telegraf/CONTRIBUTING.md

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Plugins

This section is for developers who want to create new collection inputs. 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 inputs.

Plugin Guidelines

• A plugin must conform to the inputs.Input interface.
• Each generated metric automatically has the name of the plugin that generated it prepended. This is to keep plugins honest.
• Plugins should call inputs.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/inputs/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,
        timestamp ...time.Time)
    AddFields(measurement string,
        fields 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 AddFieldsWithTime 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 inputs.Accumulator) error {
    for _, process := range system.Processes() {
        tags := map[string]string {
            "pid": fmt.Sprintf("%d", process.Pid),
        }

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

Plugin Example

package simple

// simple.go

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

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 inputs.Accumulator) error {
    if s.Ok {
        acc.Add("state", "pretty good", nil)
    } else {
        acc.Add("state", "not great", nil)
    }

    return nil
}

func init() {
    inputs.Add("simple", func() inputs.Input { return &Simple{} })
}

Service Plugins

This section is for developers who want to create new "service" collection inputs. A service plugin differs from a regular plugin in that it operates a background service while Telegraf is running. One example would be the statsd plugin, which operates a statsd server.

Service Plugins are substantially more complicated than a regular plugin, as they will require threads and locks to verify data integrity. Service Plugins should be avoided unless there is no way to create their behavior with a regular plugin.

Their interface is quite similar to a regular plugin, with the addition of Start() and Stop() methods.

Service Plugin Guidelines

• Same as the Plugin guidelines, except that they must conform to the inputs.ServiceInput interface.

Service Plugin interface

type ServicePlugin interface {
    SampleConfig() string
    Description() string
    Gather(Accumulator) error
    Start() error
    Stop()
}

Outputs

This section is for developers who want to create a new output sink. Outputs are created in a similar manner as collection plugins, and their interface has similar constructs.

Output Guidelines

• An output must conform to the outputs.Output interface.
• Outputs should call outputs.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/outputs/all/all.go file.
• The SampleConfig function should return valid toml that describes how the output can be configured. This is include in telegraf -sample-config.
• The Description function should say in one line what this output does.

Output interface

type Output interface {
    Connect() error
    Close() error
    Description() string
    SampleConfig() string
    Write(points []*client.Point) error
}

Output Example

package simpleoutput

// simpleoutput.go

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

type Simple struct {
    Ok bool
}

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

func (s *Simple) SampleConfig() string {
    return "url = localhost"
}

func (s *Simple) Connect() error {
    // Make a connection to the URL here
    return nil
}

func (s *Simple) Close() error {
    // Close connection to the URL here
    return nil
}

func (s *Simple) Write(points []*client.Point) error {
    for _, pt := range points {
        // write `pt` to the output sink here
    }
    return nil
}

func init() {
    outputs.Add("simpleoutput", func() outputs.Output { return &Simple{} })
}

Service Outputs

This section is for developers who want to create new "service" output. A service output differs from a regular output in that it operates a background service while Telegraf is running. One example would be the prometheus_client output, which operates an HTTP server.

Their interface is quite similar to a regular output, with the addition of Start() and Stop() methods.

Service Output Guidelines

• Same as the Output guidelines, except that they must conform to the inputs.ServiceOutput interface.

Service Output interface

type ServiceOutput interface {
    Connect() error
    Close() error
    Description() string
    SampleConfig() string
    Write(points []*client.Point) error
    Start() error
    Stop()
}

Unit Tests

Execute short tests

execute make test-short

Execute long tests

As Telegraf collects metrics from several third-party services it becomes a difficult task to mock each service as some of them have complicated protocols which would take some time to replicate.

To overcome this situation we've decided to use docker containers to provide a fast and reproducible environment to test those services which require it. For other situations (i.e: https://github.com/influxdb/telegraf/blob/master/plugins/redis/redis_test.go ) a simple mock will suffice.

To execute Telegraf tests follow these simple steps:

• Install docker following these instructions
• execute make test

OSX users: you will need to install boot2docker or docker-machine. The Makefile will assume that you have a docker-machine box called default to get the IP address.

Unit test troubleshooting

Try cleaning up your test environment by executing make docker-kill and re-running