diff --git a/pkg/loadtester/task_ngrinder.go b/pkg/loadtester/task_ngrinder.go
index 998fe73a..f090f971 100644
--- a/pkg/loadtester/task_ngrinder.go
+++ b/pkg/loadtester/task_ngrinder.go
@@ -22,6 +22,7 @@ func init() {
 		clone := metadata["clone"]
 		username := metadata["username"]
 		passwd := metadata["passwd"]
+		pollInterval := metadata["pollInterval"]
 		if server == "" || clone == "" || username == "" || passwd == "" {
 			return nil, errors.New("server, clone, username and passwd are required metadata")
 		}
@@ -38,27 +39,38 @@ func init() {
 		if err != nil {
 			return nil, errors.New("metadata auth provided is invalid, base64 encoded username:password required")
 		}
+		interval, err := strconv.Atoi(pollInterval)
+		if err != nil {
+			interval = 1
+		}
+
 		return &NGrinderTask{
 			TaskBase{canary, logger},
-			baseUrl, cloneId, username, string(passwdDecoded), -1, 5,
+			baseUrl, cloneId, username, string(passwdDecoded), -1, time.Duration(interval),
 		}, nil
 	})
 }
 
 type NGrinderTask struct {
 	TaskBase
-	baseUrl      *url.URL
-	cloneId      int
-	username     string
-	passwd       string
-	testId       int
+	// base url of ngrinder server, e.g. http://ngrinder:8080
+	baseUrl *url.URL
+	// template test to clone from
+	cloneId int
+	// http basic auth
+	username string
+	passwd   string
+	// current ngrinder test id
+	testId int
+	// task status polling interval
 	pollInterval time.Duration
 }
 
 func (task *NGrinderTask) Hash() string {
-	return hash(task.canary + task.CloneAndStartEndpoint().String())
+	return hash(task.canary + string(task.cloneId))
 }
 
+// nGrinder REST endpoints
 func (task *NGrinderTask) CloneAndStartEndpoint() *url.URL {
 	path, _ := url.Parse(fmt.Sprintf("perftest/api/%d/clone_and_start", task.cloneId))
 	return task.baseUrl.ResolveReference(path)
@@ -72,6 +84,7 @@ func (task *NGrinderTask) StopEndpoint() *url.URL {
 	return task.baseUrl.ResolveReference(path)
 }
 
+// initiate a clone_and_start request and get new test id from response
 func (task *NGrinderTask) Run(ctx context.Context) bool {
 	url := task.CloneAndStartEndpoint().String()
 	result, err := task.request("POST", url, ctx)
@@ -88,6 +101,7 @@ func (task *NGrinderTask) String() string {
 	return task.canary + task.CloneAndStartEndpoint().String()
 }
 
+// polling execution status of the new test and check if finished
 func (task *NGrinderTask) PollStatus(ctx context.Context) bool {
 	// wait until ngrinder test finished/canceled or timedout
 	tickChan := time.NewTicker(time.Second * task.pollInterval).C
@@ -116,15 +130,20 @@ func (task *NGrinderTask) PollStatus(ctx context.Context) bool {
 	}
 }
 
+// send request, handle error, and eavl response json
 func (task *NGrinderTask) request(method, url string, ctx context.Context) (map[string]interface{}, error) {
+	task.logger.Debugf("send %s request to %s", method, url)
 	req, _ := http.NewRequest(method, url, nil)
 	req.SetBasicAuth(task.username, task.passwd)
 	if ctx != nil {
 		req = req.WithContext(ctx)
 	}
 	resp, err := http.DefaultClient.Do(req)
-	defer resp.Body.Close()
+	if resp != nil {
+		defer resp.Body.Close()
+	}
 	if err != nil {
+		task.logger.Errorf("bad request: %s", err.Error())
 		return nil, err
 	}
 	respBytes, err := ioutil.ReadAll(resp.Body)