providers/docker: warning with host VM about forwarded ports

plugins/providers/docker/action.rb

@@ -27,6 +27,7 @@ module VagrantPlugins
                 end
               end
 
+              b2.use HostMachinePortWarning
               b2.use HostMachinePortChecker
               b2.use HandleForwardedPortCollisions
               b2.use PrepareNFSValidIds
@@ -220,6 +221,7 @@ module VagrantPlugins
       autoload :HasSSH, action_root.join("has_ssh")
       autoload :HostMachine, action_root.join("host_machine")
       autoload :HostMachinePortChecker, action_root.join("host_machine_port_checker")
+      autoload :HostMachinePortWarning, action_root.join("host_machine_port_warning")
       autoload :HostMachineRequired, action_root.join("host_machine_required")
       autoload :HostMachineSyncFolders, action_root.join("host_machine_sync_folders")
       autoload :HostMachineSyncFoldersDisable, action_root.join("host_machine_sync_folders_disable")

plugins/providers/docker/action/host_machine_port_warning.rb

@@ -0,0 +1,37 @@
+module VagrantPlugins
+  module DockerProvider
+    module Action
+      class HostMachinePortWarning
+        def initialize(app, env)
+          @app = app
+        end
+
+        def call(env)
+          if !env[:machine].provider.host_vm?
+            return @app.call(env)
+          end
+
+          # If we have forwarded ports, then notify the user that they
+          # won't be immediately available unless a private network
+          # is created.
+          if has_forwarded_ports?(env[:machine])
+            env[:machine].ui.warn(I18n.t(
+              "docker_provider.host_machine_forwarded_ports"))
+          end
+
+          @app.call(env)
+        end
+
+        protected
+
+        def has_forwarded_ports?(machine)
+          machine.config.vm.networks.each do |type, _|
+            return true if type == :forwarded_port
+          end
+
+          false
+        end
+      end
+    end
+  end
+end

templates/locales/providers_docker.yml

@@ -6,6 +6,12 @@ en:
       Container created: %{id}
     host_machine_disabling_folders: |-
       Removing synced folders...
+    host_machine_forwarded_ports: |-
+      Warning: When using a remote Docker host, forwarded ports will NOT be
+      immediately available on your machine. They will still be forwarded on
+      the remote machine, however, so if you have a way to access the remote
+      machine, then you should be able to access those ports there. This is
+      not an error, it is only an informational message.
     host_machine_needed: |-
       Docker host is required. One will be created if necessary...
     host_machine_ready: |-