/
balance_breaker.go
622 lines (545 loc) · 16.1 KB
/
balance_breaker.go
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package balancing
import (
"fmt"
"math"
"net/http"
"sort"
"sync"
"time"
"github.com/allegro/akubra/internal/akubra/log"
"github.com/allegro/akubra/internal/akubra/metrics"
"github.com/allegro/akubra/internal/akubra/storages/backend"
"github.com/allegro/akubra/internal/akubra/storages/config"
)
// ResponseTimeBalancer proxies calls to balancing nodes
type ResponseTimeBalancer struct {
Nodes []Node
}
// Elect elects node and calls it with args
func (balancer *ResponseTimeBalancer) Elect(skipNodes ...Node) (Node, error) {
start := time.Now()
var elected Node
for _, node := range balancer.Nodes {
if !node.IsActive() || inSkipNodes(skipNodes, node) {
continue
}
if elected == nil {
elected = node
continue
}
if nodeWeight(node) < nodeWeight(elected) {
elected = node
}
}
if elected == nil {
return nil, ErrNoActiveNodes
}
// Disrupt node stats. If all nodes has zero weight only first would
// get all the load unless response will come
elected.UpdateTimeSpent(time.Since(start))
return elected, nil
}
func inSkipNodes(skipNodes []Node, node Node) bool {
for _, skipNode := range skipNodes {
if node == skipNode {
return true
}
}
return false
}
// Node is interface of call node
type Node interface {
Calls() float64
TimeSpent() float64
IsActive() bool
SetActive(bool)
UpdateTimeSpent(time.Duration)
}
func nodeWeight(node Node) float64 {
return node.TimeSpent()
}
var (
// ErrNoActiveNodes is issued if all nodes are inactive
ErrNoActiveNodes = fmt.Errorf("Balancer has no nodes to call")
)
func NewCallMeter(retention, resolution time.Duration) *CallMeter {
return &CallMeter{
retention: retention,
resolution: resolution,
histogram: newTimeHistogram(retention, resolution, time.Now),
now: time.Now,
}
}
func newCallMeterWithTimer(retention, resolution time.Duration, now func() time.Time) *CallMeter {
cm := NewCallMeter(retention, resolution)
cm.now = now
cm.histogram = newTimeHistogram(retention, resolution, now)
cm.histogram.now = now
return cm
}
// CallMeter implements Node interface
type CallMeter struct {
retention time.Duration
resolution time.Duration
now func() time.Time
histogram *histogram
inActiveSince time.Time
statsShiftMx sync.Mutex
}
// UpdateTimeSpent aggregates data about call duration
func (meter *CallMeter) UpdateTimeSpent(duration time.Duration) {
series := meter.histogram.pickSeries(meter.now())
if series == nil {
return
}
series.Add(float64(duration), meter.now())
}
// Calls returns number of calls in last bucket
func (meter *CallMeter) Calls() float64 {
return meter.CallsInLastPeriod(meter.resolution)
}
// CallsInLastPeriod returns number of calls in last duration
func (meter *CallMeter) CallsInLastPeriod(period time.Duration) float64 {
lastPeriodSeries := meter.histogram.PickLastSeries(period)
sum := float64(0)
now := meter.now()
for _, series := range lastPeriodSeries {
values := series.ValueRange(now.Add(-period), now)
sum += float64(len(values))
}
return sum
}
// IsActive aseses if node should be active
func (meter *CallMeter) IsActive() bool {
return meter.inActiveSince == time.Time{}
}
// SetActive sets meter state
func (meter *CallMeter) SetActive(active bool) {
if meter.IsActive() && !active {
meter.inActiveSince = meter.now()
}
if !meter.IsActive() && active {
meter.histogram.shiftData(meter.now().Sub(meter.inActiveSince))
meter.inActiveSince = time.Time{}
}
}
// TimeSpent returns float64 repesentation of time spent in execution
func (meter *CallMeter) TimeSpent() float64 {
allSeries := meter.histogram.PickLastSeries(meter.resolution)
sum := float64(0)
now := meter.now()
for _, series := range allSeries {
series.ValueRangeFun(now.Add(-meter.resolution), now, func(value *timeValue) {
sum += value.value
})
}
return sum
}
type dataSeries struct {
data []*timeValue
mx sync.Mutex
}
