Try to fix randomness issue.

helpers.go

@@ -11,5 +11,5 @@ var R = rand.New(rand.NewSource(time.Now().UnixNano()))
 // ApplyJitter return a random number
 func ApplyJitter(input int) (output int) {
 	deviation := int(0.25 * float64(input))
-	return input - deviation + rand.Intn(2*deviation)
+	return input - deviation + R.Intn(2*deviation)
 }

helpers_test.go

@@ -9,7 +9,7 @@ func TestApplyJitter(t *testing.T) {
 	R = rand.New(rand.NewSource(0))
 
 	var output = ApplyJitter(100)
-	if output != 106 {
-		t.Errorf("ApplyJitter, expected 10 got %d", output)
+	if output != 99 {
+		t.Errorf("ApplyJitter, expected 99 got %d", output)
 	}
 }

main.go

@@ -67,6 +67,7 @@ var (
 	revision  string
 	buildDate string
 	goVersion = runtime.Version()
+	randomEstafette = rand.New(rand.NewSource(time.Now().UnixNano()))
 )
 
 func init() {
@@ -187,7 +188,10 @@ func getCurrentNodeState(node *apiv1.Node) (state GKEPreemptibleKillerState) {
 // getDesiredNodeState define the state of the node, update node annotations if not present
 func getDesiredNodeState(k KubernetesClient, node *apiv1.Node) (state GKEPreemptibleKillerState, err error) {
 	t := time.Unix(*node.Metadata.CreationTimestamp.Seconds, 0)
-	expiryDatetime := t.Add(24*time.Hour - time.Duration(*drainTimeout)*time.Second - time.Duration(rand.Int63n(24-12))*time.Hour).UTC()
+	drainTimeoutTime := time.Duration(*drainTimeout)*time.Second
+	// 43200 = 12h * 60m * 60s
+	randomTimeBetween0to12 := time.Duration(randomEstafette.Intn((43200)-*drainTimeout))*time.Second
+	expiryDatetime := t.Add(12*time.Hour + drainTimeoutTime + randomTimeBetween0to12).UTC()
 
 	state.ExpiryDatetime = expiryDatetime.Format(time.RFC3339)
 

main_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"math/rand"
 	"testing"
 	"time"
 
@@ -63,20 +64,30 @@ func TestGetCurrentNodeState(t *testing.T) {
 func TestGetDesiredNodeState(t *testing.T) {
 	zerolog.SetGlobalLevel(zerolog.Disabled)
 
-	creationTimestamp := time.Date(2017, 11, 11, 11, 11, 11, 0, time.UTC).Unix()
+	creationTimestamp := time.Date(2017, 11, 11, 12, 00, 00, 0, time.UTC)
+	creationTimestampUnix := creationTimestamp.Unix()
+	creationTimestamp12HoursLater := creationTimestamp.Add(12*time.Hour)
+	creationTimestamp24HoursLater := creationTimestamp.Add(24*time.Hour)
 
 	node := &apiv1.Node{
 		Metadata: &metav1.ObjectMeta{
 			Name:              k8s.String("node-1"),
-			CreationTimestamp: &metav1.Time{Seconds: &creationTimestamp},
+			CreationTimestamp: &metav1.Time{Seconds: &creationTimestampUnix},
 		},
 	}
 
 	client := FakeNewKubernetesClient()
 
 	state, _ := getDesiredNodeState(client, node)
+	stateTS,_ := time.Parse(time.RFC3339,state.ExpiryDatetime)
 
-	if state.ExpiryDatetime != "2017-11-12T04:11:11Z" {
-		t.Errorf("Expect expiry date time to be 2017-11-12T04:11:11Z, instead got %s", state.ExpiryDatetime)
+	if !creationTimestamp12HoursLater.Before(stateTS) && !creationTimestamp24HoursLater.After(stateTS) {
+		t.Errorf("Expect expiry date time to be between 12 and 24h after the creation date %s, instead got %s", creationTimestamp, state.ExpiryDatetime)
+	}
+
+	randomEstafette = rand.New(rand.NewSource(0))
+	stateWithPreseed, _ := getDesiredNodeState(client, node)
+	if stateWithPreseed.ExpiryDatetime != "2017-11-12T11:27:54Z" {
+		t.Errorf("Expect expiry date time to be 2017-11-12T11:27:54Z, instead got %s", stateWithPreseed.ExpiryDatetime)
 	}
 }