consul: always include task services hook

Previously, Nomad would optimize out the services task runner
hook for tasks which were initially submitted with no services
defined. This causes a problem when the job is later updated to
include service(s) on that task, which will result in nothing
happening because the hook is not present to handle the service
registration in the .Update.

Instead, always enable the services hook. The group services
alloc runner hook is already always enabled.

Fixes #9707

client/allocrunner/taskrunner/task_runner_hooks.go

@@ -101,16 +101,15 @@ func (tr *TaskRunner) initHooks() {
 		}))
 	}
 
-	// If there are any services, add the service hook
-	if len(task.Services) != 0 {
-		tr.runnerHooks = append(tr.runnerHooks, newServiceHook(serviceHookConfig{
-			alloc:     tr.Alloc(),
-			task:      tr.Task(),
-			consul:    tr.consulServiceClient,
-			restarter: tr,
-			logger:    hookLogger,
-		}))
-	}
+	// Always add the service hook. A task with no services on initial registration
+	// may be updated to include services, which must be handled with this hook.
+	tr.runnerHooks = append(tr.runnerHooks, newServiceHook(serviceHookConfig{
+		alloc:     tr.Alloc(),
+		task:      tr.Task(),
+		consul:    tr.consulServiceClient,
+		restarter: tr,
+		logger:    hookLogger,
+	}))
 
 	// If this is a Connect sidecar proxy (or a Connect Native) service,
 	// add the sidsHook for requesting a Service Identity token (if ACLs).