Prioritize deleting the non-running pods when reducing replicas

This changes instructs the replication controller to delete replicas in the
order of "unscheduled (pending)", "scheduled (pending)", and "scheduled
(running)" pods. This is less disruptive than deleting random pods.

pkg/controller/replication_controller_test.go

@@ -18,8 +18,11 @@ package controller
 
 import (
 	"fmt"
+	"math/rand"
 	"net/http"
 	"net/http/httptest"
+	"reflect"
+	"sort"
 	"sync"
 	"testing"
 	"time"
@@ -375,3 +378,52 @@ func TestWatchControllers(t *testing.T) {
 		t.Errorf("Expected 1 call but got 0")
 	}
 }
+
+func TestSortingActivePods(t *testing.T) {
+	numPods := 5
+	podList := newPodList(numPods)
+	pods := make([]*api.Pod, len(podList.Items))
+	for i := range podList.Items {
+		pods[i] = &podList.Items[i]
+	}
+	// pods[0] is not scheduled yet.
+	pods[0].Spec.Host = ""
+	pods[0].Status.Phase = api.PodPending
+	// pods[1] is scheduled but pending.
+	pods[1].Spec.Host = "bar"
+	pods[1].Status.Phase = api.PodPending
+	// pods[2] is unknown.
+	pods[2].Spec.Host = "foo"
+	pods[2].Status.Phase = api.PodUnknown
+	// pods[3] is running but not ready.
+	pods[3].Spec.Host = "foo"
+	pods[3].Status.Phase = api.PodRunning
+	// pods[4] is running and ready.
+	pods[4].Spec.Host = "foo"
+	pods[4].Status.Phase = api.PodRunning
+	pods[4].Status.Conditions = []api.PodCondition{{Type: api.PodReady, Status: api.ConditionTrue}}
+
+	getOrder := func(pods []*api.Pod) []string {
+		names := make([]string, len(pods))
+		for i := range pods {
+			names[i] = pods[i].Name
+		}
+		return names
+	}
+
+	expected := getOrder(pods)
+
+	for i := 0; i < 20; i++ {
+		idx := rand.Perm(numPods)
+		randomizedPods := make([]*api.Pod, numPods)
+		for j := 0; j < numPods; j++ {
+			randomizedPods[j] = pods[idx[j]]
+		}
+		sort.Sort(activePods(randomizedPods))
+		actual := getOrder(randomizedPods)
+
+		if !reflect.DeepEqual(actual, expected) {
+			t.Errorf("expected %v, got %v", expected, actual)
+		}
+	}
+}