geodns

GeoDNS in Go

This is the DNS server powering the NTP Pool system and other similar services. It supersedes the pgeodns server.

Installation

If you already have go installed, just run go get to install the Go dependencies.

You will also need the GeoIP C library, on RedHat derived systems that's yum install geoip-devel.

If you don't have Go installed the easiest way to build geodns from source is to download Go from http://code.google.com/p/go/downloads/list and untar'ing it in /usr/local/go and then run the following from a regular user account:

export PATH=$PATH:/usr/local/go/bin
export GOPATH=~/go
go get github.com/abh/geodns
cd ~/go/src/github.com/abh/geodns
go test
go build

Sample configuration

There's a sample configuration file in dns/example.com.json. This is currently derived from the test.example.com data used for unit tests and not an example of a "best practices" configuration.

For testing there's also a bigger test file at:

mkdir -p dns
curl -o dns/test.ntppool.org.json http://tmp.askask.com/2012/08/dns/ntppool.org.json.big

Run it

go run *.go -log -interface 127.1 -port 5053

or if you already built geodns, then ./geodns ....

To test the responses run

dig -t a test.example.com @127.1 -p 5053

Command options

Notable command line parameters (and their defaults)

• -config="./dns/"

Directory of zone files (and configuration named geodns.conf).

• -checkconfig=false

Check configuration file, parse zone files and exit

• -interface="*"

Comma separated IPs to listen on for DNS requests.

• -port="53"

Port number for DNS requests (UDP and TCP)

• -http=":8053"

Listen address for HTTP interface. Specify as 127.0.0.1:8053 to only listen on localhost.

• -identifier=""

Identifier for this instance (hostname, pop name or similar).

It can also be a comma separated list of identifiers where the first is the "server id" and subsequent ones are "group names", for example region of the server, name of anycast cluster the server is part of, etc. This is used in (future) reporting/statistics features.

• -log=false

Enable to get lots of extra logging, only useful for testing and debugging.

WebSocket interface

geodns runs a WebSocket server on port 8053 that outputs various performance metrics, see monitor.go for details.

Country and continent lookups

Weighted records

Except for NS records all records can have a 'weight' assigned. If any records of a particular type for a particular name have a weight, the system will return the "max_hosts" records (default 2)

Configuration format

In the configuration file the whole zone is a big hash (associative array). At the top level you can (optionally) set some options with the keys serial, ttl and max_hosts.

The actual zone data (dns records) is in a hash under the key "data". The keys in the hash are hostnames and the value for each hostname is yet another hash where the keys are record types (lowercase) and the values an array of records.

For example to setup an MX record at the zone apex and then have a different A record for users in Europe than anywhere else, use:

{
    "serial": 1,
    "data": {
        "": { "mx": { "mx": "mail.example.com", "preference": 10 } },
        "mail": { "a": [ ["192.168.0.1", 100], ["192.168.10.1", 50] ] },
        "mail.europe": { "a": [ ["192.168.255.1", 0] ] },
        "smtp": { "alias": "mail" }
    }
}

The configuration files are automatically reloaded when they're updated. If a file can't be read (invalid JSON, for example) the previous configuration for that zone will be kept.

Supported record types

A

Each record has the format of a short array with the first element being the IP address and the second the weight.

{ "a": [ [ "192.168.0.1", 10], ["192.168.2.1", 5] ] }

AAAA

Same format as A records (except the record type is "aaaa").

CNAME

The target will have the current zone name appended if it's not a FQDN (since v2.2.0).

{ "cname": "target.example.com." } { "cname": "www" }

NS

MX

{ "mx": "foo.example.com" }

Alias

Internally resolved cname, of sorts. Only works internally in a zone.

{ "alias": "foo" }

License and Copyright

This software is Copyright 2012-2013 Ask Bjørn Hansen. For licensing information please see the file called LICENSE.