etcd

etcd enables reading zone data from an etcd instance.

Description

The data in etcd has to be encoded as a message like SkyDNS. It should also work just like SkyDNS.

The etcd plugin makes extensive use of the proxy plugin to forward and query other servers in the network.

Syntax

etcd [ZONES...]
  • ZONES zones etcd should be authoritative for.

The path will default to /skydns the local etcd proxy (http://localhost:2379). If no zones are specified the block’s zone will be used as the zone.

If you want to round robin A and AAAA responses look at the loadbalance plugin.

etcd [ZONES...] {
    stubzones
    fallthrough [ZONES...]
    path PATH
    endpoint ENDPOINT...
    upstream [ADDRESS...]
    tls CERT KEY CACERT
}
  • stubzones enables the stub zones feature. The stubzone is only done in the etcd tree located under the first zone specified.
  • fallthrough If zone matches but no record can be generated, pass request to the next plugin. If [ZONES…] is omitted, then fallthrough happens for all zones for which the plugin is authoritative. If specific zones are listed (for example in-addr.arpa and ip6.arpa), then only queries for those zones will be subject to fallthrough.
  • PATH the path inside etcd. Defaults to “/skydns”.
  • ENDPOINT the etcd endpoints. Defaults to “http://localhost:2379".
  • upstream upstream resolvers to be used resolve external names found in etcd (think CNAMEs) pointing to external names. If you want CoreDNS to act as a proxy for clients, you’ll need to add the proxy plugin. If no ADDRESS is given, CoreDNS will resolve CNAMEs against itself. ADDRESS can be an IP address, and IP:port or a string pointing to a file that is structured as /etc/resolv.conf.
  • tls followed by:

    • no arguments, if the server certificate is signed by a system-installed CA and no client cert is needed
    • a single argument that is the CA PEM file, if the server cert is not signed by a system CA and no client cert is needed
    • two arguments - path to cert PEM file, the path to private key PEM file - if the server certificate is signed by a system-installed CA and a client certificate is needed
    • three arguments - path to cert PEM file, path to client private key PEM file, path to CA PEM file - if the server certificate is not signed by a system-installed CA and client certificate is needed.

Examples

This is the default SkyDNS setup, with everying specified in full:

. {
    etcd skydns.local {
        stubzones
        path /skydns
        endpoint http://localhost:2379
        upstream 8.8.8.8:53 8.8.4.4:53
    }
    prometheus
    cache 160 skydns.local
    loadbalance
    proxy . 8.8.8.8:53 8.8.4.4:53
}

Or a setup where we use /etc/resolv.conf as the basis for the proxy and the upstream when resolving external pointing CNAMEs.

. {
    etcd skydns.local {
        path /skydns
        upstream /etc/resolv.conf
    }
    cache 160 skydns.local
    proxy . /etc/resolv.conf
}

Multiple endpoints are supported as well.

etcd skydns.local {
    endpoint http://localhost:2379 http://localhost:4001
...

Reverse zones

Reverse zones are supported. You need to make CoreDNS aware of the fact that you are also authoritative for the reverse. For instance if you want to add the reverse for 10.0.0.0/24, you’ll need to add the zone 0.0.10.in-addr.arpa to the list of zones. Showing a snippet of a Corefile:

etcd skydns.local 10.0.0.0/24 {
    stubzones
...

Next you’ll need to populate the zone with reverse records, here we add a reverse for 10.0.0.127 pointing to reverse.skydns.local.

% curl -XPUT http://127.0.0.1:4001/v2/keys/skydns/arpa/in-addr/10/0/0/127 \
    -d value='{"host":"reverse.skydns.local."}'

Querying with dig:

% dig @localhost -x 10.0.0.127 +short
reverse.skydns.local.

Zone name as A record

The zone name itself can be used A record. This behavior can be achieved by writing special entries to the ETCD path of your zone. If your zone is named skydns.local for example, you can create an A record for this zone as follows:

% curl -XPUT http://127.0.0.1:2379/v2/keys/skydns/local/skydns/dns/apex -d value='{"host":"1.1.1.1","ttl":"60"}'

If you query the zone name itself, you will receive the created A record:

% dig +short skydns.local @localhost
1.1.1.1

If you would like to use DNS RR for the zone name, you can set the following:

% curl -XPUT http://127.0.0.1:2379/v2/keys/skydns/local/skydns/dns/apex/x1 -d value='{"host":"1.1.1.1","ttl":"60"}'
% curl -XPUT http://127.0.0.1:2379/v2/keys/skydns/local/skydns/dns/apex/x2 -d value='{"host":"1.1.1.2","ttl":"60"}'

If you query the zone name now, you will get the following response:

dig +short skydns.local @localhost
1.1.1.1
1.1.1.2

If you would like to use AAAA records for the zone name too, you can set the following:

% curl -XPUT http://127.0.0.1:2379/v2/keys/skydns/local/skydns/dns/apex/x3 -d value='{"host":"2003::8:1","ttl":"60"}'
% curl -XPUT http://127.0.0.1:2379/v2/keys/skydns/local/skydns/dns/apex/x4 -d value='{"host":"2003::8:2","ttl":"60"}'

If you query the zone name now for AAAA now, you will get the following response:

dig +short skydns.local AAAA @localhost
2003::8:1
2003::8:2

Bugs

Only the etcdv2 protocol is supported.