Add Prometheus for some Owncast metrics (#1744)

* Add Prometheus for some Owncast metrics. Closes #1303

* Wrap prometheus metrics endpoint in admin middleware

metrics/metrics.go

@@ -2,11 +2,19 @@ package metrics
 
 import (
 	"time"
+
+	"github.com/owncast/owncast/config"
+	"github.com/owncast/owncast/core/data"
+	"github.com/owncast/owncast/models"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
 // How often we poll for updates.
 const metricsPollingInterval = 1 * time.Minute
 
+var _getStatus func() models.Status
+
 // CollectedMetrics stores different collected + timestamped values.
 type CollectedMetrics struct {
 	CPUUtilizations  []timestampedValue `json:"cpu"`
@@ -20,7 +28,48 @@ type CollectedMetrics struct {
 var Metrics *CollectedMetrics
 
 // Start will begin the metrics collection and alerting.
-func Start() {
+func Start(getStatus func() models.Status) {
+	_getStatus = getStatus
+
+	host := data.GetServerURL()
+	if host == "" {
+		host = "unknown"
+	}
+	labels = map[string]string{
+		"version": config.VersionNumber,
+		"host":    host,
+	}
+
+	activeViewerCount = promauto.NewGauge(prometheus.GaugeOpts{
+		Name:        "active_viewer_count",
+		Help:        "The number of viewers.",
+		ConstLabels: labels,
+	})
+
+	activeChatClientCount = promauto.NewGauge(prometheus.GaugeOpts{
+		Name:        "active_chat_client_count",
+		Help:        "The number of connected chat clients.",
+		ConstLabels: labels,
+	})
+
+	chatUserCount = promauto.NewGauge(prometheus.GaugeOpts{
+		Name:        "total_chat_users",
+		Help:        "The total number of chat users on this Owncast instance.",
+		ConstLabels: labels,
+	})
+
+	currentChatMessageCount = promauto.NewGauge(prometheus.GaugeOpts{
+		Name:        "current_chat_message_count",
+		Help:        "The number of chat messages currently saved before cleanup.",
+		ConstLabels: labels,
+	})
+
+	cpuUsage = promauto.NewGauge(prometheus.GaugeOpts{
+		Name:        "cpu_use_pct",
+		Help:        "CPU percentage used as seen within Owncast",
+		ConstLabels: labels,
+	})
+
 	Metrics = new(CollectedMetrics)
 	go startViewerCollectionMetrics()
 	handlePolling()
@@ -35,6 +84,7 @@ func handlePolling() {
 	collectCPUUtilization()
 	collectRAMUtilization()
 	collectDiskUtilization()
+	collectChatClientCount()
 
 	// Alerting
 	handleAlerting()