minor context refactor; add metrics

metrics.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	log "github.com/sirupsen/logrus"
+	"net/http"
+)
+
+func (b *BuildManager) setupMetrics(port uint32) {
+	b.metrics.queueSize = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Name: "build_queue_size",
+		Help: "Build queue size",
+	}, []string{"repository", "status"})
+
+	mux := http.NewServeMux()
+	mux.Handle("/", promhttp.Handler())
+	go func() {
+		err := http.ListenAndServe(fmt.Sprintf(":%d", port), mux) //nolint:gosec
+		if err != nil {
+			log.Errorf("failed to start metrics server: %v", err)
+		}
+	}()
+}