CoreDNS is a DNS server/forwarder, written in Go, that chains plugins. Each plugin performs a (DNS) function.
CoreDNS is a Cloud Native Computing Foundation graduated project.
CoreDNS is a fast and flexible DNS server. The key word here is flexible: with CoreDNS you are able to do what you want with your DNS data by utilizing plugins. If some functionality is not provided out of the box you can add it by writing a plugin.
CoreDNS can listen for DNS requests coming in over:
- UDP/TCP (go'old DNS).
- TLS - DoT (RFC 7858).
- DNS over HTTP/2 - DoH (RFC 8484).
- DNS over QUIC - DoQ (RFC 9250).
- gRPC (not a standard).
Currently CoreDNS is able to:
- Serve zone data from a file; both DNSSEC (NSEC only) and DNS are supported (file and auto).
- Retrieve zone data from primaries, i.e., act as a secondary server (AXFR only) (secondary).
- Sign zone data on-the-fly (dnssec).
- Load balancing of responses (loadbalance).
- Allow for zone transfers, i.e., act as a primary server (file + transfer).
- Automatically load zone files from disk (auto).
- Caching of DNS responses (cache).
- Use etcd as a backend (replacing SkyDNS) (etcd).
- Use k8s (kubernetes) as a backend (kubernetes).
- Serve as a proxy to forward queries to some other (recursive) nameserver (forward).
- Provide metrics (by using Prometheus) (prometheus).
- Provide query (log) and error (errors) logging.
- Integrate with cloud providers (route53).
- Support the CH class:
version.bindand friends (chaos). - Support the RFC 5001 DNS name server identifier (NSID) option (nsid).
- Profiling support (pprof).
- Rewrite queries (qtype, qclass and qname) (rewrite and template).
- Block ANY queries (any).
- Provide DNS64 IPv6 Translation (dns64).
And more. Each of the plugins is documented. See coredns.io/plugins for all in-tree plugins, and coredns.io/explugins for all out-of-tree plugins.
To compile CoreDNS, we assume you have a working Go setup. See various tutorials if you don’t have that already configured.
First, make sure your golang version is 1.20 or higher as go mod support and other api is needed.
See here for go mod details.
Then, check out the project and run make to compile the binary:
$ git clone https://github.com/coredns/coredns
$ cd coredns
$ make
This should yield a coredns binary.
CoreDNS requires Go to compile. However, if you already have docker installed and prefer not to setup a Go environment, you could build CoreDNS easily:
$ docker run --rm -i -t -v $PWD:/v -w /v golang:1.21 make
The above command alone will have coredns binary generated.
When starting CoreDNS without any configuration, it loads the
whoami and log plugins
and starts listening on port 53 (override with -dns.port), it should show the following:
.:53
CoreDNS-1.6.6
linux/amd64, go1.16.10, aa8c32The following could be used to query the CoreDNS server that is running now:
dig @127.0.0.1 -p 53 www.example.comAny query sent to port 53 should return some information; your sending address, port and protocol used. The query should also be logged to standard output.
The configuration of CoreDNS is done through a file named Corefile. When CoreDNS starts, it will
look for the Corefile from the current working directory. A Corefile for CoreDNS server that listens
on port 53 and enables whoami plugin is:
.:53 {
whoami
}
Sometimes port number 53 is occupied by system processes. In that case you can start the CoreDNS server
while modifying the Corefile as given below so that the CoreDNS server starts on port 1053.
.:1053 {
whoami
}
If you have a Corefile without a port number specified it will, by default, use port 53, but you can
override the port with the -dns.port flag: coredns -dns.port 1053, runs the server on port 1053.
You may import other text files into the Corefile using the import directive. You can use globs to match multiple
files with a single import directive.
.:53 {
import example1.txt
}
import example2.txtYou can use environment variables in the Corefile with {$VARIABLE}. Note that each environment variable is inserted
into the Corefile as a single token. For example, an environment variable with a space in it will be treated as a single
token, not as two separate tokens.
