Reduce number of global variables used

This is the first step to make the exporter more testable.

collector/attributes.go

@@ -7,12 +7,9 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 )
 
-var (
-	attributes *prometheus.GaugeVec
-)
-
 type attributesCollector struct {
 	config Config
+	metric *prometheus.GaugeVec
 }
 
 func init() {
@@ -22,28 +19,28 @@ func init() {
 // Takes a config struct and prometheus registry and returns a new Collector exposing
 // labels from the config.
 func NewAttributesCollector(config Config) (Collector, error) {
-	c := attributesCollector{
-		config: config,
-	}
 	labelNames := []string{}
-	for l := range c.config.Attributes {
+	for l := range config.Attributes {
 		labelNames = append(labelNames, l)
 	}
-	attributes = prometheus.NewGaugeVec(
-		prometheus.GaugeOpts{
-			Namespace: Namespace,
-			Name:      "attributes",
-			Help:      "The node_exporter attributes.",
-		},
-		labelNames,
-	)
-	return &c, nil
+
+	return &attributesCollector{
+		config: config,
+		metric: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Namespace: Namespace,
+				Name:      "attributes",
+				Help:      "The node_exporter attributes.",
+			},
+			labelNames,
+		),
+	}, nil
 }
 
 func (c *attributesCollector) Update(ch chan<- prometheus.Metric) (err error) {
 	glog.V(1).Info("Set node_attributes{%v}: 1", c.config.Attributes)
-	attributes.Reset()
-	attributes.With(c.config.Attributes).Set(1)
-	attributes.Collect(ch)
+	c.metric.Reset()
+	c.metric.With(c.config.Attributes).Set(1)
+	c.metric.Collect(ch)
 	return err
 }