Add leader task to api and server side

api/tasks.go

@@ -163,6 +163,7 @@ type Task struct {
 	Vault           *Vault
 	Templates       []*Template
 	DispatchPayload *DispatchPayloadConfig
+	Leader          bool
 }
 
 // TaskArtifact is used to download artifacts before running a task.

jobspec/parse.go

@@ -568,6 +568,7 @@ func parseTasks(jobName string, taskGroupName string, result *[]*structs.Task, l
 			"driver",
 			"env",
 			"kill_timeout",
+			"leader",
 			"logs",
 			"meta",
 			"resources",

jobspec/parse_test.go

@@ -181,6 +181,7 @@ func TestParse(t *testing.T) {
 										Perms:        "777",
 									},
 								},
+								Leader: true,
 							},
 							&structs.Task{
 								Name:   "storagelocker",

jobspec/test-fixtures/basic.hcl

@@ -50,6 +50,7 @@ job "binstore-storagelocker" {
     task "binstore" {
       driver = "docker"
       user   = "bob"
+      leader = true
 
       config {
         image = "hashicorp/binstore"

nomad/structs/diff.go

@@ -403,7 +403,7 @@ func (t *Task) Diff(other *Task, contextual bool) (*TaskDiff, error) {
 		diff.Objects = append(diff.Objects, vDiff)
 	}
 
-	// Artifacts diff
+	// Template diff
 	tmplDiffs := primitiveObjectSetDiff(
 		interfaceSlice(t.Templates),
 		interfaceSlice(other.Templates),

nomad/structs/diff_test.go

@@ -1880,6 +1880,7 @@ func TestTaskDiff(t *testing.T) {
 					"foo": "bar",
 				},
 				KillTimeout: 1 * time.Second,
+				Leader:      true,
 			},
 			New: &Task{
 				Name:   "foo",
@@ -1892,6 +1893,7 @@ func TestTaskDiff(t *testing.T) {
 					"foo": "bar",
 				},
 				KillTimeout: 1 * time.Second,
+				Leader:      true,
 			},
 			Expected: &TaskDiff{
 				Type: DiffTypeNone,
@@ -1911,6 +1913,7 @@ func TestTaskDiff(t *testing.T) {
 					"foo": "bar",
 				},
 				KillTimeout: 1 * time.Second,
+				Leader:      true,
 			},
 			New: &Task{
 				Name:   "foo",
@@ -1923,6 +1926,7 @@ func TestTaskDiff(t *testing.T) {
 					"foo": "baz",
 				},
 				KillTimeout: 2 * time.Second,
+				Leader:      false,
 			},
 			Expected: &TaskDiff{
 				Type: DiffTypeEdited,
@@ -1946,6 +1950,12 @@ func TestTaskDiff(t *testing.T) {
 						Old:  "1000000000",
 						New:  "2000000000",
 					},
+					{
+						Type: DiffTypeEdited,
+						Name: "Leader",
+						Old:  "true",
+						New:  "false",
+					},
 					{
 						Type: DiffTypeEdited,
 						Name: "Meta[foo]",

nomad/structs/structs.go

@@ -1931,8 +1931,9 @@ func (tg *TaskGroup) Validate() error {
 		mErr.Errors = append(mErr.Errors, fmt.Errorf("Task Group %v should have an ephemeral disk object", tg.Name))
 	}
 
-	// Check for duplicate tasks
+	// Check for duplicate tasks and that there is only leader task if any
 	tasks := make(map[string]int)
+	leaderTasks := 0
 	for idx, task := range tg.Tasks {
 		if task.Name == "" {
 			mErr.Errors = append(mErr.Errors, fmt.Errorf("Task %d missing name", idx+1))
@@ -1941,6 +1942,14 @@ func (tg *TaskGroup) Validate() error {
 		} else {
 			tasks[task.Name] = idx
 		}
+
+		if task.Leader {
+			leaderTasks++
+		}
+	}
+
+	if leaderTasks > 1 {
+		mErr.Errors = append(mErr.Errors, fmt.Errorf("Only one task may be marked as leader"))
 	}
 
 	// Validate the tasks
@@ -2289,6 +2298,10 @@ type Task struct {
 	// Artifacts is a list of artifacts to download and extract before running
 	// the task.
 	Artifacts []*TaskArtifact
+
+	// Leader marks the task as the leader within the group. When the leader
+	// task exits, other tasks will be gracefully terminated.
+	Leader bool
 }
 
 func (t *Task) Copy() *Task {

nomad/structs/structs_test.go

@@ -419,8 +419,8 @@ func TestTaskGroup_Validate(t *testing.T) {
 		Name:  "web",
 		Count: 1,
 		Tasks: []*Task{
-			&Task{Name: "web"},
-			&Task{Name: "web"},
+			&Task{Name: "web", Leader: true},
+			&Task{Name: "web", Leader: true},
 			&Task{},
 		},
 		RestartPolicy: &RestartPolicy{
@@ -442,7 +442,10 @@ func TestTaskGroup_Validate(t *testing.T) {
 	if !strings.Contains(mErr.Errors[2].Error(), "Task 3 missing name") {
 		t.Fatalf("err: %s", err)
 	}
-	if !strings.Contains(mErr.Errors[3].Error(), "Task web validation failed") {
+	if !strings.Contains(mErr.Errors[3].Error(), "Only one task may be marked as leader") {
+		t.Fatalf("err: %s", err)
+	}
+	if !strings.Contains(mErr.Errors[4].Error(), "Task web validation failed") {
 		t.Fatalf("err: %s", err)
 	}
 }