Ensuring that ephemeral disk is present before deciding if we should migrate (#1827)

nomad/structs/structs.go

@@ -3074,7 +3074,17 @@ func (a *Allocation) ShouldMigrate() bool {
 		return false
 	}
 
-	if tg := a.Job.LookupTaskGroup(a.TaskGroup); tg != nil && !tg.EphemeralDisk.Migrate || !tg.EphemeralDisk.Sticky {
+	tg := a.Job.LookupTaskGroup(a.TaskGroup)
+
+	// if the task group is nil or the ephemeral disk block isn't present then
+	// we won't migrate
+	if tg == nil || tg.EphemeralDisk == nil {
+		return false
+	}
+
+	// We won't migrate any data is the user hasn't enabled migration or the
+	// disk is not marked as sticky
+	if !tg.EphemeralDisk.Migrate || !tg.EphemeralDisk.Sticky {
 		return false
 	}
 

nomad/structs/structs_test.go

@@ -1223,6 +1223,21 @@ func TestAllocation_ShouldMigrate(t *testing.T) {
 	if alloc2.ShouldMigrate() {
 		t.Fatalf("bad: %v", alloc)
 	}
+
+	alloc3 := Allocation{
+		TaskGroup: "foo",
+		Job: &Job{
+			TaskGroups: []*TaskGroup{
+				{
+					Name: "foo",
+				},
+			},
+		},
+	}
+
+	if alloc3.ShouldMigrate() {
+		t.Fatalf("bad: %v", alloc)
+	}
 }
 
 func TestTaskArtifact_Validate_Checksum(t *testing.T) {