The Beater Interface

The New() function receives the configuration options defined for the Beat and creates a Beat object based on them. Here’s the New() function that’s generated in beater/countbeat.go when you run the Beat generator:

func New(b *beat.Beat, cfg *common.Config) (beat.Beater, error) {
	config := config.DefaultConfig
	if err := cfg.Unpack(&config); err != nil {
		return nil, fmt.Errorf("Error reading config file: %v", err)
	}

	bt := &Countbeat{
		done:   make(chan struct{}),
		config: config,
	}
	return bt, nil
}

Pointers are used to distinguish between when the setting is completely missing from the configuration file and when it has a value that matches the type’s default value.

The recommended way of handling the configuration (as shown in the code example) is to create a Config structure with the configuration options and a DefaultConfig with the default configuration options.

When you use the Beat generator, the Go structures for a basic config are added to config/config.go:

package config

import "time"

type Config struct {
	Period time.Duration `config:"period"`
}

var DefaultConfig = Config{
	Period: 1 * time.Second,
}

This mirrors the config options that are defined in the config file, countbeat.yml.

countbeat:
  # Defines how often an event is sent to the output
  period: 10s

The config file is generated when you run make setup to set up the beat. The file contains basic configuration information. To add configuration options to your Beat, you need to update the Go structures in config/config.go and add the corresponding config options to _meta/beat.yml.

For example, if you add a config option called path to the Go structures:

type Config struct {
    Period time.Duration `config:"period"`
    Path   string        `config:"path"`
}

var DefaultConfig = Config{
    Period: 1 * time.Second,
    Path:   ".",
}

You also need to add path to _meta/beat.yml:

countbeat:
  period: 10s
  path: "."

After modifying beat.yml, run the following command to apply your updates:

make update

The Run method contains your main application loop.

func (bt *Countbeat) Run(b *beat.Beat) error {
	logp.Info("countbeat is running! Hit CTRL-C to stop it.")

	bt.client = b.Publisher.Connect()
	ticker := time.NewTicker(bt.config.Period)
	counter := 1
	for {
		select {
		case <-bt.done:
			return nil
		case <-ticker.C:
		}

		event := common.MapStr{ 
			"@timestamp": common.Time(time.Now()), 
			"type":       b.Name,
			"counter":    counter,
		}
		bt.client.PublishEvent(event) 
		logp.Info("Event sent")
		counter++
	}
}

Inside the loop, the Beat sleeps for a configurable period of time and then captures the required data and sends it to the publisher. The publisher client is available as part of the Beat object through the client variable.

The event := common.MapStr{} stores the event in a json format, and bt.client.PublishEvent(event) publishes data to Elasticsearch. In the generated Beat, there are three fields in the event: @timestamp, type, and counter.

When you add fields to the event object, you also need to add them to the _meta/fields.yml file:

- key: countbeat
  title: countbeat
  description:
  fields:
    - name: counter
      type: long
      required: true
      description: >
        PLEASE UPDATE DOCUMENTATION

Remember to run make update to apply your updates.

For more information on defining field mappings in _meta/fields.yml, see Defining field mappings.

For more detail about naming the fields in an event, see Naming Conventions.

The Stop method is called when the Beat is signaled to stop, for example through the SIGTERM signal on Unix systems or the service control interface on Windows. This method simply closes the channel which breaks the main loop.

func (bt *Countbeat) Stop() {
	bt.client.Close()
	close(bt.done)
}

If you follow the Countbeat model and put your Beat-specific code in its own type that implements the Beater interface, the code from your main package is very simple:

package main

import (
	"os"

	"github.com/elastic/beats/libbeat/beat"
	"github.com/elastic/beats/libbeat/cmd"
	"github.com/elastic/beats/libbeat/cmd/instance"

	"github.com/kimjmin/countbeat/beater"
)

var RootCmd = cmd.GenRootCmdWithSettings(beater.New, instance.Settings{Name: "countbeat"})

func main() {
	if err := RootCmd.Execute(); err != nil {
		os.Exit(1)
	}
}