CoreDNS (written in Go) 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 keyword 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 (RFC 7858) and 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).
- Automatically load zone files from disk (auto).
- Caching (cache).
- Use etcd as a backend (replace 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) (metrics).
- Provide query (log) and error (errors) logging.
- Support the CH class:
version.bind
and 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).
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 1.12 or higher as go mod
support 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:/go/src/github.com/coredns/coredns \
-w /go/src/github.com/coredns/coredns golang:1.12 make
The above command alone will have coredns
binary generated.
When starting CoreDNS without any configuration, it loads the
whoami plugin and starts listening on port 53 (override with
-dns.port
), it should show the following:
.:53
2016/09/18 09:20:50 [INFO] CoreDNS-001
CoreDNS-001
Any query sent to port 53 should return some information; your sending address, port and protocol used.
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.
Start a simple proxy. You'll need to be root to start listening on port 53.
Corefile
contains:
.:53 {
forward . 8.8.8.8:53
log
}
Just start CoreDNS: ./coredns
. Then just 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.
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 *
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.
.:1053 {
rewrite ANY HINFO
forward . 8.8.8.8:53
file /var/lib/coredns/example.org.signed example.org {
transfer to *
transfer to 2001:500:8f::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 and for gRPC? Use:
tls://example.org grpc://example.org {
whoami
}
Specifying ports works in the same way:
grpc://example.org:1443 {
# ...
}
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://blog.coredns.io
- Twitter: @corednsio
- Mailing list/group: [email protected] (not very active)
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.
A third party security audit was performed by Cure53, you can see the full report here.
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