Add Timestamp Variable

config/interpolate.go

@@ -86,6 +86,13 @@ type UserVariable struct {
 	key string
 }
 
+// A Timestamp variable, used to generate a timestamp. Possibly useful for things
+// like naming and such.
+// "$(timestamp)"
+type TimestampVariable struct {
+	key string
+}
+
 func NewInterpolatedVariable(v string) (InterpolatedVariable, error) {
 	if strings.HasPrefix(v, "count.") {
 		return NewCountVariable(v)
@@ -97,6 +104,8 @@ func NewInterpolatedVariable(v string) (InterpolatedVariable, error) {
 		return NewUserVariable(v)
 	} else if strings.HasPrefix(v, "module.") {
 		return NewModuleVariable(v)
+	} else if strings.HasPrefix(v, "timestamp") {
+		return NewTimestampVariable(v)
 	} else {
 		return NewResourceVariable(v)
 	}
@@ -251,6 +260,16 @@ func (v *UserVariable) GoString() string {
 	return fmt.Sprintf("*%#v", *v)
 }
 
+func NewTimestampVariable(key string) (*TimestampVariable, error) {
+	return &TimestampVariable{
+		key: key,
+	}, nil
+}
+
+func (v *TimestampVariable) FullKey() string {
+	return v.key
+}
+
 // DetectVariables takes an AST root and returns all the interpolated
 // variables that are detected in the AST tree.
 func DetectVariables(root ast.Node) ([]InterpolatedVariable, error) {

terraform/interpolate.go

@@ -6,14 +6,23 @@ import (
 	"os"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/config/lang/ast"
 	"github.com/hashicorp/terraform/config/module"
 )
 
+var InitTime time.Time
+
+// Initial time in UTC, when package was initialized.
+func init() {
+	InitTime = time.Now().UTC()
+}
+
 const (
 	// VarEnvPrefix is the prefix of variables that are read from
 	// the environment to set variables here.
@@ -75,6 +84,8 @@ func (i *Interpolater) Values(
 			err = i.valueSelfVar(scope, n, v, result)
 		case *config.UserVariable:
 			err = i.valueUserVar(scope, n, v, result)
+		case *config.TimestampVariable:
+			err = i.valueTimestampVar(scope, n, v, result)
 		default:
 			err = fmt.Errorf("%s: unknown variable type: %T", n, rawV)
 		}
@@ -198,6 +209,32 @@ func (i *Interpolater) valuePathVar(
 
 }
 
+func (i *Interpolater) valueTimestampVar(
+	scope *InterpolationScope,
+	n string,
+	v *config.TimestampVariable,
+	result map[string]ast.Variable) error {
+	if scope.Resource == nil {
+		return fmt.Errorf("%s: timestamp is only valid within resources", n)
+	}
+
+	if i.Operation == walkValidate {
+		result[n] = ast.Variable{
+			Value: config.UnknownVariableValue,
+			Type:  ast.TypeString,
+		}
+		return nil
+	}
+
+	value := strconv.FormatInt(InitTime.Unix(), 10)
+
+	result[n] = ast.Variable{
+		Value: value,
+		Type:  ast.TypeString,
+	}
+	return nil
+}
+
 func (i *Interpolater) valueResourceVar(
 	scope *InterpolationScope,
 	n string,