func (series *dataSeries) Add(value float64, dateTime time.Time) {
series.mx.Lock()
defer series.mx.Unlock()
series.data = append(series.data, &timeValue{dateTime, value})
}
func (series *dataSeries) ValueRangeFun(timeStart, timeEnd time.Time, fun func(*timeValue)) {
for _, timeVal := range series.data {
if (timeStart == timeVal.date || timeStart.Before(timeVal.date)) && timeEnd.After(timeVal.date) {
fun(timeVal)
}
}
}
func (series *dataSeries) ValueRange(timeStart, timeEnd time.Time) []float64 {
dataRange := []float64{}
series.ValueRangeFun(timeStart, timeEnd, func(value *timeValue) {
dataRange = append(dataRange, value.value)
})
return dataRange
}
type timeValue struct {
date time.Time
value float64
}
func newTimeHistogram(retention, resolution time.Duration, now func() time.Time) *histogram {
return &histogram{
t0: now(),
resolution: resolution,
retention: retention,
now: now,
mx: sync.Mutex{},
}
}
type histogram struct {
t0 time.Time
retention time.Duration
resolution time.Duration
data []*dataSeries
now func() time.Time
mx sync.Mutex
}
// PickLastSeries returns slice of dataSeries tracking at least given period of time
func (h *histogram) PickLastSeries(period time.Duration) []*dataSeries {
h.mx.Lock()
defer h.mx.Unlock()
if period > h.retention {
period = h.retention
}
h.unshiftData(h.now())
cellsNumber := math.Ceil(float64(period)/float64(h.resolution)) + 1
now := h.now()
stop := h.index(now) + 1
start := int(math.Max(float64(stop-int(cellsNumber)), 0))
if start > len(h.data) || stop > len(h.data) {
return []*dataSeries{}
}
return h.data[start:stop]
}
func (h *histogram) pickSeries(at time.Time) *dataSeries {
h.mx.Lock()
defer h.mx.Unlock()
idx := h.index(at)
log.Debugf("pickSeries idx %d, cells %d, datalen %d", idx, h.cellsCount(), len(h.data))
if idx < 0 {
return nil
}
if idx >= h.cellsCount() || idx >= len(h.data) {
h.unshiftData(at)
idx = h.index(at)
log.Debugf("pickSeries unshifted idx %d, cells %d, datalen %d", idx, h.cellsCount(), len(h.data))
}
return h.data[idx]
}
func (h *histogram) index(now time.Time) int {
sinceStart := float64(now.Sub(h.t0))
idx := math.Floor(sinceStart / float64(h.resolution))
return int(idx)
}
func (h *histogram) cellsCount() int {
return int(math.Ceil(float64(h.retention)/float64(h.resolution))) + 1
}
func (h *histogram) growSeries() {
for len(h.data) < h.cellsCount() {
h.data = append(h.data, &dataSeries{mx: sync.Mutex{}})
}
}
func (h *histogram) unshiftData(now time.Time) {
idx := h.index(now)
shiftSize := idx - len(h.data) + 1
if shiftSize > 0 && shiftSize < len(h.data) {
h.t0 = h.t0.Add(time.Duration(shiftSize) * h.resolution)
h.data = h.data[shiftSize:]
}
if shiftSize > 0 && len(h.data) > 0 && shiftSize >= len(h.data) {
h.t0 = now
h.data = []*dataSeries{}
}
h.growSeries()
}
func (h *histogram) shiftData(delta time.Duration) {
newT0 := h.t0.Add(delta)
if newT0.After(h.now()) {
return
}
h.t0 = newT0
for _, series := range h.data {
for _, value := range series.data {
value.date = value.date.Add(delta)
}
}
}
// Breaker is interface of citcuit breaker
type Breaker interface {
Record(duration time.Duration, success bool) bool
ShouldOpen() bool
}
func NewBreaker(retention int, callTimeLimit time.Duration,
timeLimitPercentile, errorRate float64,
closeDelay, maxDelay time.Duration) Breaker {
return &NodeBreaker{
timeData: newLenLimitCounter(retention),
failures: newLenLimitCounter(retention),
rate: errorRate,
callTimeLimit: callTimeLimit,
timeLimitPercentile: timeLimitPercentile,
now: time.Now,
closeDelay: closeDelay,
maxDelay: maxDelay,
}
}
// NodeBreaker is implementation of Breaker interface
type NodeBreaker struct {
rate float64
callTimeLimit time.Duration
timeLimitPercentile float64
timeData *lengthDelimitedCounter
failures *lengthDelimitedCounter
now func() time.Time
closeDelay time.Duration
maxDelay time.Duration
state *openStateTracker
}
// Record collects call data and returns bool if breaker should be opened
