auto_nat_dns_proxy VirtualBox provider config option [GH-1313]

When set to false, Vagrant will no longer try to automatically manage
NAT DNS proxy settings with VirtualBox.

CHANGELOG.md

@@ -30,6 +30,9 @@ FEATURES:
     This decreases Vagrant's initial startup time considerably.
   - Allow "file://" URLs for box URLs. [GH-1087]
   - Emit "vagrant-mount" upstart event when NFS shares are mounted. [GH-1118]
+  - Add a VirtualBox provider config `auto_nat_dns_proxy` which when set to
+    false will not attempt to automatically manage NAT DNS proxy settings
+    with VirtualBox. [GH-1313]
 
 IMPROVEMENTS / BUG FIXES:
 

plugins/providers/virtualbox/action/sane_defaults.rb

@@ -25,28 +25,12 @@ module VagrantPlugins
           ]
           attempt_and_log(command, "Enabling the Host I/O cache on the SATA controller...")
 
-          enable_dns_proxy = true
-          begin
-            contents = File.read("/etc/resolv.conf")
-
-            if contents =~ /^nameserver 127\.0\.(0|1)\.1$/
-              # The use of both natdnsproxy and natdnshostresolver break on
-              # Ubuntu 12.04 and 12.10 that uses resolvconf with localhost. When used
-              # VirtualBox will give the client dns server 10.0.2.3, while
-              # not binding to that address itself. Therefore disable this
-              # feature if host uses the resolvconf server 127.0.0.1 or
-              # 127.0.1.1
-              @logger.info("Disabling DNS proxy since resolv.conf contains 127.0.0.1 or 127.0.1.1")
-              enable_dns_proxy = false
-            end
-          rescue Errno::ENOENT; end
+          if env[:machine].provider_config.auto_nat_dns_proxy
+            @logger.info("Automatically figuring out whether to enable/disable NAT DNS proxy...")
 
             # Enable/disable the NAT DNS proxy as necessary
-          if enable_dns_proxy
-            command = [
-              "modifyvm", env[:machine].id,
-              "--natdnsproxy1", "on"
-            ]
+            if enable_dns_proxy?
+              command = ["modifyvm", env[:machine].id, "--natdnsproxy1", "on"]
               attempt_and_log(command, "Enable the NAT DNS proxy on adapter 1...")
             else
               command = [ "modifyvm", env[:machine].id, "--natdnsproxy1", "off" ]
@@ -54,6 +38,9 @@ module VagrantPlugins
               command = [ "modifyvm", env[:machine].id, "--natdnshostresolver1", "off" ]
               attempt_and_log(command, "Disable the NAT DNS resolver on adapter 1...")
             end
+          else
+            @logger.info("NOT trying to automatically manage NAT DNS proxy.")
+          end
 
           @app.call(env)
         end
@@ -70,6 +57,30 @@ module VagrantPlugins
           result = @env[:machine].provider.driver.execute_command(command)
           @logger.info("#{log} (exit status = #{result.exit_code})")
         end
+
+        # This uses some heuristics to determine if the NAT DNS proxy should
+        # be enabled or disabled. See the comments within the function body
+        # itself to see the checks it does.
+        #
+        # @return [Boolean]
+        def enable_dns_proxy?
+          begin
+            contents = File.read("/etc/resolv.conf")
+
+            if contents =~ /^nameserver 127\.0\.(0|1)\.1$/
+              # The use of both natdnsproxy and natdnshostresolver break on
+              # Ubuntu 12.04 and 12.10 that uses resolvconf with localhost. When used
+              # VirtualBox will give the client dns server 10.0.2.3, while
+              # not binding to that address itself. Therefore disable this
+              # feature if host uses the resolvconf server 127.0.0.1 or
+              # 127.0.1.1
+              @logger.info("Disabling DNS proxy since resolv.conf contains 127.0.0.1 or 127.0.1.1")
+              return false
+            end
+          rescue Errno::ENOENT; end
+
+          return true
+        end
       end
     end
   end

plugins/providers/virtualbox/config.rb

@@ -1,6 +1,13 @@
 module VagrantPlugins
   module ProviderVirtualBox
     class Config < Vagrant.plugin("2", :config)
+      # Vagrant by default will make "smart" decisions to enable/disable
+      # the NAT DNS proxy. If this is set to `true`, then the DNS proxy
+      # will not be enabled, and it is up to the end user to do it.
+      #
+      # @return [Boolean]
+      attr_accessor :auto_nat_dns_proxy
+
       # An array of customizations to make on the VM prior to booting it.
       #
       # @return [Array]
@@ -17,6 +24,7 @@ module VagrantPlugins
       attr_reader :network_adapters
 
       def initialize
+        @auto_nat_dns_proxy = UNSET_VALUE
         @customizations   = []
         @network_adapters = {}
         @gui              = UNSET_VALUE
@@ -53,6 +61,9 @@ module VagrantPlugins
       # This is the hook that is called to finalize the object before it
       # is put into use.
       def finalize!
+        # Default is to auto the DNS proxy
+        @auto_nat_dns_proxy = true if @auto_nat_dns_proxy == UNSET_VALUE
+
         # Default is to not show a GUI
         @gui = false if @gui == UNSET_VALUE
       end