telegraf/docs/AGGREGATORS.md

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### 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.
### Aggregator Plugin Example
```go
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) 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()
})
}
```
[telegraf.Aggregator]: https://godoc.org/github.com/influxdata/telegraf#Aggregator
[SampleConfig]: https://github.com/influxdata/telegraf/wiki/SampleConfig