Erlang DNS Server

Serve DNS authoritative responses... with Erlang.

Requirements

Erlang/OTP 27+

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.example.config. Copy it to erldns.config and modify as needed.

Running

Launch directly

overmind start

To get an interactive Erlang REPL

./rebar3 shell

Build a distribution with and run the release

./rebar3 release
./_build/default/rel/erldns/bin/erldns foreground

Querying

Here are some queries to try:

dig -p 8053 @127.0.0.1 example.com a
dig -p 8053 @127.0.0.1 example.com cname
dig -p 8053 @127.0.0.1 example.com ns
dig -p 8053 @127.0.0.1 example.com mx
dig -p 8053 @127.0.0.1 example.com spf
dig -p 8053 @127.0.0.1 example.com txt
dig -p 8053 @127.0.0.1 example.com sshfp
dig -p 8053 @127.0.0.1 example.com soa
dig -p 8053 @127.0.0.1 example.com naptr

dig -p 8053 @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 retrieve 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.

If you want to perform some benchmarks, see BENCHMARKING.md.

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">>}
    }
  ]}).

AXFR Support

AXFR zone transfers are not currently implemented. The current "implementation" is just a stub.

Metrics

Folsom is used to gather runtime metrics and statistics.

There is an HTTP API for querying metric data available, you can read more about it at m:erldns_metrics

Here's an example script that shows how to get the output with curl and pass it through Python to format it in a pretty fashion. It assumes you have this API running on port 8082.

curl -s http://localhost:8082/ -H "Accept: application/json" | python -mjson.tool

Important

Timing stats are given in microseconds.

Admin

There is an administrative API for querying the current zone cache and for basic control. You can read more about it at m:erldns_admin.

Tests

To run automated tests:

make test

This runs both EUnit tests and dialyzer.