works for apply, no tests yet

command/apply.go

@@ -39,6 +39,7 @@ func (c *ApplyCommand) Run(args []string) int {
 		cmdFlags.BoolVar(&destroyForce, "force", false, "force")
 	}
 	cmdFlags.BoolVar(&refresh, "refresh", true, "refresh")
+	cmdFlags.IntVar(&c.Meta.parallelism, "parallelism", 0, "parallelism")
 	cmdFlags.StringVar(&c.Meta.statePath, "state", DefaultStateFilename, "path")
 	cmdFlags.StringVar(&c.Meta.stateOutPath, "state-out", "", "path")
 	cmdFlags.StringVar(&c.Meta.backupPath, "backup", "", "path")
@@ -97,6 +98,7 @@ func (c *ApplyCommand) Run(args []string) int {
 		Destroy:     c.Destroy,
 		Path:        configPath,
 		StatePath:   c.Meta.statePath,
+		Parallelism: c.Meta.parallelism,
 	})
 	if err != nil {
 		c.Ui.Error(err.Error())
@@ -278,6 +280,8 @@ Options:
 
   -no-color              If specified, output won't contain any color.
 
+  -parallelism=#         Limit the number of concurrent operations.
+
   -refresh=true          Update state prior to checking for differences. This
                          has no effect if a plan file is given to apply.
 

command/meta.go

@@ -59,9 +59,13 @@ type Meta struct {
 	//
 	// backupPath is used to backup the state file before writing a modified
 	// version. It defaults to stateOutPath + DefaultBackupExtension
+	//
+	// parallelism is used to control the number of concurrent operations
+	// allowed when walking the graph
 	statePath    string
 	stateOutPath string
 	backupPath   string
+	parallelism  int
 }
 
 // initStatePaths is used to initialize the default values for
@@ -151,6 +155,7 @@ func (m *Meta) Context(copts contextOpts) (*terraform.Context, bool, error) {
 	}
 
 	opts.Module = mod
+	opts.Parallelism = copts.Parallelism
 	opts.State = state.State()
 	ctx := terraform.NewContext(opts)
 	return ctx, false, nil
@@ -430,4 +435,7 @@ type contextOpts struct {
 
 	// Set to true when running a destroy plan/apply.
 	Destroy bool
+
+	// Number of concurrent operations allowed
+	Parallelism int
 }