Erlang DNS Server

Serve DNS authoritative responses...with Erlang.

Building

To build:

make

To start fresh:

make fresh make

Zones

Zones are loaded from JSON.

Example JSON files are in the priv/ directory.

You can also write new systems to load zones by writing the zones directly to the zone cache using erldns_zone_cache:put_zone/1.

Configuration

An example configuration file can be found in erldns.config.example.

Copy it to erldns.config and modify as needed.

Running

Launch directly:

rebar3 shell

Or build a distribution with rebar3 release and run the release:

./_build/default/rel/erldns/bin/erldns foreground

Querying

Here are some queries to try:

dig -p8053 @127.0.0.1 example.com a
dig -p8053 @127.0.0.1 example.com cname
dig -p8053 @127.0.0.1 example.com ns
dig -p8053 @127.0.0.1 example.com mx
dig -p8053 @127.0.0.1 example.com spf
dig -p8053 @127.0.0.1 example.com txt
dig -p8053 @127.0.0.1 example.com sshfp
dig -p8053 @127.0.0.1 example.com soa
dig -p8053 @127.0.0.1 example.com naptr

dig -p8053 @127.0.0.1 -x 127.0.0.1 ptr

Performance

In our environment (DNSimple) we are seeing 30 to 65 µs handoff times to retreive a packet from the UDP port and give it to a worker for processing. Your performance may vary, but given those measurements erl-dns is capable of handling between 15k and 30k questions per second. Please note: You may need to configure the number of workers available to handle traffic at higher volumes.

Design

The erldns_resolver module will attempt to find zone data in the zone cache. If you're embedding erl-dns in your application the easiest thing to do is to load the zone cache once the zone cache gen_server starts push an updated zone into the cache each time data changes.

To insert a zone, use erldns_zone_cache:put_zone({Name, Records}) where Name is a binary term such as <<"example.com">> and Records is a list of dns_rr records (whose definitions can be found in deps/dns/include/dns_records.hrl). The name of each record must be the fully qualified domain name (including the zone part).

Here's an example:

erldns_zone_cache:put_zone({
  <<"example.com">>, [
    #dns_rr{
      name = <<"example.com">>,
      type = ?DNS_TYPE_A,
      ttl = 3600,
      data = #dns_rrdata_a{ip = {1,2,3,4}}
    },
    #dns_rr{
      name = <<"www.example.com">>,
      type = ?DNS_TYPE_CNAME,
      ttl = 3600,
      data = #dns_rrdata_cname{dname = <<"example.com">>}
    }
  ]}).

Metrics

Folsom is used to gather runtime metrics and statistics.

There is an HTTP API for querying metric data available at https://github.com/dnsimple/erldns-metrics

Admin

There is a administrative API for querying the current zone cache and for basic control. You can find it in https://github.com/dnsimple/erldns-admin