Encapsulate time.Since in a defer function

 * Fix how time.Since should be used with defer as described in
   golang/go#60048
 * Previously time.Since(start) is evaluated immediately when the defer
   is defined which means the latency recorded is always 0 seconds. By
   moving the time.Since into a function, it does not get evaluated
   until the function is called which properly times the processing
   latency.

pkg/instancegroups/controller.go

@@ -107,7 +107,9 @@ func (c *Controller) Shutdown() {
 func (c *Controller) sync(key string) error {
 	start := time.Now()
 	klog.V(4).Infof("Instance groups controller: Start processing %s", key)
-	defer klog.V(4).Infof("Instance groups controller: Processing key %s took %v", key, time.Since(start))
+	defer func() {
+		klog.V(4).Infof("Instance groups controller: Processing key %s took %v", key, time.Since(start))
+	}()
 
 	nodeNames, err := utils.GetReadyNodeNames(listers.NewNodeLister(c.lister))
 	if err != nil {