Rewrite addon-resizer nanny

There will be a single estimator class, providing two ranges: acceptable
and recommended range. As long as current pod requirements and limits fall into
acceptable range, nothing happens. Once either limits or requirements
fall out of acceptable range, they are both updated to lower (when
upscaling) or higher (when downscaling) end of recommended range. This
approach prevents flapping, which took place in previous implementation,
when cluster size oscillated around certain values.

Also, fix the code to actually use poll-period flag.

addon-resizer/Makefile

@@ -25,7 +25,7 @@
 OUT_DIR = build
 PACKAGE = k8s.io/contrib/addon-resizer
 PREFIX = gcr.io/google_containers
-TAG = 1.7
+TAG = 2.0
 
 # Rules for building the real image for deployment to gcr.io
 

addon-resizer/nanny/estimator.go

@@ -18,14 +18,12 @@ package nanny
 
 import (
 	"fmt"
+	"math"
 
 	api "k8s.io/kubernetes/pkg/api/v1"
-
 	"k8s.io/kubernetes/pkg/api/resource"
-)
 
-const (
-	eps = float64(0.01)
+	log "github.com/golang/glog"
 )
 
 // Resource defines the name of a resource, the quantity, and the marginal value.
@@ -34,34 +32,45 @@ type Resource struct {
 	Name               api.ResourceName
 }
 
-// LinearEstimator estimates the amount of resources as r = base + extra*nodes.
-type LinearEstimator struct {
-	Resources []Resource
+// ResourceListPair is a pair of ResourceLists, denoting a range.
+type ResourceListPair struct {
+	lower, upper api.ResourceList
 }
 
-func (e LinearEstimator) scaleWithNodes(numNodes uint64) *api.ResourceRequirements {
-	return calculateResources(numNodes, e.Resources)
+// EstimatorResult is the result of the resource Estimation, used by Estimator struct.
+type EstimatorResult struct {
+	RecommendedRange, AcceptableRange ResourceListPair
 }
 
-// ExponentialEstimator estimates the amount of resources in the way that
-// prevents from frequent updates but may end up with larger resource usage
-// than actually needed (though no more than ScaleFactor).
-type ExponentialEstimator struct {
-	Resources   []Resource
-	ScaleFactor float64
+// Estimator is a struct used for estimating accepted and recommended resource requirements.
+type Estimator struct {
+	Resources            []Resource
+	AcceptanceOffset     int64
+	RecommendationOffset int64
 }
 
-func (e ExponentialEstimator) scaleWithNodes(numNodes uint64) *api.ResourceRequirements {
-	n := uint64(16)
-	for n < numNodes {
-		n = uint64(float64(n)*e.ScaleFactor + eps)
+func decWithPercentageOffset(value uint64, offset int64, rounder func(float64) float64) uint64 {
+	return uint64(int64(value) + int64(rounder(float64(offset)*float64(value)/100)))
+}
+
+func nodesAndOffsetToRange(numNodes uint64, offset int64, res []Resource) ResourceListPair {
+	numNodesMin := decWithPercentageOffset(numNodes, -offset, math.Floor)
+	numNodesMax := decWithPercentageOffset(numNodes, offset, math.Ceil)
+	return ResourceListPair{
+		lower: calculateResources(numNodesMin, res),
+		upper: calculateResources(numNodesMax, res),
 	}
-	return calculateResources(n, e.Resources)
 }
 
-func calculateResources(numNodes uint64, resources []Resource) *api.ResourceRequirements {
-	limits := make(api.ResourceList)
-	requests := make(api.ResourceList)
+func (e Estimator) scaleWithNodes(numNodes uint64) *EstimatorResult {
+	return &EstimatorResult{
+		RecommendedRange: nodesAndOffsetToRange(numNodes, e.RecommendationOffset, e.Resources),
+		AcceptableRange:  nodesAndOffsetToRange(numNodes, e.AcceptanceOffset, e.Resources),
+	}
+}
+
+func calculateResources(numNodes uint64, resources []Resource) api.ResourceList {
+	resourceList := make(api.ResourceList)
 	for _, r := range resources {
 		// Since we want to enable passing values smaller than e.g. 1 millicore per node,
 		// we need to have some more hacky solution here than operating on MilliValues.
@@ -73,11 +82,9 @@ func calculateResources(numNodes uint64, resources []Resource) *api.ResourceRequ
 		newRes := r.Base
 		newRes.Add(overhead)
 
-		limits[r.Name] = newRes
-		requests[r.Name] = newRes
-	}
-	return &api.ResourceRequirements{
-		Limits:   limits,
-		Requests: requests,
+		log.V(4).Infof("New requirement for resource %s with %d nodes is %s", r.Name, numNodes, newRes.String())
+
+		resourceList[r.Name] = newRes
 	}
+	return resourceList
 }