Remove usage of global registry from Go example

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

docs/guides/go-application.md

@@ -29,11 +29,18 @@ package main
 import (
 	"net/http"
 
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 func main() {
-        http.Handle("/metrics", promhttp.Handler())
+	reg := prometheus.NewRegistry()
+	reg.MustRegister(
+		collectors.NewGoCollector(),
+		collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
+	)
+	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
 	http.ListenAndServe(":2112", nil)
 }
 ```
@@ -66,26 +73,35 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-func recordMetrics() {
+type metrics struct {
+	opsProcessed prometheus.Counter
+}
+
+func newMetrics(reg prometheus.Registerer) *metrics {
+	m := &metrics{
+		opsProcessed: promauto.With(reg).NewCounter(prometheus.CounterOpts{
+			Name: "myapp_processed_ops_total",
+			Help: "The total number of processed events",
+		}),
+	}
+	return m
+}
+
+func recordMetrics(m *metrics) {
 	go func() {
 		for {
-                        opsProcessed.Inc()
+			m.opsProcessed.Inc()
 			time.Sleep(2 * time.Second)
 		}
 	}()
 }
 
-var (
-        opsProcessed = promauto.NewCounter(prometheus.CounterOpts{
-                Name: "myapp_processed_ops_total",
-                Help: "The total number of processed events",
-        })
-)
-
 func main() {
-        recordMetrics()
+	reg := prometheus.NewRegistry()
+	m := newMetrics(reg)
+	recordMetrics(m)
 
-        http.Handle("/metrics", promhttp.Handler())
+	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
 	http.ListenAndServe(":2112", nil)
 }
 ```

docs/tutorials/instrumenting_http_server_in_go.md

@@ -44,30 +44,42 @@ Now lets add a metric to the server which will instrument the number of requests
 Create a Prometheus counter
 
 ```go
-var pingCounter = prometheus.NewCounter(
+type metrics struct {
+	pingCounter prometheus.Counter
+}
+
+func newMetrics(reg prometheus.Registerer) *metrics {
+	m := &metrics{
+		pingCounter: promauto.With(reg).NewCounter(
 			prometheus.CounterOpts{
 				Name: "ping_request_count",
 				Help: "No of request handled by Ping handler",
-   },
-)
-```
-
-Next lets update the ping Handler to increase the count of the counter using `pingCounter.Inc()`.
-
-```go
-func ping(w http.ResponseWriter, req *http.Request) {
-   pingCounter.Inc()
-   fmt.Fprintf(w, "pong")
+			}),
+	}
+	return m
 }
 ```
 
-Then register the counter to the Default Register and expose the metrics.
+Next lets update the ping Handler to increase the count of the counter using `metrics.pingCounter.Inc()`.
+
+```go
+func ping(m *metrics) func(w http.ResponseWriter, req *http.Request) {
+	return func(w http.ResponseWriter, req *http.Request) {
+		m.pingCounter.Inc()
+		fmt.Fprintf(w, "pong")
+	}
+}
+```
+
+Then register the metrics (in this case only one counter) to a Prometheus Register and expose the metrics.
 
 ```go
 func main() {
-   prometheus.MustRegister(pingCounter)
-   http.HandleFunc("/ping", ping)
-   http.Handle("/metrics", promhttp.Handler())
+	reg := prometheus.NewRegistry()
+	m := newMetrics(reg)
+
+	http.HandleFunc("/ping", ping(m))
+	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
 	http.ListenAndServe(":8090", nil)
 }
 ```
@@ -76,6 +88,7 @@ The `prometheus.MustRegister` function registers the pingCounter to the default
 To expose the metrics the Go Prometheus client library provides the promhttp package.
 `promhttp.Handler()` provides a `http.Handler` which exposes the metrics registered in the Default Register.
 
+The sample code depends on the
 The sample code depends on the
 
 ```go
@@ -86,33 +99,44 @@ import (
 	"net/http"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-var pingCounter = prometheus.NewCounter(
+type metrics struct {
+	pingCounter prometheus.Counter
+}
+
+func newMetrics(reg prometheus.Registerer) *metrics {
+	m := &metrics{
+		pingCounter: promauto.With(reg).NewCounter(
 			prometheus.CounterOpts{
 				Name: "ping_request_count",
 				Help: "No of request handled by Ping handler",
-   },
-)
+			}),
+	}
+	return m
+}
 
-func ping(w http.ResponseWriter, req *http.Request) {
-   pingCounter.Inc()
+func ping(m *metrics) func(w http.ResponseWriter, req *http.Request) {
+	return func(w http.ResponseWriter, req *http.Request) {
+		m.pingCounter.Inc()
 		fmt.Fprintf(w, "pong")
 	}
+}
 
 func main() {
-   prometheus.MustRegister(pingCounter)
+	reg := prometheus.NewRegistry()
+	m := newMetrics(reg)
 
-   http.HandleFunc("/ping", ping)
-   http.Handle("/metrics", promhttp.Handler())
+	http.HandleFunc("/ping", ping(m))
+	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
 	http.ListenAndServe(":8090", nil)
 }
 ```
 
 Run the example
-
-```sh
+```bash
 go mod init prom_example
 go mod tidy
 go run server.go