Allow direct set of composition and ensure basic types are used

plugins/providers/docker/config.rb

@@ -29,7 +29,7 @@ module VagrantPlugins
       # file. This can be used for adding networks or volumes.
       #
       # @return [Hash]
-      attr_reader :compose_configuration
+      attr_accessor :compose_configuration
 
       # An optional file name of a Dockerfile to be used when building
       # the image. This requires Docker >1.5.0.
@@ -252,6 +252,11 @@ module VagrantPlugins
         @vagrant_machine = @vagrant_machine.to_sym if @vagrant_machine
 
         @expose.uniq!
+
+        if @compose_configuration.is_a?(Hash)
+          # Ensures configuration is using basic types
+          @compose_configuration = JSON.parse(@compose_configuration.to_json)
+        end
       end
 
       def validate(machine)
@@ -272,6 +277,10 @@ module VagrantPlugins
           end
         end
 
+        if !@compose_configuration.is_a?(Hash)
+          errors << I18n.t("docker_provider.errors.config.compose_configuration_hash")
+        end
+
         if !@create_args.is_a?(Array)
           errors << I18n.t("docker_provider.errors.config.create_args_array")
         end

plugins/providers/docker/driver/compose.rb

@@ -91,7 +91,7 @@ module VagrantPlugins
             update_composition(:apply) do |composition|
               services = composition["services"] ||= {}
               services[name] ||= {}
-              services[name].merge(
+              services[name].merge!(
                 "image" => image,
                 "environment" => env,
                 "expose" => expose,