func (breaker *NodeBreaker) Record(duration time.Duration, success bool) bool {
breaker.timeData.Add(float64(duration))
failValue := float64(1)
if success {
failValue = float64(0)
}
breaker.failures.Add(failValue)
return breaker.ShouldOpen()
}
// ShouldOpen checks if breaker should be opened
func (breaker *NodeBreaker) ShouldOpen() bool {
exceeded := breaker.limitsExceeded()
if breaker.state != nil {
return breaker.isHalfOpen(exceeded)
}
if exceeded {
breaker.openBreaker()
}
return exceeded
}
func (breaker *NodeBreaker) isHalfOpen(exceeded bool) bool {
state, changed := breaker.state.currentState(breaker.now(), exceeded)
if state == closed {
if changed {
breaker.state = nil
}
return false
}
if state == halfopen {
if changed {
breaker.reset()
}
return false
}
return true
}
func (breaker *NodeBreaker) limitsExceeded() bool {
errorRate := breaker.errorRate()
if errorRate > breaker.rate {
breaker.openBreaker()
log.Debugf("Breaker: error rate exceeded %f", errorRate)
return true
}
percentile := breaker.timeData.Percentile(breaker.timeLimitPercentile)
if percentile > float64(breaker.callTimeLimit) {
breaker.openBreaker()
log.Debugf("Breaker: time percentile exceeded %f / %f", percentile, float64(breaker.callTimeLimit))
return true
}
return false
}
func (breaker *NodeBreaker) openBreaker() {
if breaker.state != nil {
return
}
breaker.state = newOpenStateTracker(
breaker.now(), breaker.closeDelay, breaker.maxDelay)
}
func (breaker *NodeBreaker) reset() {
breaker.timeData.Reset()
breaker.failures.Reset()
}
func (breaker *NodeBreaker) errorRate() float64 {
sum := breaker.failures.Sum()
count := float64(len(breaker.failures.values))
return sum / count
}
func newLenLimitCounter(retention int) *lengthDelimitedCounter {
return &lengthDelimitedCounter{
values: make([]float64, retention),
}
}
type lengthDelimitedCounter struct {
values []float64
nextIdx int
mx sync.Mutex
}
// Add acumates new values
func (counter *lengthDelimitedCounter) Add(value float64) {
counter.mx.Lock()
defer counter.mx.Unlock()
index := counter.nextIdx
counter.values[index] = value
counter.nextIdx = (counter.nextIdx + 1) % cap(counter.values)
}
// Sum returns sum of values
func (counter *lengthDelimitedCounter) Sum() float64 {
sum := float64(0)
for _, v := range counter.values {
sum += v
}
return sum
}
// Percentile return value for given percentile
func (counter *lengthDelimitedCounter) Percentile(percentile float64) float64 {
snapshot := make([]float64, len(counter.values))
copy(snapshot, counter.values)
sort.Float64s(snapshot)
pertcentileIndex := int(math.Floor(float64(len(snapshot)) * percentile))
return snapshot[pertcentileIndex]
}
func (counter *lengthDelimitedCounter) Reset() {
for idx := range counter.values {
counter.values[idx] = 0
}
}
type breakerState int
const (
open breakerState = 0
halfopen = iota
closed = iota
)
func newOpenStateTracker(start time.Time, changeDelay, maxDelay time.Duration) *openStateTracker {
return &openStateTracker{
lastChange: start,
state: open,
changeDelay: changeDelay,
maxDelay: maxDelay,
}
}
type openStateTracker struct {
state breakerState
lastChange time.Time
changeDelay time.Duration
maxDelay time.Duration
closeIteration float64
}
func (tracker *openStateTracker) currentDelay() time.Duration {
multiplier := int(math.Pow(2, tracker.closeIteration))
delayDuration := tracker.changeDelay * time.Duration(multiplier)
if delayDuration < tracker.maxDelay {
return delayDuration
}
return tracker.maxDelay
}
func (tracker *openStateTracker) currentState(now time.Time, limitsExceeded bool) (breakerState, bool) {
if limitsExceeded && tracker.state != open {
tracker.state = open
tracker.lastChange = now
tracker.closeIteration++
return tracker.state, true
}
changed := false
if now.Sub(tracker.lastChange) < tracker.currentDelay() {
return tracker.state, changed
}
changed = true
tracker.lastChange = now
if tracker.state == open {
