client: fix panic from 0.8 -> 0.10 upgrade

makeAllocTaskServices did not do a nil check on AllocatedResources
which causes a panic when upgrading directly from 0.8 to 0.10. While
skipping 0.9 is not supported we intend to fix serious crashers caused
by such upgrades to prevent cluster outages.

I did a quick audit of the client package and everywhere else that
accesses AllocatedResources appears to be properly guarded by a nil
check.

client/allocrunner/taskrunner/service_hook.go

@@ -63,7 +63,8 @@ func newServiceHook(c serviceHookConfig) *serviceHook {
 		delay:     c.task.ShutdownDelay,
 	}
 
-	// COMPAT(0.10): Just use the AllocatedResources
+	// COMPAT(0.11): AllocatedResources was added in 0.9 so assume its set
+	//               in 0.11.
 	if c.alloc.AllocatedResources != nil {
 		if res := c.alloc.AllocatedResources.Tasks[c.task.Name]; res != nil {
 			h.networks = res.Networks
@@ -115,7 +116,8 @@ func (h *serviceHook) Update(ctx context.Context, req *interfaces.TaskUpdateRequ
 		canary = req.Alloc.DeploymentStatus.Canary
 	}
 
-	// COMPAT(0.10): Just use the AllocatedResources
+	// COMPAT(0.11): AllocatedResources was added in 0.9 so assume its set
+	//               in 0.11.
 	var networks structs.Networks
 	if req.Alloc.AllocatedResources != nil {
 		if res := req.Alloc.AllocatedResources.Tasks[h.taskName]; res != nil {

client/allocrunner/taskrunner/task_runner.go

@@ -301,7 +301,7 @@ func NewTaskRunner(config *Config) (*TaskRunner, error) {
 		}
 		tr.taskResources = tres
 	} else {
-		// COMPAT(0.10): Upgrade from old resources to new resources
+		// COMPAT(0.11): Upgrade from 0.8 resources to 0.9+ resources
 		// Grab the old task resources
 		oldTr, ok := tr.alloc.TaskResources[tr.taskName]
 		if !ok {

command/agent/consul/client.go

@@ -805,7 +805,9 @@ func (noopRestarter) Restart(context.Context, *structs.TaskEvent, bool) error {
 //
 //TODO(schmichael) rename TaskServices and refactor this into a New method
 func makeAllocTaskServices(alloc *structs.Allocation, tg *structs.TaskGroup) (*TaskServices, error) {
-	if n := len(alloc.AllocatedResources.Shared.Networks); n == 0 {
+	//COMPAT(0.11) AllocatedResources is only nil when upgrading directly
+	//             from 0.8.
+	if alloc.AllocatedResources == nil || len(alloc.AllocatedResources.Shared.Networks) == 0 {
 		return nil, fmt.Errorf("unable to register a group service without a group network")
 	}