Add metric 'rabbitmq_up'

The new metric exposes whether the last scrape of RabbitMQ was
successful. It is inspired by the haproxy_exporter which exposes the
metric `haproxy_up`.
The value of `rabbitmq_up` is either `1` or `0`. It can be used to
determine whether the RabbitMQ process being scraped is up-and-running.

In order to be able to set the metric, some functions have been
rewritten to return error values instead of using callbacks.

exporter.go

@@ -12,19 +12,27 @@ type exporter struct {
 	queueMetricsGauge   map[string]*prometheus.GaugeVec
 	queueMetricsCounter map[string]*prometheus.CounterVec
 	overviewMetrics     map[string]prometheus.Gauge
+	upMetric            prometheus.Gauge
 }
 
 func newExporter() *exporter {
 	return &exporter{
 		queueMetricsGauge:   queueGaugeVec,
 		queueMetricsCounter: queueCounterVec,
 		overviewMetrics:     overviewMetricDescription,
+		upMetric:            upMetricDescription,
 	}
 }
 
 func (e *exporter) fetchRabbit() {
-	rabbitMqOverviewData := getOverviewMap(config)
-	rabbitMqQueueData := getQueueInfo(config)
+	rabbitMqOverviewData, overviewError := getOverviewMap(config)
+	rabbitMqQueueData, queueError := getQueueInfo(config)
+
+	if overviewError != nil || queueError != nil {
+		e.upMetric.Set(0)
+	} else {
+		e.upMetric.Set(1)
+	}
 
 	log.WithField("overviewData", rabbitMqOverviewData).Debug("Overview data")
 	for key, gauge := range e.overviewMetrics {
@@ -87,6 +95,8 @@ func (e *exporter) Collect(ch chan<- prometheus.Metric) {
 
 	e.fetchRabbit()
 
+	e.upMetric.Collect(ch)
+
 	for _, gauge := range e.overviewMetrics {
 		gauge.Collect(ch)
 	}

exporter_test.go

@@ -57,4 +57,5 @@ func TestWholeApp(t *testing.T) {
 	expectSubstring(t, body, `rabbitmq_queue_memory{queue="myQueue4",vhost="vhost4"} 13912`)
 	expectSubstring(t, body, `rabbitmq_queue_messages_published_total{queue="myQueue1",vhost="/"} 6`)
 	expectSubstring(t, body, `rabbitmq_queue_disk_writes{queue="myQueue1",vhost="/"} 6`)
+	expectSubstring(t, body, `rabbitmq_up 1`)
 }

metrics.go

@@ -9,6 +9,8 @@ const (
 var (
 	queueLabelNames = []string{"vhost", "queue"}
 
+	upMetricDescription = newMetric("up", "Was the last scrape of rabbitmq successful.")
+
 	overviewMetricDescription = map[string]prometheus.Gauge{
 		"object_totals.channels":    newMetric("channelsTotal", "Total number of open channels."),
 		"object_totals.connections": newMetric("connectionsTotal", "Total number of open connections."),

rabbitClient.go

@@ -1,7 +1,10 @@
 package main
 
 import (
+	"bytes"
 	"encoding/json"
+	"errors"
+	"io/ioutil"
 	"net/http"
 	"time"
 
@@ -10,7 +13,7 @@ import (
 
 var client = &http.Client{Timeout: 10 * time.Second}
 
-func loadMetrics(config rabbitExporterConfig, endpoint string, build func(d *json.Decoder)) {
+func loadMetrics(config rabbitExporterConfig, endpoint string) (*json.Decoder, error) {
 	req, err := http.NewRequest("GET", config.RabbitURL+"/api/"+endpoint, nil)
 	req.SetBasicAuth(config.RabbitUsername, config.RabbitPassword)
 
@@ -22,24 +25,38 @@ func loadMetrics(config rabbitExporterConfig, endpoint string, build func(d *jso
 			status = resp.StatusCode
 		}
 		log.WithFields(log.Fields{"error": err, "host": config.RabbitURL, "statusCode": status}).Error("Error while retrieving data from rabbitHost")
-		return
+		return nil, errors.New("Error while retrieving data from rabbitHost")
 	}
-	build(json.NewDecoder(resp.Body))
+
+	body, err := ioutil.ReadAll(resp.Body)
 	resp.Body.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	return json.NewDecoder(bytes.NewBuffer(body)), nil
 }
 
-func getQueueInfo(config rabbitExporterConfig) []QueueInfo {
+func getQueueInfo(config rabbitExporterConfig) ([]QueueInfo, error) {
 	var q []QueueInfo
-	loadMetrics(config, "queues", func(d *json.Decoder) {
-		q = MakeQueueInfo(d)
-	})
-	return q
+
+	d, err := loadMetrics(config, "queues")
+	if err != nil {
+		return q, err
+	}
+
+	q = MakeQueueInfo(d)
+
+	return q, nil
 }
 
-func getOverviewMap(config rabbitExporterConfig) MetricMap {
+func getOverviewMap(config rabbitExporterConfig) (MetricMap, error) {
 	var overview MetricMap
-	loadMetrics(config, "overview", func(d *json.Decoder) {
-		overview = MakeMap(d)
-	})
-	return overview
+
+	d, err := loadMetrics(config, "overview")
+	if err != nil {
+		return overview, err
+	}
+
+	return MakeMap(d), nil
 }

rabbitClient_test.go

@@ -31,7 +31,7 @@ func TestOverview(t *testing.T) {
 		RabbitURL: server.URL,
 	}
 
-	overview := getOverviewMap(*config)
+	overview, _ := getOverviewMap(*config)
 
 	expect(t, len(overview), 2)
 	expect(t, overview["float1"], 1.23456789101112)
@@ -45,7 +45,7 @@ func TestOverview(t *testing.T) {
 		RabbitURL: errorServer.URL,
 	}
 
-	overview = getOverviewMap(*config)
+	overview, _ = getOverviewMap(*config)
 
 	expect(t, len(overview), 0)
 }
@@ -59,7 +59,7 @@ func TestQueues(t *testing.T) {
 		RabbitURL: server.URL,
 	}
 
-	queues := getQueueInfo(*config)
+	queues, _ := getQueueInfo(*config)
 	expect(t, len(queues), 2)
 	expect(t, queues[0].name, "Queue1")
 	expect(t, queues[0].vhost, "")
@@ -80,7 +80,7 @@ func TestQueues(t *testing.T) {
 		RabbitURL: errorServer.URL,
 	}
 
-	queues = getQueueInfo(*config)
+	queues, _ = getQueueInfo(*config)
 
 	expect(t, len(queues), 0)
 }