add backoff timer on errors

tls.go

@@ -162,6 +162,7 @@ func (req *TLSRequest) AutoRenew(
 
 	go func() {
 		defer req.done.Done()
+		var backoff int = 5
 
 		for {
 			for i := 0; i < 3; i++ {
@@ -178,7 +179,7 @@ func (req *TLSRequest) AutoRenew(
 				if err != nil {
 
 					// if renew fails then sleep for a while and try again
-					sleep := time.Duration(rgen.Intn(300) + 600)
+					sleep := time.Duration(backoff+rgen.Intn(backoff/4)) * time.Second
 
 					log.WithFields(log.Fields{
 						"attempt": i,
@@ -186,7 +187,10 @@ func (req *TLSRequest) AutoRenew(
 						"error":   err,
 					}).Error("libvault: auto renew failed")
 
-					time.Sleep(sleep * time.Second)
+					time.Sleep(sleep)
+					if backoff < 300 {
+						backoff *= 2
+					}
 
 				} else {
 					// no error