use tickers instead of time.After to avoid memory leak (#5220)

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/route53/route53.go

@@ -84,12 +84,15 @@ func (h *Route53) Run(ctx context.Context) error {
 		return err
 	}
 	go func() {
+		timer := time.NewTimer(h.refresh)
+		defer timer.Stop()
 		for {
+			timer.Reset(h.refresh)
 			select {
 			case <-ctx.Done():
 				log.Debugf("Breaking out of Route53 update loop for %v: %v", h.zoneNames, ctx.Err())
 				return
-			case <-time.After(h.refresh):
+			case <-timer.C:
 				if err := h.updateZones(ctx); err != nil && ctx.Err() == nil /* Don't log error if ctx expired. */ {
 					log.Errorf("Failed to update zones %v: %v", h.zoneNames, err)
 				}