# Erlang DNS Server

Serve DNS authoritative responses...with Erlang.

[![Build Status](https://travis-ci.org/dnsimple/erl-dns.png?branch=master)](https://travis-ci.org/dnsimple/erl-dns)

## 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 use Foreman:

    foreman start

## 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:

```erlang
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