coredns

command module
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 Go to latest Published: May 10, 2022 License: Apache-2.0 Imports: 2 Imported by: 0

README

CoreDNS

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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 (RFC 7858), also called DoT, DNS over HTTP/2 - DoH - (RFC 8484) 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 + 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.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).
  • 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.

Compilation from Source

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 1.17 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.

Compilation with Docker

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:1.17 make

The above command alone will have coredns binary generated.

Examples

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, aa8c32

The following could be used to query the CoreDNS server that is running now:

dig @127.0.0.1 -p 53 www.example.com

Any 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.txt

You 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
}

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.

Community

We're most active on Github (and Slack):

More resources can be found:

Contribution guidelines

If you want to contribute to CoreDNS, be sure to review the contribution guidelines.

Deployment

Examples for deployment via systemd and other use cases can be found in the deployment repository.

Deprecation Policy

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.

Security

Security Audits

Third party security audits have been performed by:

Reporting security vulnerabilities

If you find a security vulnerability or any security related issues, please DO NOT file a public issue, instead send your report privately to security@coredns.io. 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

Documentation

The Go Gopher

There is no documentation for this package.

Source Files

View all Source files

Directories

Path Synopsis
Package core registers the server and all plugins we support.
 Package core registers the server and all plugins we support.
dnsserver
Package dnsserver implements all the interfaces from Caddy, so that CoreDNS can be a servertype plugin.
 Package dnsserver implements all the interfaces from Caddy, so that CoreDNS can be a servertype plugin.
plugin
Package coremain contains the functions for starting CoreDNS.
 Package coremain contains the functions for starting CoreDNS.
Package plugin provides some types and functions common among plugin.
 Package plugin provides some types and functions common among plugin.
acl
any
auto
Package auto implements an on-the-fly loading file backend.
 Package auto implements an on-the-fly loading file backend.
autopath
Package autopath implements autopathing.
 Package autopath implements autopathing.
azure
bind
Package bind allows binding to a specific interface instead of bind to all of them.
 Package bind allows binding to a specific interface instead of bind to all of them.
bufsize
Package bufsize implements a plugin that modifies EDNS0 buffer size.
 Package bufsize implements a plugin that modifies EDNS0 buffer size.
cache
Package cache implements a cache.
 Package cache implements a cache.
cache/freq
Package freq keeps track of last X seen events.
 Package freq keeps track of last X seen events.
cancel
Package cancel implements a plugin adds a canceling context to each request.
 Package cancel implements a plugin adds a canceling context to each request.
chaos
Package chaos implements a plugin that answer to 'CH version.bind TXT' type queries.
 Package chaos implements a plugin that answer to 'CH version.bind TXT' type queries.
clouddns
Package clouddns implements a plugin that returns resource records from GCP Cloud DNS.
 Package clouddns implements a plugin that returns resource records from GCP Cloud DNS.
debug
deprecated
Package deprecated is used when we deprecated plugin.
 Package deprecated is used when we deprecated plugin.
dns64
Package dns64 implements a plugin that performs DNS64.
 Package dns64 implements a plugin that performs DNS64.
dnssec
Package dnssec implements a plugin that signs responses on-the-fly using NSEC black lies.
 Package dnssec implements a plugin that signs responses on-the-fly using NSEC black lies.
dnstap
dnstap/msg
erratic
Package erratic implements a plugin that returns erratic answers (delayed, dropped).
 Package erratic implements a plugin that returns erratic answers (delayed, dropped).
errors
Package errors implements an error handling plugin.
 Package errors implements an error handling plugin.
etcd
Package etcd provides the etcd version 3 backend plugin.
 Package etcd provides the etcd version 3 backend plugin.
etcd/msg
Package msg defines the Service structure which is used for service discovery.
 Package msg defines the Service structure which is used for service discovery.
file
Package file implements a file backend.
 Package file implements a file backend.
file/rrutil
Package rrutil provides function to find certain RRs in slices.
 Package rrutil provides function to find certain RRs in slices.
file/tree
Package tree implements Left-Leaning Red Black trees as described by Robert Sedgewick.
 Package tree implements Left-Leaning Red Black trees as described by Robert Sedgewick.
forward
Package forward implements a forwarding proxy.
 Package forward implements a forwarding proxy.
geoip
Package geoip implements a max mind database plugin.
 Package geoip implements a max mind database plugin.
grpc
header
health
Package health implements an HTTP handler that responds to health checks.
 Package health implements an HTTP handler that responds to health checks.
hosts
k8s_external
