Dockerfile

FROM scratch
ADD puppetdb-prometheus /
ENTRYPOINT ["/puppetdb-prometheus"]
CMD [""]

main.go

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"strings"
	"time"

	"gopkg.in/yaml.v2"
)

type Node struct {
	Certname  string `json:"certname"`
	Ipaddress string `json:"value"`
}

type Targets struct {
	Targets []string          `yaml:"targets"`
	Labels  map[string]string `yaml:"labels"`
}

const (
	query = "facts { name='ipaddress' and nodes { facts { name='collectd_version' and value ~ '^5\\\\.7' } and resources { type='Class' and title='Collectd' } } }"
	port  = "9103"
	file  = "/etc/prometheus-config/prometheus-targets.yml"
	sleep = 5 * time.Second
)

var labels = map[string]string{
	"job": "puppet",
}

func main() {
	client := &http.Client{}

	for {
		nodes, err := getNodes(client)
		if err != nil {
			fmt.Println(err)
			break
		}

		err = writeNodes(nodes)
		if err != nil {
			fmt.Println(err)
			break
		}

		fmt.Printf("Sleeping for %v\n", sleep)
		time.Sleep(sleep)
	}
}

func getNodes(client *http.Client) (nodes []Node, err error) {
	form := strings.NewReader(fmt.Sprintf("{\"query\":\"%s\"}", query))
	req, err := http.NewRequest("POST", "http://puppetdb:8080/pdb/query/v4", form)
	if err != nil {
		return
	}
	req.Header.Add("Content-Type", "application/json")

	resp, err := client.Do(req)
	if err != nil {
		return
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return
	}

	err = json.Unmarshal(body, &nodes)
	return
}

func writeNodes(nodes []Node) (err error) {
	allTargets := []Targets{}

	for _, node := range nodes {
		targets := Targets{}
		target := fmt.Sprintf("%s:%s", node.Ipaddress, port)
		targets.Targets = append(targets.Targets, target)
		targets.Labels = labels
		targets.Labels["certname"] = node.Certname
		allTargets = append(allTargets, targets)
	}

	d, err := yaml.Marshal(&allTargets)

	err = ioutil.WriteFile(file, d, 0644)
	return nil
}

Makefile

DEPS = $(wildcard */*.go)
VERSION = $(shell git describe --always --dirty)

all: puppetdb-prometheus

puppetdb-prometheus: main.go $(DEPS)
	CGO_ENABLED=0 GOOS=linux \
	  go build -a \
		  -ldflags="-X main.version=$(VERSION)" \
	    -installsuffix cgo -o $@ $<
	strip $@


clean:
	rm -f puppetdb-prometheus

.PHONY: all clean

run.sh

docker run --add-host puppetdb:172.17.0.1 -v $PWD/etc:/etc -d puppetdb_prometheus