examples: Follow best practices and established naming conventions (#1650)

* examples: Follow best practices and established naming conventions

This is a nitpick but from my experience and understanding the best
practice for label key naming is to use one word, otherwise using an
underscore. Since this is an example users tend to copy, I think
correcting it might be a good idea.

Signed-off-by: Lili Cosic <cosiclili@gmail.com>

* examples: Switch custom labels example

Signed-off-by: Lili Cosic <cosiclili@gmail.com>

---------

Signed-off-by: Lili Cosic <cosiclili@gmail.com>
Co-authored-by: Kemal Akkoyun <kakkoyun@users.noreply.github.com>

examples/customlabels/main.go

@@ -20,9 +20,11 @@ import (
 	"flag"
 	"log"
 	"net/http"
+	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
@@ -33,12 +35,61 @@ func main() {
 
 	// Create a new registry.
 	reg := prometheus.NewRegistry()
-	prometheus.WrapRegistererWith(prometheus.Labels{"serviceName": "my-service-name"}, reg).MustRegister(
+	reg.MustRegister(
 		collectors.NewGoCollector(),
 		collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
 	)
 
-	// Expose the registered metrics via HTTP.
+	// We should see the following metrics with an extra source label. But
+	// other collectors registered above are expected not to have the extra
+	// label.
+	// See also https://prometheus.io/docs/instrumenting/writing_exporters/#target-labels-not-static-scraped-labels
+	startFireKeeper(prometheus.WrapRegistererWith(prometheus.Labels{"component": "FireKeeper"}, reg))
+	startSparkForge(prometheus.WrapRegistererWith(prometheus.Labels{"component": "SparkForge"}, reg))
+
 	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
 	log.Fatal(http.ListenAndServe(*addr, nil))
 }
+
+func startFireKeeper(reg prometheus.Registerer) {
+	firesMaintained := promauto.With(reg).NewCounter(prometheus.CounterOpts{
+		Name: "fires_maintained_total",
+		Help: "Total number of fires maintained",
+	})
+
+	sparksDistributed := promauto.With(reg).NewCounter(prometheus.CounterOpts{
+		Name: "sparks_distributed_total",
+		Help: "Total number of sparks distributed",
+	})
+
+	go func() {
+		for {
+			time.Sleep(5 * time.Second)
+			firesMaintained.Inc()
+			log.Println("FireKeeper maintained a fire")
+		}
+	}()
+
+	go func() {
+		for {
+			time.Sleep(7 * time.Second)
+			sparksDistributed.Inc()
+			log.Println("FireKeeper distributed a spark")
+		}
+	}()
+}
+
+func startSparkForge(reg prometheus.Registerer) {
+	itemsForged := promauto.With(reg).NewCounter(prometheus.CounterOpts{
+		Name: "items_forged_total",
+		Help: "Total number of items forged",
+	})
+
+	go func() {
+		for {
+			time.Sleep(6 * time.Second)
+			itemsForged.Inc()
+			log.Println("SparkForge forged an item")
+		}
+	}()
+}