Package external implements external names for kubernetes clusters.
 Package external implements external names for kubernetes clusters.
kubernetes
Package kubernetes provides the kubernetes backend.
 Package kubernetes provides the kubernetes backend.
kubernetes/object
Package object holds functions that convert the objects from the k8s API in to a more memory efficient structures.
 Package object holds functions that convert the objects from the k8s API in to a more memory efficient structures.
loadbalance
Package loadbalance is a plugin for rewriting responses to do "load balancing" Package loadbalance shuffles A, AAAA and MX records.
 Package loadbalance is a plugin for rewriting responses to do "load balancing" Package loadbalance shuffles A, AAAA and MX records.
local
log
Package log implements basic but useful request (access) logging plugin.
 Package log implements basic but useful request (access) logging plugin.
loop
metadata
Package metadata provides an API that allows plugins to add metadata to the context.
 Package metadata provides an API that allows plugins to add metadata to the context.
metrics
Package metrics implement a handler and plugin that provides Prometheus metrics.
 Package metrics implement a handler and plugin that provides Prometheus metrics.
metrics/vars
minimal
nsid
Package nsid implements NSID protocol
 Package nsid implements NSID protocol
pkg/cache
Package cache implements a cache.
 Package cache implements a cache.
pkg/cidr
Package cidr contains functions that deal with classless reverse zones in the DNS.
 Package cidr contains functions that deal with classless reverse zones in the DNS.
pkg/dnstest
Package dnstest allows for easy testing of DNS client against a test server.
 Package dnstest allows for easy testing of DNS client against a test server.
pkg/dnsutil
Package dnsutil contains DNS related helper functions.
 Package dnsutil contains DNS related helper functions.
pkg/doh
pkg/edns
Package edns provides function useful for adding/inspecting OPT records to/in messages.
 Package edns provides function useful for adding/inspecting OPT records to/in messages.
pkg/fall
Package fall handles the fallthrough logic used in plugins that support it.
 Package fall handles the fallthrough logic used in plugins that support it.
pkg/fuzz
Package fuzz contains functions that enable fuzzing of plugins.
 Package fuzz contains functions that enable fuzzing of plugins.
pkg/log
Package log implements a small wrapper around the std lib log package.
 Package log implements a small wrapper around the std lib log package.
pkg/nonwriter
Package nonwriter implements a dns.ResponseWriter that never writes, but captures the dns.Msg being written.
 Package nonwriter implements a dns.ResponseWriter that never writes, but captures the dns.Msg being written.
pkg/parse
Package parse contains functions that can be used in the setup code for plugins.
 Package parse contains functions that can be used in the setup code for plugins.
pkg/rand
Package rand is used for concurrency safe random number generator.
 Package rand is used for concurrency safe random number generator.
pkg/rcode
pkg/replacer
pkg/response
pkg/reuseport
pkg/singleflight
Package singleflight provides a duplicate function call suppression mechanism.
 Package singleflight provides a duplicate function call suppression mechanism.
pkg/tls
pkg/trace
pkg/transport
pkg/uniq
Package uniq keeps track of "thing" that are either "todo" or "done".
 Package uniq keeps track of "thing" that are either "todo" or "done".
pkg/up
Package up is used to run a function for some duration.
 Package up is used to run a function for some duration.
pkg/upstream
Package upstream abstracts a upstream lookups so that plugins can handle them in an unified way.
 Package upstream abstracts a upstream lookups so that plugins can handle them in an unified way.
pprof
Package pprof implements a debug endpoint for getting profiles using the go pprof tooling.
 Package pprof implements a debug endpoint for getting profiles using the go pprof tooling.
ready
Package ready is used to signal readiness of the CoreDNS process.
 Package ready is used to signal readiness of the CoreDNS process.
reload
Package reload periodically checks if the Corefile has changed, and reloads if so.
 Package reload periodically checks if the Corefile has changed, and reloads if so.
rewrite
Package rewrite is a plugin for rewriting requests internally to something different.
 Package rewrite is a plugin for rewriting requests internally to something different.
root
route53
Package route53 implements a plugin that returns resource records from AWS route53.
 Package route53 implements a plugin that returns resource records from AWS route53.
secondary
Package secondary implements a secondary plugin.
 Package secondary implements a secondary plugin.
sign
Package sign implements a zone signer as a plugin.
 Package sign implements a zone signer as a plugin.
template
test
Package test contains helper functions for writing plugin tests.
 Package test contains helper functions for writing plugin tests.
tls
trace
Package trace implements OpenTracing-based tracing
 Package trace implements OpenTracing-based tracing
transfer
whoami
Package whoami implements a plugin that returns details about the resolving querying it.
 Package whoami implements a plugin that returns details about the resolving querying it.
Package request abstracts a client's request so that all plugins will handle them in an unified way.
 Package request abstracts a client's request so that all plugins will handle them in an unified way.
Package test contains function and types useful for writing tests.
 Package test contains function and types useful for writing tests.

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