.:53 {
{$ENV_VAR}
}A Corefile for a CoreDNS server that forward any queries to an upstream DNS (e.g., 8.8.8.8) is as follows:
.:53 {
forward . 8.8.8.8:53
log
}
Start CoreDNS and then query on that port (53). The query should be forwarded to 8.8.8.8 and the response will be returned. Each query should also show up in the log which is printed on standard output.
To serve the (NSEC) DNSSEC-signed example.org on port 1053, with errors and logging sent to standard
output. Allow zone transfers to everybody, but specifically mention 1 IP address so that CoreDNS can
send notifies to it.
example.org:1053 {
file /var/lib/coredns/example.org.signed
transfer {
to * 2001:500:8f::53
}
errors
log
}Serve example.org on port 1053, but forward everything that does not match example.org to a
recursive nameserver and rewrite ANY queries to HINFO.
example.org:1053 {
file /var/lib/coredns/example.org.signed
transfer {
to * 2001:500:8f::53
}
errors
log
}
. {
any
forward . 8.8.8.8:53
errors
log
}IP addresses are also allowed. They are automatically converted to reverse zones:
10.0.0.0/24 {
whoami
}
Means you are authoritative for 0.0.10.in-addr.arpa..
This also works for IPv6 addresses. If for some reason you want to serve a zone named 10.0.0.0/24
add the closing dot: 10.0.0.0/24. as this also stops the conversion.
This even works for CIDR (See RFC 1518 and 1519) addressing, i.e. 10.0.0.0/25, CoreDNS will then
check if the in-addr request falls in the correct range.
Listening on TLS (DoT) and for gRPC? Use:
tls://example.org grpc://example.org {
whoami
}
Similarly, for QUIC (DoQ):
quic://example.org {
whoami
tls mycert mykey
}
And for DNS over HTTP/2 (DoH) use:
https://example.org {
whoami
tls mycert mykey
}
in this setup, the CoreDNS will be responsible for TLS termination
you can also start DNS server serving DoH without TLS termination (plain HTTP), but beware that in such scenario there has to be some kind of TLS termination proxy before CoreDNS instance, which forwards DNS requests otherwise clients will not be able to communicate via DoH with the server
https://example.org {
whoami
}
Specifying ports works in the same way:
grpc://example.org:1443 https://example.org:1444 {
# ...
}When no transport protocol is specified the default dns:// is assumed.
We're most active on Github (and Slack):
- Github: https://github.com/coredns/coredns
- Slack: #coredns on https://slack.cncf.io
More resources can be found:
- Website: https://coredns.io
- Blog: https://coredns.io/blog/
- Twitter: @corednsio
- Mailing list/group: [email protected] (not very active)
If you want to contribute to CoreDNS, be sure to review the contribution guidelines.
Examples for deployment via systemd and other use cases can be found in the deployment repository.
When there is a backwards incompatible change in CoreDNS the following process is followed:
- Release x.y.z: Announce that in the next release we will make backward incompatible changes.
- Release x.y+1.0: Increase the minor version and set the patch version to 0. Make the changes, but allow the old configuration to be parsed. I.e. CoreDNS will start from an unchanged Corefile.
- Release x.y+1.1: Increase the patch version to 1. Remove the lenient parsing, so CoreDNS will not start if those features are still used.
E.g. 1.3.1 announce a change. 1.4.0 a new release with the change but backward compatible config. And finally 1.4.1 that removes the config workarounds.
Third party security audits have been performed by:
- Cure53 in March 2018. Full Report
- Trail of Bits in March 2022. Full Report
If you find a security vulnerability or any security related issues, please DO NOT file a public
issue, instead send your report privately to [email protected]. Security reports are greatly
appreciated and we will publicly thank you for it.
Please consult security vulnerability disclosures and security fix and release process document