From 55634591785c132c416bfe70fc885772ad13ae59 Mon Sep 17 00:00:00 2001
From: Brendan Burns <bburns@google.com>
Date: Tue, 10 Jun 2014 10:00:17 -0700
Subject: [PATCH] Fix the first fit scheduler to randomize.

---
 cmd/apiserver/apiserver.go     |  4 +++-
 pkg/registry/scheduler.go      | 13 ++++++++++---
 pkg/registry/scheduler_test.go | 16 ++++++++++------
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/cmd/apiserver/apiserver.go b/cmd/apiserver/apiserver.go
index a53981ecbd..40ae6cf2df 100644
--- a/cmd/apiserver/apiserver.go
+++ b/cmd/apiserver/apiserver.go
@@ -21,6 +21,7 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"math/rand"
 	"net/http"
 	"time"
 
@@ -74,8 +75,9 @@ func main() {
 		Port:   10250,
 	}
 
+	random := rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
 	storage := map[string]apiserver.RESTStorage{
-		"pods":                  registry.MakePodRegistryStorage(podRegistry, containerInfo, registry.MakeFirstFitScheduler(machineList, podRegistry)),
+		"pods":                  registry.MakePodRegistryStorage(podRegistry, containerInfo, registry.MakeFirstFitScheduler(machineList, podRegistry, random)),
 		"replicationControllers": registry.MakeControllerRegistryStorage(controllerRegistry),
 		"services":               registry.MakeServiceRegistryStorage(serviceRegistry),
 	}
diff --git a/pkg/registry/scheduler.go b/pkg/registry/scheduler.go
index 3ae4cfc86d..377e5d06a0 100644
--- a/pkg/registry/scheduler.go
+++ b/pkg/registry/scheduler.go
@@ -66,12 +66,14 @@ func (s *RoundRobinScheduler) Schedule(pod Pod) (string, error) {
 type FirstFitScheduler struct {
 	machines []string
 	registry PodRegistry
+	random   *rand.Rand
 }
 
-func MakeFirstFitScheduler(machines []string, registry PodRegistry) Scheduler {
+func MakeFirstFitScheduler(machines []string, registry PodRegistry, random *rand.Rand) Scheduler {
 	return &FirstFitScheduler{
 		machines: machines,
 		registry: registry,
+		random: random,
 	}
 }
 
@@ -96,6 +98,7 @@ func (s *FirstFitScheduler) Schedule(pod Pod) (string, error) {
 		host := scheduledPod.CurrentState.Host
 		machineToPods[host] = append(machineToPods[host], scheduledPod)
 	}
+	var machineOptions []string
 	for _, machine := range s.machines {
 		podFits := true
 		for _, scheduledPod := range machineToPods[machine] {
@@ -108,8 +111,12 @@ func (s *FirstFitScheduler) Schedule(pod Pod) (string, error) {
 			}
 		}
 		if podFits {
-			return machine, nil
+			machineOptions = append(machineOptions, machine)
 		}
 	}
-	return "", fmt.Errorf("Failed to find fit for %#v", pod)
+	if len(machineOptions) == 0 {
+		return "", fmt.Errorf("Failed to find fit for %#v", pod)
+	} else {
+		return machineOptions[s.random.Int()%len(machineOptions)], nil
+	}
 }
diff --git a/pkg/registry/scheduler_test.go b/pkg/registry/scheduler_test.go
index 9c30da9909..f94d8b1adf 100644
--- a/pkg/registry/scheduler_test.go
+++ b/pkg/registry/scheduler_test.go
@@ -47,8 +47,9 @@ func TestRandomScheduler(t *testing.T) {
 
 func TestFirstFitSchedulerNothingScheduled(t *testing.T) {
 	mockRegistry := MockPodRegistry{}
-	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry)
-	expectSchedule(scheduler, Pod{}, "m1", t)
+	r := rand.New(rand.NewSource(0))
+	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry, r)
+	expectSchedule(scheduler, Pod{}, "m3", t)
 }
 
 func makePod(host string, hostPorts ...int) Pod {
@@ -78,8 +79,9 @@ func TestFirstFitSchedulerFirstScheduled(t *testing.T) {
 			makePod("m1", 8080),
 		},
 	}
-	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry)
-	expectSchedule(scheduler, makePod("", 8080), "m2", t)
+	r := rand.New(rand.NewSource(0))
+	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry, r)
+	expectSchedule(scheduler, makePod("", 8080), "m3", t)
 }
 
 func TestFirstFitSchedulerFirstScheduledComplicated(t *testing.T) {
@@ -90,7 +92,8 @@ func TestFirstFitSchedulerFirstScheduledComplicated(t *testing.T) {
 			makePod("m3", 80, 443, 8085),
 		},
 	}
-	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry)
+	r := rand.New(rand.NewSource(0))
+	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry, r)
 	expectSchedule(scheduler, makePod("", 8080, 8081), "m3", t)
 }
 
@@ -102,7 +105,8 @@ func TestFirstFitSchedulerFirstScheduledImpossible(t *testing.T) {
 			makePod("m3", 8080),
 		},
 	}
-	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry)
+	r := rand.New(rand.NewSource(0))
+	scheduler := MakeFirstFitScheduler([]string{"m1", "m2", "m3"}, &mockRegistry, r)
 	_, err := scheduler.Schedule(makePod("", 8080, 8081))
 	if err == nil {
 		t.Error("Unexpected non-error.")