Antrea Prometheus integration (antrea-io#236)

Integrate with Prometheus monitoring solution.
Integration of the Prometheus client into Antrea controller and agent
allows the exposure of various metrics to Prometheus server.
In addition to Antrea's own set of metrics, Prometheus client will also
expose metrics which are defined by various components which are part of
the Antrea ecosystem, e.g golang, Prometheus itself etc.

cmd/antrea-controller/controller.go

@@ -16,7 +16,6 @@ package main
 
 import (
 	"fmt"
-	"github.com/prometheus/common/log"
 	"net"
 	"net/http"
 	"os"
@@ -141,7 +140,7 @@ func createPrometheusMetricsListener(prometheusHost string,
 
 	err = http.ListenAndServe(net.JoinHostPort(prometheusHost, prometheusPort), nil)
 	if err != nil {
-		klog.Error("Failed to initialize Prometheus metrics server %v", err)
+		klog.Errorf("Failed to initialize Prometheus metrics server %v", err)
 	}
 }
 

pkg/agent/metrics/prometheus.go

@@ -122,6 +122,6 @@ func StartListener(
 
 	err = http.ListenAndServe(net.JoinHostPort(prometheusHost, strconv.Itoa(prometheusPort)), nil)
 	if err != nil {
-		klog.Error("Failed to initialize Prometheus metrics server %v", err)
+		klog.Errorf("Failed to initialize Prometheus metrics server %v", err)
 	}
 }