telegraf/docs/AGGREGATORS.md

Aggregator Plugins

This section is for developers who want to create a new aggregator plugin.

Aggregator Plugin Guidelines

• A aggregator must conform to the telegraf.Aggregator interface.
• Aggregators should call aggregators.Add in their init function to register themselves. See below for a quick example.
• To be available within Telegraf itself, plugins must add themselves to the github.com/influxdata/telegraf/plugins/aggregators/all/all.go file.

• The SampleConfig function should return valid toml that describes how the plugin can be configured. This is included in telegraf config. Please consult the SampleConfig page for the latest style guidelines.

• The Description function should say in one line what this aggregator does.
• The Aggregator plugin will need to keep caches of metrics that have passed through it. This should be done using the builtin HashID() function of each metric.
• When the Reset() function is called, all caches should be cleared.

• Follow the recommended CodeStyle.

Aggregator Plugin Example

package min

// min.go

import (
	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/plugins/aggregators"
)

type Min struct {
	// caches for metric fields, names, and tags
	fieldCache map[uint64]map[string]float64
	nameCache  map[uint64]string
	tagCache   map[uint64]map[string]string
}

func NewMin() telegraf.Aggregator {
	m := &Min{}
	m.Reset()
	return m
}

var sampleConfig = `
  ## period is the flush & clear interval of the aggregator.
  period = "30s"
  ## If true drop_original will drop the original metrics and
  ## only send aggregates.
  drop_original = false
`

func (m *Min) Init() error {
	return nil
}

func (m *Min) SampleConfig() string {
	return sampleConfig
}

func (m *Min) Description() string {
	return "Keep the aggregate min of each metric passing through."
}

func (m *Min) Add(in telegraf.Metric) {
	id := in.HashID()
	if _, ok := m.nameCache[id]; !ok {
		// hit an uncached metric, create caches for first time:
		m.nameCache[id] = in.Name()
		m.tagCache[id] = in.Tags()
		m.fieldCache[id] = make(map[string]float64)
		for k, v := range in.Fields() {
			if fv, ok := convert(v); ok {
				m.fieldCache[id][k] = fv
			}
		}
	} else {
		for k, v := range in.Fields() {
			if fv, ok := convert(v); ok {
				if _, ok := m.fieldCache[id][k]; !ok {
					// hit an uncached field of a cached metric
					m.fieldCache[id][k] = fv
					continue
				}
				if fv < m.fieldCache[id][k] {
                    // set new minimum
					m.fieldCache[id][k] = fv
				}
			}
		}
	}
}

func (m *Min) Push(acc telegraf.Accumulator) {
	for id, _ := range m.nameCache {
		fields := map[string]interface{}{}
		for k, v := range m.fieldCache[id] {
			fields[k+"_min"] = v
		}
		acc.AddFields(m.nameCache[id], fields, m.tagCache[id])
	}
}

func (m *Min) Reset() {
	m.fieldCache = make(map[uint64]map[string]float64)
	m.nameCache = make(map[uint64]string)
	m.tagCache = make(map[uint64]map[string]string)
}

func convert(in interface{}) (float64, bool) {
	switch v := in.(type) {
	case float64:
		return v, true
	case int64:
		return float64(v), true
	default:
		return 0, false
	}
}

func init() {
	aggregators.Add("min", func() telegraf.Aggregator {
		return NewMin()
	})
}