Documentation and making unique first class in the constraint block

jobspec/parse.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"regexp"
+	"strconv"
 	"strings"
 	"time"
 
@@ -256,6 +257,20 @@ func parseConstraints(result *[]*structs.Constraint, obj *hclobj.Object) error {
 			m["RTarget"] = constraint
 		}
 
+		if value, ok := m["unique"]; ok {
+			enabled, err := strconv.ParseBool(value.(string))
+			if err != nil {
+				return err
+			}
+
+			// If it is not enabled, skip the constraint.
+			if !enabled {
+				continue
+			}
+
+			m["Operand"] = "unique"
+		}
+
 		// Build the constraint
 		var c structs.Constraint
 		if err := mapstructure.WeakDecode(m, &c); err != nil {

jobspec/parse_test.go

@@ -192,6 +192,24 @@ func TestParse(t *testing.T) {
 			false,
 		},
 
+		{
+			"unique-constraint.hcl",
+			&structs.Job{
+				ID:       "foo",
+				Name:     "foo",
+				Priority: 50,
+				Region:   "global",
+				Type:     "service",
+				Constraints: []*structs.Constraint{
+					&structs.Constraint{
+						Hard:    true,
+						Operand: "unique",
+					},
+				},
+			},
+			false,
+		},
+
 		{
 			"specify-job.hcl",
 			&structs.Job{

website/source/docs/jobspec/index.html.md

@@ -237,6 +237,14 @@ The `constraint` object supports the following keys:
   the attribute. This sets the operator to "regexp" and the `value`
   to the regular expression.
 
+* `unique` - Unique accepts a boolean value and can be used to mark a Job or
+  a Task Group as requiring placement on unique nodes. If the `unique`
+  constraint is placed on a Job, all of it's Task Groups must be placed on
+  unique nodes. If the `unique` constraint is placed on a Task Group, then
+  multiple instances of that Task Group must be placed on unique nodes. This
+  sets the operator to "unique" if `unique` is set to "true". If set to "false",
+  the constraint is ignored as this is the default behavior.
+
 Below is a table documenting the variables that can be interpreted:
 
 <table class="table table-bordered table-striped">