detector

Documentation

Overview

Package detector is a tcp server to detect anomalies.

Detector Input protocol

Line based text, for example:

timer.count_ps.get_user 1452674178 3.4

Detection Algorithms

A simple approach to detect anomalies is to set fixed thresholds, but the problem is how large/small they should be. By this way, alertings will be noisily and thresholds are also hard to maintain.

So we explore an automated way.

The well-known 3-sigma rule: http://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule.

States that nearly all values (99.7%) lie within 3 standard deviations of the mean in a normal distribution.

That's to say: If the metric value deviates too much from average, it should be an anomaly!

func IsAnomaly(value float64) bool {
	return math.Abs(value - mean) > 3 * stddev
}

And we name the ratio of the distance to 3 times standard deviation as score:

score = math.Abs(value - mean) / (3.0 * stddev)

If score > 1, that means the metric is currently anomalously trending up.

If score < -1, that means the metric is currently anomalously trending down.

If score is larger than -1 and less than 1, the metric is normal.

Index

• Variables
• type Detector
  • func New(cfg *config.Config, db *storage.DB, flt *filter.Filter) *Detector
  • func (d *Detector) Out(ch chan *models.Metric)
  • func (d *Detector) Start()

Variables

var (
	// ErrProtocol is returned when input line is invalid to parse.
	ErrProtocol = errors.New("detector: invalid protocol input")
	// ErrMetricNameTooLong is returned when input metric name is too long.
	ErrMetricNameTooLong = errors.New("detector: metric name is too long")
	// ErrMetricStampTooSmall is returned when input metric stamp is too small.
	ErrMetricStampTooSmall = errors.New("detector: metric stamp is too small")
)

Types

type Detector

type Detector struct {
	// contains filtered or unexported fields
}

Detector is to detect anomalies.

func New

func New(cfg *config.Config, db *storage.DB, flt *filter.Filter) *Detector

New creates a detector.

func (*Detector) Out

func (d *Detector) Out(ch chan *models.Metric)

Out adds a channel to receive detection results.

func (*Detector) Start

func (d *Detector) Start()

Start the tcp server.