74 lines
1.9 KiB
Go
74 lines
1.9 KiB
Go
package cbreaker
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import (
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"fmt"
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"time"
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"github.com/mailgun/timetools"
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log "github.com/sirupsen/logrus"
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)
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// ratioController allows passing portions traffic back to the endpoints,
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// increasing the amount of passed requests using linear function:
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//
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// allowedRequestsRatio = 0.5 * (Now() - Start())/Duration
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//
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type ratioController struct {
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duration time.Duration
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start time.Time
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tm timetools.TimeProvider
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allowed int
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denied int
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log *log.Logger
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}
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func newRatioController(tm timetools.TimeProvider, rampUp time.Duration, log *log.Logger) *ratioController {
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return &ratioController{
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duration: rampUp,
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tm: tm,
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start: tm.UtcNow(),
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log: log,
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}
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}
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func (r *ratioController) String() string {
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return fmt.Sprintf("RatioController(target=%f, current=%f, allowed=%d, denied=%d)", r.targetRatio(), r.computeRatio(r.allowed, r.denied), r.allowed, r.denied)
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}
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func (r *ratioController) allowRequest() bool {
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r.log.Debugf("%v", r)
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t := r.targetRatio()
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// This condition answers the question - would we satisfy the target ratio if we allow this request?
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e := r.computeRatio(r.allowed+1, r.denied)
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if e < t {
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r.allowed++
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r.log.Debugf("%v allowed", r)
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return true
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}
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r.denied++
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r.log.Debugf("%v denied", r)
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return false
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}
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func (r *ratioController) computeRatio(allowed, denied int) float64 {
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if denied+allowed == 0 {
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return 0
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}
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return float64(allowed) / float64(denied+allowed)
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}
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func (r *ratioController) targetRatio() float64 {
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// Here's why it's 0.5:
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// We are watching the following ratio
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// ratio = a / (a + d)
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// We can notice, that once we get to 0.5
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// 0.5 = a / (a + d)
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// we can evaluate that a = d
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// that means equilibrium, where we would allow all the requests
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// after this point to achieve ratio of 1 (that can never be reached unless d is 0)
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// so we stop from there
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multiplier := 0.5 / float64(r.duration)
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return multiplier * float64(r.tm.UtcNow().Sub(r.start))
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}
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