From 25b4939ffa5b979ba7026102fdd80011753945d7 Mon Sep 17 00:00:00 2001
From: Brendan Burns <bburns@google.com>
Date: Tue, 23 Sep 2014 15:38:10 -0700
Subject: [PATCH] Initial cut of a spreading scheduler.

---
 pkg/scheduler/spreading_scheduler.go | 74 ++++++++++++++++++++++++++++
 pkg/scheduler/types.go               | 40 +++++++++++++++
 2 files changed, 114 insertions(+)
 create mode 100644 pkg/scheduler/spreading_scheduler.go
 create mode 100644 pkg/scheduler/types.go

diff --git a/pkg/scheduler/spreading_scheduler.go b/pkg/scheduler/spreading_scheduler.go
new file mode 100644
index 00000000000..e7f992b8f9a
--- /dev/null
+++ b/pkg/scheduler/spreading_scheduler.go
@@ -0,0 +1,74 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package scheduler
+
+import (
+	"fmt"
+	"math/rand"
+	"sort"
+	"sync"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
+)
+
+type SpreadingScheduler struct {
+	pods       PodLister
+	random     *rand.Rand
+	randomLock sync.Mutex
+}
+
+// CalculateSpreadPriority spreads pods by minimizing the number of pods on the same machine with the same labels.
+// Importantly, if there are services in the system that span multiple heterogenous sets of pods, this spreading priority
+// may not provide optimal spreading for the members of that Service.
+// TODO: consider if we want to include Service label sets in the scheduling priority.
+func CalculateSpreadPriority(selector labels.Selector, podLister PodLister, minionLister MinionLister) (HostPriorityList, error) {
+	pods, err := podLister.ListPods(selector)
+	if err != nil {
+		return nil, err
+	}
+	minions, err := minionLister.List()
+	if err != nil {
+		return nil, err
+	}
+
+	counts := map[string]int{}
+	for _, pod := range pods {
+		counts[pod.CurrentState.Host]++
+	}
+
+	result := []HostPriority{}
+	for _, minion := range minions {
+		result = append(result, HostPriority{host: minion, score: counts[minion]})
+	}
+	return result, nil
+}
+
+// Schedule schedules pods to maximize spreading of identical pods across multiple hosts.
+// Does not currently take hostPort scheduling into account.
+// TODO: combine priority based and fit based schedulers into a single scheduler.
+func (s *SpreadingScheduler) Schedule(pod api.Pod, minionLister MinionLister) (string, error) {
+	priorities, err := CalculateSpreadPriority(labels.SelectorFromSet(pod.Labels), s.pods, minionLister)
+	if err != nil {
+		return "", err
+	}
+	sort.Sort(priorities)
+	if len(priorities) == 0 {
+		return "", fmt.Errorf("failed to find a fit: %v", pod)
+	}
+	return priorities[0].host, nil
+}
diff --git a/pkg/scheduler/types.go b/pkg/scheduler/types.go
new file mode 100644
index 00000000000..90d7b642ec8
--- /dev/null
+++ b/pkg/scheduler/types.go
@@ -0,0 +1,40 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package scheduler
+
+// HostPriority represents the priority of scheduling to a particular host, lower priority is better.
+type HostPriority struct {
+	host  string
+	score int
+}
+
+type HostPriorityList []HostPriority
+
+func (h HostPriorityList) Len() int {
+	return len(h)
+}
+
+func (h HostPriorityList) Less(i, j int) bool {
+	if h[i].score == h[j].score {
+		return h[i].host < h[j].host
+	}
+	return h[i].score < h[j].score
+}
+
+func (h HostPriorityList) Swap(i, j int) {
+	h[i], h[j] = h[j], h[i]
+}