tracker.state = halfopen
return halfopen, changed
}
if tracker.state == halfopen {
if limitsExceeded {
tracker.state = open
tracker.closeIteration++
} else {
tracker.state = closed
}
}
return tracker.state, changed
}
// MeasuredStorage coordinates metrics collection
type MeasuredStorage struct {
Node
Breaker
http.RoundTripper
Name string
}
// RoundTrip implements http.RoundTripper
func (ms *MeasuredStorage) RoundTrip(req *http.Request) (*http.Response, error) {
start := time.Now()
reqID, _ := req.Context().Value(log.ContextreqIDKey).(string)
log.Debugf("MeasuredStorage %s: Got request id %s\n", ms.Name, reqID)
resp, err := ms.RoundTripper.RoundTrip(req)
duration := time.Since(start)
success := backendSuccess(resp, err)
open := ms.Breaker.Record(duration, success)
log.Debugf("MeasuredStorage %s: Request %s took %s was successful: %t, opened breaker %t\n", ms.Name, reqID, duration, success, open)
ms.Node.UpdateTimeSpent(duration)
ms.Node.SetActive(!open)
reportMetrics(ms.RoundTripper, start, open)
return resp, err
}
func backendSuccess(response *http.Response, err error) bool {
return err == nil && response != nil && response.StatusCode < 500
}
// IsActive checks Breaker status propagates it to Node compound
func (ms *MeasuredStorage) IsActive() bool {
isActive := !ms.Breaker.ShouldOpen()
ms.Node.SetActive(isActive)
return ms.Node.IsActive()
}
func reportMetrics(rt http.RoundTripper, since time.Time, open bool) {
if b, ok := rt.(*backend.Backend); ok {
prefix := fmt.Sprintf("reqs.backend.%s.balancer", b.Name)
metrics.UpdateSince(prefix+".duration", since)
if open {
metrics.UpdateGauge(prefix+".open", 1)
} else {
metrics.UpdateGauge(prefix+".open", 0)
}
}
}
// NewBalancerPrioritySet configures prioritized balancers stack
func NewBalancerPrioritySet(storagesConfig config.Storages, backends map[string]http.RoundTripper) *BalancerPrioritySet {
priorities := make([]int, 0)
priotitiesFilter := make(map[int]struct{})
priorityStorage := make(map[int][]*MeasuredStorage)
for _, storageConfig := range storagesConfig {
breaker := NewBreaker(storageConfig.BreakerProbeSize,
storageConfig.BreakerCallTimeLimit.Duration,
storageConfig.BreakerCallTimeLimitPercentile,
storageConfig.BreakerErrorRate,
storageConfig.BreakerBasicCutOutDuration.Duration,
storageConfig.BreakerMaxCutOutDuration.Duration,
)
meter := NewCallMeter(storageConfig.MeterRetention.Duration, storageConfig.MeterResolution.Duration)
backend, ok := backends[storageConfig.Name]
if !ok {
log.Fatalf("No defined storage %s\n", storageConfig.Name)
}
if _, ok := priotitiesFilter[storageConfig.Priority]; !ok {
priorities = append(priorities, storageConfig.Priority)
priotitiesFilter[storageConfig.Priority] = struct{}{}
}
mstorage := &MeasuredStorage{Breaker: breaker, Node: Node(meter), RoundTripper: backend, Name: storageConfig.Name}
if _, ok := priorityStorage[storageConfig.Priority]; !ok {
priorityStorage[storageConfig.Priority] = make([]*MeasuredStorage, 0, 1)
}
priorityStorage[storageConfig.Priority] = append(
priorityStorage[storageConfig.Priority], mstorage)
}
sort.Ints(priorities)
bps := &BalancerPrioritySet{balancers: []*ResponseTimeBalancer{}}
for _, key := range priorities {
nodes := make([]Node, 0)
for _, node := range priorityStorage[key] {
nodes = append(nodes, Node(node))
}
balancer := &ResponseTimeBalancer{Nodes: nodes}
bps.balancers = append(bps.balancers, balancer)
}
return bps
}
// BalancerPrioritySet selects storage by priority and availability
type BalancerPrioritySet struct {
balancers []*ResponseTimeBalancer
}
// GetMostAvailable returns balancer member
func (bps *BalancerPrioritySet) GetMostAvailable(skipNodes ...Node) *MeasuredStorage {
for level, balancer := range bps.balancers {
node, err := balancer.Elect(skipNodes...)
if err == ErrNoActiveNodes {
log.Printf("Changed prioryty level to %d", level)
continue
}
ms := node.(*MeasuredStorage)
return ms
}
return nil
}