Added support for upstream nameservers.

Previously, upstream nameservers were configured by default even if the
config file did not specify them. Now upstream nameservers are only
used if they are specified. If none are given, then NXDOMAIN is
returned for unresolvable requests.

extensions/dns/api.rb

@@ -34,38 +34,25 @@ def self.pre_http_start(http_hook_server)
             port = dns_config['port'] || 5300
             interfaces = [[protocol, address, port]]
 
-            Thread.new { EventMachine.next_tick { dns.run(:listen => interfaces) } }
-
-            print_info "DNS Server: #{address}:#{port} (#{protocol})"
-
-            # @todo Upstream servers are not yet supported. Uncomment this section when they are.
-=begin
             servers = []
+            upstream_servers = ''
 
-            unless dns_config['upstream'].nil?
+            unless dns_config['upstream'].nil? || dns_config['upstream'].empty?
               dns_config['upstream'].each do |server|
-                next if server[1].nil? or server[2].nil?
+                up_protocol = server[0].downcase
+                up_address = server[1]
+                up_port = server[2]
 
-                if server[0] == 'tcp'
-                  servers << ['tcp', server[1], server[2]]
-                elsif server[0] == 'udp'
-                  servers << ['udp', server[1], server[2]]
-                end
+                next if [up_protocol, up_address, up_port].include?(nil)
+                servers << [up_protocol.to_sym, up_address, up_port] if up_protocol =~ /^(tcp|udp)$/
+                upstream_servers << "Upstream Server: #{up_address}:#{up_port} (#{up_port})\n"
               end
             end
 
-            if servers.empty?
-              servers << ['tcp', '8.8.8.8', 53]
-              servers << ['udp', '8.8.8.8', 53]
-            end
-
-            upstream_servers = ''
-            servers.each do |server|
-              upstream_servers << "Upstream Server: #{server[1]}:#{server[2]} (#{server[0]})\n"
-            end
+            Thread.new { EventMachine.next_tick { dns.run(:upstream => servers, :listen => interfaces) } }
 
+            print_info "DNS Server: #{address}:#{port} (#{protocol})"
             print_more upstream_servers
-=end
           end
 
           # Mounts the handler for processing DNS RESTful API requests.

extensions/dns/config.yaml

@@ -13,6 +13,6 @@ beef:
             address: '127.0.0.1'
             port: 5300
             upstream: [
-                ['tcp', '8.8.8.8', 53],
-                ['udp', '8.8.8.8', 53]
+                ['udp', '8.8.8.8', 53],
+                ['tcp', '8.8.8.8', 53]
             ]

extensions/dns/dns.rb

@@ -105,6 +105,26 @@ def remove_ruleset!
           @lock.synchronize { @database.destroy }
         end
 
+        # Starts the DNS server.
+        #
+        # @param options [Hash] server configuration options
+        # @option options [Array<Array>] :upstream upstream DNS servers (if ommitted, unresolvable
+        #   requests return NXDOMAIN)
+        # @option options [Array<Array>] :listen local interfaces to listen on
+        def run(options = {})
+          @lock.synchronize do
+            upstream = options[:upstream]
+            listen = options[:listen]
+
+            unless upstream.nil? || upstream.empty?
+              resolver = RubyDNS::Resolver.new(upstream)
+              @otherwise = Proc.new { |t| t.passthrough!(resolver) }
+            end
+
+            super(:listen => listen)
+          end
+        end
+
         # Entry point for processing incoming DNS requests. Attempts to find a matching rule and
         # sends back its associated response.
         #
@@ -131,12 +151,12 @@ def process(name, resource, transaction)
                 end
               end
 
-              # When no match is found, query upstream servers (if enabled)
               if @otherwise
                 print_debug "No match found, querying upstream servers"
                 @otherwise.call(transaction)
               else
-                print_debug "Failed to handle DNS request for #{name}"
+                print_debug "No match found, sending NXDOMAIN response"
+                transaction.fail!(:NXDomain)
               end
             end
           end