Handle leader task being dead in RestoreState

CHANGELOG.md

@@ -32,6 +32,8 @@ BUG FIXES:
    explicitly [GH-3520]
  * cli: Fix passing Consul address via flags [GH-3504]
  * cli: Fix panic when running `keyring` commands [GH-3509]
+ * client: Fix a panic when restoring an allocation with a dead leader task
+   [GH-3502]
  * client: Fix allocation accounting in GC and trigger GCs on allocation
    updates [GH-3445]
  * core: Fixes an issue with jobs that have `auto_revert` set to true, where reverting 

client/alloc_runner.go

@@ -932,6 +932,7 @@ OUTER:
 				r.logger.Printf("[WARN] client: failed to sync alloc %q status upon receiving alloc update: %v",
 					r.allocID, err)
 			}
+
 		case <-r.ctx.Done():
 			taskDestroyEvent = structs.NewTaskEvent(structs.TaskKilled)
 			break OUTER
@@ -967,10 +968,17 @@ func (r *AllocRunner) destroyTaskRunners(destroyEvent *structs.TaskEvent) {
 		tr := r.tasks[leader]
 		r.taskLock.RUnlock()
 
-		r.logger.Printf("[DEBUG] client: alloc %q destroying leader task %q of task group %q first",
-			r.allocID, leader, r.alloc.TaskGroup)
-		tr.Destroy(destroyEvent)
-		<-tr.WaitCh()
+		// Dead tasks don't have a task runner created so guard against
+		// the leader being dead when this AR was saved.
+		if tr == nil {
+			r.logger.Printf("[DEBUG] client: alloc %q leader task %q of task group %q already stopped",
+				r.allocID, leader, r.alloc.TaskGroup)
+		} else {
+			r.logger.Printf("[DEBUG] client: alloc %q destroying leader task %q of task group %q first",
+				r.allocID, leader, r.alloc.TaskGroup)
+			tr.Destroy(destroyEvent)
+			<-tr.WaitCh()
+		}
 	}
 
 	// Then destroy non-leader tasks concurrently

client/alloc_runner_test.go

@@ -1365,6 +1365,97 @@ func TestAllocRunner_TaskLeader_StopTG(t *testing.T) {
 	})
 }
 
+// TestAllocRunner_TaskLeader_StopRestoredTG asserts that when stopping a
+// restored task group with a leader that failed before restoring the leader is
+// not stopped as it does not exist.
+// See https://github.com/hashicorp/nomad/issues/3420#issuecomment-341666932
+func TestAllocRunner_TaskLeader_StopRestoredTG(t *testing.T) {
+	t.Parallel()
+	_, ar := testAllocRunner(false)
+	defer ar.Destroy()
+
+	// Create a leader and follower task in the task group
+	task := ar.alloc.Job.TaskGroups[0].Tasks[0]
+	task.Name = "follower1"
+	task.Driver = "mock_driver"
+	task.KillTimeout = 10 * time.Second
+	task.Config = map[string]interface{}{
+		"run_for": "10s",
+	}
+
+	task2 := ar.alloc.Job.TaskGroups[0].Tasks[0].Copy()
+	task2.Name = "leader"
+	task2.Driver = "mock_driver"
+	task2.Leader = true
+	task2.KillTimeout = 10 * time.Millisecond
+	task2.Config = map[string]interface{}{
+		"run_for": "0s",
+	}
+
+	ar.alloc.Job.TaskGroups[0].Tasks = append(ar.alloc.Job.TaskGroups[0].Tasks, task2)
+	ar.alloc.TaskResources[task2.Name] = task2.Resources
+
+	// Mimic Nomad exiting before the leader stopping is able to stop other tasks.
+	ar.tasks = map[string]*TaskRunner{
+		"leader": NewTaskRunner(ar.logger, ar.config, ar.stateDB, ar.setTaskState,
+			ar.allocDir.NewTaskDir(task2.Name), ar.Alloc(), task2.Copy(),
+			ar.vaultClient, ar.consulClient),
+		"follower1": NewTaskRunner(ar.logger, ar.config, ar.stateDB, ar.setTaskState,
+			ar.allocDir.NewTaskDir(task.Name), ar.Alloc(), task.Copy(),
+			ar.vaultClient, ar.consulClient),
+	}
+	ar.taskStates = map[string]*structs.TaskState{
+		"leader":    {State: structs.TaskStateDead},
+		"follower1": {State: structs.TaskStateRunning},
+	}
+	if err := ar.SaveState(); err != nil {
+		t.Fatalf("error saving state: %v", err)
+	}
+
+	// Create a new AllocRunner to test RestoreState and Run
+	upd2 := &MockAllocStateUpdater{}
+	ar2 := NewAllocRunner(ar.logger, ar.config, ar.stateDB, upd2.Update, ar.alloc,
+		ar.vaultClient, ar.consulClient, ar.prevAlloc)
+	defer ar2.Destroy()
+
+	if err := ar2.RestoreState(); err != nil {
+		t.Fatalf("error restoring state: %v", err)
+	}
+	go ar2.Run()
+
+	// Wait for tasks to be stopped because leader is dead
+	testutil.WaitForResult(func() (bool, error) {
+		_, last := upd2.Last()
+		if last == nil {
+			return false, fmt.Errorf("no updates yet")
+		}
+		if actual := last.TaskStates["leader"].State; actual != structs.TaskStateDead {
+			return false, fmt.Errorf("Task leader is not dead yet (it's %q)", actual)
+		}
+		if actual := last.TaskStates["follower1"].State; actual != structs.TaskStateDead {
+			return false, fmt.Errorf("Task follower1 is not dead yet (it's %q)", actual)
+		}
+		return true, nil
+	}, func(err error) {
+		count, last := upd2.Last()
+		t.Logf("Updates: %d", count)
+		for name, state := range last.TaskStates {
+			t.Logf("%s: %s", name, state.State)
+		}
+		t.Fatalf("err: %v", err)
+	})
+
+	// Make sure it GCs properly
+	ar2.Destroy()
+
+	select {
+	case <-ar2.WaitCh():
+		// exited as expected
+	case <-time.After(10 * time.Second):
+		t.Fatalf("timed out waiting for AR to GC")
+	}
+}
+
 // TestAllocRunner_MoveAllocDir asserts that a file written to an alloc's
 // local/ dir will be moved to a replacement alloc's local/ dir if sticky
 // volumes is on.

client/task_runner.go

@@ -237,7 +237,7 @@ func NewTaskRunner(logger *log.Logger, config *config.Config,
 	// Build the restart tracker.
 	tg := alloc.Job.LookupTaskGroup(alloc.TaskGroup)
 	if tg == nil {
-		logger.Printf("[ERR] client: alloc '%s' for missing task group '%s'", alloc.ID, alloc.TaskGroup)
+		logger.Printf("[ERR] client: alloc %q for missing task group %q", alloc.ID, alloc.TaskGroup)
 		return nil
 	}
 	restartTracker := newRestartTracker(tg.RestartPolicy, alloc.Job.Type)