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CoreDNS

CoreDNS is DNS server that started as a fork of Caddy. It has the same model: it chains middleware.

CoreDNS is the successor of SkyDNS. SkyDNS is a thin layer that exposes services in etcd in the DNS. CoreDNS builds on this idea and is a generic DNS server that can talk to multiple backends (etcd, consul, kubernetes, etc.).

CoreDNS aims to be a fast and flexible DNS server. The keyword here is flexible, with CoreDNS you are able to do what you want with your DNS data. And if not: write a middleware!

Currently CoreDNS is able to:

  • Serve zone data from a file, both DNSSEC (NSEC only) and DNS is supported (middleware/file).
  • Retrieve zone data from primaries, i.e. act as a secondary server (AXFR only) (middleware/secondary).
  • Sign zone data on-the-fly (middleware/dnssec).
  • Loadbalancing of responses (middleware/loadbalance).
  • Allow for zone transfers, i.e. act as a primary server (middleware/file).
  • Caching (middleware/cache).
  • Health checking (middleware/health).
  • Use etcd as a backend, i.e. a 101.5% replacement for SkyDNS (middleware/etcd).
  • Use k8s (kubernetes) as a backend (middleware/kubernetes).
  • Serve as a proxy to forward queries to some other (recursive) nameserver (middleware/proxy).
  • Rewrite queries (both qtype, qclass and qname) (middleware/rewrite).
  • Provide metrics (by using Prometheus) (middleware/metrics).
  • Provide Logging (middleware/log).
  • Has support for the CH class: version.bind and friends (middleware/chaos).
  • Profiling support (middleware/pprof).

Status

I'm using CoreDNS is my primary, authoritative, nameserver for my domains (miek.nl, atoom.net and a few others). CoreDNS should be stable enough to provide you with a good DNS(SEC) service.

There are still few issues, and work is ongoing on making things fast and reduce the memory usage.

All in all, CoreDNS should be able to provide you with enough functionality to replace parts of BIND9, Knot, NSD or PowerDNS. Most documentation is in the source and some blog articles can be found here. If you do want to use CoreDNS in production, please let us know and how we can help.

https://caddyserver.com/ is also full of examples on how to structure a Corefile (renamed from Caddyfile when I forked it).

Examples

Start a simple proxy:

Corefile contains:

.:1053 {
    proxy . 8.8.8.8:53
}

Just start CoreDNS: ./coredns. And then just query on that port (1053), the query should be forwarded to 8.8.8.8 and the response will be returned.

Serve the (NSEC) DNSSEC signed miek.nl on port 1053, errors and logging to stdout. Allow zone transfers to everybody.

miek.nl:1053 {
    file /var/lib/bind/miek.nl.signed {
        transfer to *
    }
    errors stdout
    log stdout
}

Serve miek.nl on port 1053, but forward everything that does not match miek.nl to a recursive nameserver and rewrite ANY queries to HINFO.

.:1053 {
    rewrite ANY HINFO
    proxy . 8.8.8.8:53

    file /var/lib/bind/miek.nl.signed miek.nl {
        transfer to *
    }
    errors stdout
    log stdout
}

All the above examples are possible with the current CoreDNS.

What remains to be done

  • Website?
  • Logo?
  • Optimizations.
  • Load testing.
  • The issues.

Blog

https://miek.nl/tags/coredns/

Systemd service file

Use this as a systemd service file. It defaults to a coredns wich a homedir of /home/coredns and the binary lives in /opt/bin:

[Unit]
Description=CoreDNS DNS server
Documentation=https://miek.nl/tags/coredns
After=network.target

[Service]
PermissionsStartOnly=true
PIDFile=/home/coredns/coredns.pid
LimitNOFILE=8192
User=coredns
WorkingDirectory=/home/coredns
ExecStartPre=/sbin/setcap cap_net_bind_service=+ep /opt/bin/coredns
ExecStart=/opt/bin/coredns -pidfile /home/coredns/coredns.pid -conf=/etc/coredns
ExecReload=/bin/kill -SIGUSR1 $MAINPID
Restart=on-failure

[Install]
WantedBy=multi-user.target