RubyDNS

Released under the MIT license.
Copyright (C) 2009, 2011 Samuel G. D. Williams.

RubyDNS is a simple programmatic DSL (domain specific language) for configuring and running a DNS server. RubyDNS provides a daemon that runs a DNS server which can process DNS requests depending on specific policy. Rule selection is based on pattern matching, and results can be hard-coded, computed, fetched from a remote DNS server, fetched from a local cache, etc.

RubyDNS provides a full daemon server using RExec. You can either use the built in daemon, customize it to your needs, or specify a full daemon implementation.

RubyDNS is not designed to be high-performance and uses a thread-per-request model. This is designed to make it as easy as possible to achieve concurrent performance. This is also due to the fact that many other APIs work best this way (unfortunately).

For examples please see the main project page.

Basic Example

This is copied from test/example1.rb. It has been simplified slightly.

require 'rubygems'
require 'rubydns'

$R = Resolv::DNS.new

RubyDNS::run_server do
    Name = Resolv::DNS::Name
    IN = Resolv::DNS::Resource::IN

    # For this exact address record, return an IP address
    match("dev.mydomain.org", IN::A) do |transaction|
        transaction.respond!("10.0.0.80")
    end

    match(/^test([0-9]+).mydomain.org$/, IN::A) do |match_data, transaction|
        offset = match_data[1].to_i

        if offset > 0 && offset < 10
            logger.info "Responding with address #{"10.0.0." + (90 + offset).to_s}..."
            transaction.respond!("10.0.0." + (90 + offset).to_s)
        else
            logger.info "Address out of range: #{offset}!"
            false
        end
    end

    # Default DNS handler
    otherwise do |transaction|
        logger.info "Passing DNS request upstream..."
        transaction.passthrough!($R)
    end
end

After starting this server you can test it using dig:

dig @localhost test1.mydomain.org
dig @localhost dev.mydomain.org
dig @localhost google.com

Compatibility

Migrating from RubyDNS 0.3.x to 0.4.x

Due to changes in resolv.rb, superficial parts of RubyDNS have changed. Rather than using :A to specify A-records, one must now use the class name.

match(..., :A)

becomes

IN = Resolv::DNS::Resource::IN
match(..., IN::A)

Migrating from RubyDNS 0.4.x to 0.5.x

The system standard resolver was synchronous, and this could stall the server when making upstream requests to other DNS servers. A new resolver RubyDNS::Resolver now provides an asynchronous interface and the Transaction::passthrough makes exclusive use of this to provide high performance asynchonous resolution.

Here is a basic example of how to use the new resolver in full. It is important to provide both :udp and :tcp connection specifications, so that large requests will be handled correctly:

resolver = RubyDNS::Resolver.new([[:udp, "8.8.8.8", 53], [:tcp, "8.8.8.8", 53]])

EventMachine::run do
    resolver.query('google.com', IN::A) do |response|
        case response
        when RubyDNS::Message
            puts "Got response: #{response.answers.first}"
        else
            # Response is of class RubyDNS::ResolutionFailure
            puts "Failed: #{response.message}"
        end

        EventMachine::stop
    end
end

Existing code that uses Resolv::DNS as a resolver will need to be updated:

# 1/ Add this at the top of your file; Host specific system information:
require 'rubydns/system'

# 2/ Change from R = Resolv::DNS.new to:
R = RubyDNS::Resolver.new(RubyDNS::System::nameservers)

Everything else in the server can remain the same. You can see a complete example in test/test_resolver.rb.

Deferred Transactions

The implementation of the above depends on a new feature which was added in 0.5.0:

transaction.defer!

Once you call this, the transaction won't complete until you call either transaction.succeed or transaction.fail.

RubyDNS::run_server(:listen => SERVER_PORTS) do
    match(/\.*.com/, IN::A) do |match, transaction|
        transaction.defer!

        # No domain exists, after 5 seconds:
        EventMachine::Timer.new(5) do
            transaction.failure!(:NXDomain)
        end
    end

    otherwise do
        transaction.failure!(:NXDomain)
    end
end

You can see a complete example in test/test_slow_server.rb.

Todo

Support for more features of DNS such as zone transfer.
Support reverse records more easily.

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.