telegraf/CONTRIBUTING.md

Sign the CLA

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Plugins

This section is for developers that want to create new collection plugins. Telegraf is entirely plugin driven. This interface allows for operators to pick and chose what is gathered as well as makes it easy for developers to create new ways of generating metrics.

Plugin authorship is kept as simple as possible to promote people to develop and submit new plugins.

Plugin Guidelines

• A plugin must conform to the plugins.Plugin interface.
• Telegraf promises to run each plugin's Gather function serially. This means developers don't have to worry about thread safety within these functions.
• Each generated metric automatically has the name of the plugin that generated it prepended. This is to keep plugins honest.
• Plugins should call plugins.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/influxdb/telegraf/plugins/all/all.go file.
• The SampleConfig function should return valid toml that describes how the plugin can be configured. This is include in telegraf -sample-config.
• The Description function should say in one line what this plugin does.

Plugin interface

type Plugin interface {
    SampleConfig() string
    Description() string
    Gather(Accumulator) error
}

type Accumulator interface {
    Add(measurement string, value interface{}, tags map[string]string)
    AddValuesWithTime(measurement string,
        values map[string]interface{},
        tags map[string]string,
        timestamp time.Time)
}

Accumulator

The way that a plugin emits metrics is by interacting with the Accumulator.

The Add function takes 3 arguments:

• measurement: A string description of the metric. For instance bytes_read or faults.
• value: A value for the metric. This accepts 5 different types of value:
  • int: The most common type. All int types are accepted but favor using int64 Useful for counters, etc.
  • float: Favor float64, useful for gauges, percentages, etc.
  • bool: true or false, useful to indicate the presence of a state. light_on, etc.
  • string: Typically used to indicate a message, or some kind of freeform information.
  • time.Time: Useful for indicating when a state last occurred, for instance light_on_since.
• tags: This is a map of strings to strings to describe the where or who about the metric. For instance, the net plugin adds a tag named "interface" set to the name of the network interface, like "eth0".

The AddValuesWithTime allows multiple values for a point to be passed. The values used are the same type profile as value above. The timestamp argument allows a point to be registered as having occurred at an arbitrary time.

Let's say you've written a plugin that emits metrics about processes on the current host.

type Process struct {
    CPUTime float64
    MemoryBytes int64
    PID int
}

func Gather(acc plugins.Accumulator) error {
    for _, process := range system.Processes() {
        tags := map[string]string {
            "pid": fmt.Sprintf("%d", process.Pid),
        }

        acc.Add("cpu", process.CPUTime, tags)
        acc.Add("memory", process.MemoryBytes, tags)
    }
}

Example

package simple

// simple.go

import "github.com/influxdb/telegraf/plugins"

type Simple struct {
    Ok bool
}

func (s *Simple) Description() string {
    return "a demo plugin"
}

func (s *Simple) SampleConfig() string {
    return "ok = true # indicate if everything is fine"
}

func (s *Simple) Gather(acc plugins.Accumulator) error {
    if s.Ok {
        acc.Add("state", "pretty good", nil)
    } else {
        acc.Add("state", "not great", nil)
    }

    return nil
}

func init() {
    plugins.Add("simple", func() plugins.Plugin { return &Simple{} })
}

Outputs

TODO: this section will describe requirements for contributing an output