Prometheus metrics out of the box for QPS, cache hit rate, upstream latency, and errors.
- Small footprint — single static binary, <20 MB memory baseline.

## Comparison with Similar Tools
- **BIND9** — venerable and feature-rich but more complex to operate and less cloud-native.
- **Unbound** — recursive-focused, great caching resolver; CoreDNS additionally serves authoritative zones and K8s.
- **PowerDNS** — excellent authoritative + recursor split with many backends; CoreDNS trades SQL backends for plugin composability.
- **dnsmasq** — light and simple for home/lab; CoreDNS scales further with observability and Kubernetes integration.
- **Route53 / Cloud DNS** — managed services; CoreDNS lets you keep control and run anywhere.

## FAQ
**Q: Can I run CoreDNS outside Kubernetes?**
A: Yes — it works equally well as a standalone DNS server, caching resolver, or authoritative nameserver.

**Q: How do I add a custom plugin?**
A: Add the plugin to `plugin.cfg` in the source tree and `make` — CoreDNS uses `external-plugin` pattern via Caddy.

**Q: Does it support DNS-over-TLS / HTTPS?**
A: Yes, the `tls` directive enables DoT; the `grpc` and `forward https://...` options cover DoH upstreams.

**Q: How do I debug slow queries?**
A: Enable the `log` and `trace` plugins, scrape Prometheus latency histograms, and ship spans to Jaeger or Tempo.

## Sources
- https://github.com/coredns/coredns
- https://coredns.io


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Source: https://tokrepo.com/en/workflows/e0db27a2-38ce-11f1-9bc6-00163e2b0d79
Author: Script Depot