# Erlang DNS Server
Serve DNS authoritative responses... with Erlang.
[](https://github.com/dnsimple/erldns/actions/workflows/ci.yml)
[](https://hex.pm/packages/erldns)
## Requirements
Erlang/OTP 27+
## Building
To build:
```shell
make
```
To start fresh:
```shell
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
```shell
overmind start
```
### To get an interactive Erlang REPL
```shell
./rebar3 shell
```
### Build a distribution with and run the release
```shell
./rebar3 release
./_build/default/rel/erldns/bin/erldns foreground
```
## Querying
Here are some queries to try:
```bash
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`](./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:
```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">>}
}
]}).
```
### 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 at <https://github.com/dnsimple/erldns-metrics>
## Admin
There is an administrative API for querying the current zone cache and for basic control. You can find it in <https://github.com/dnsimple/erldns-admin>.
## Tests
To run automated tests:
```shell
make test
```
This runs both [EUnit](https://www.erlang.org/doc/apps/eunit/chapter.html) tests and [dialyzer](https://www.erlang.org/docs/23/man/dialyzer.html).
