Pass host label when option is enabled

modules/caddyhttp/metrics.go

@@ -35,7 +35,7 @@ var httpMetrics = struct {
 func initHTTPMetrics() {
 	const ns, sub = "caddy", "http"
 
-	basicLabels := []string{"server", "handler"}
+	basicLabels := []string{"server", "handler", "host"}
 	httpMetrics.requestInFlight = promauto.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: ns,
 		Subsystem: sub,
@@ -59,7 +59,7 @@ func initHTTPMetrics() {
 	durationBuckets := prometheus.DefBuckets
 	sizeBuckets := prometheus.ExponentialBuckets(256, 4, 8)
 
-	httpLabels := []string{"server", "handler", "code", "method"}
+	httpLabels := []string{"server", "handler", "host", "code", "method"}
 	httpMetrics.requestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: ns,
 		Subsystem: sub,
@@ -103,23 +103,29 @@ func serverNameFromContext(ctx context.Context) string {
 type metricsInstrumentedHandler struct {
 	handler string
 	mh      MiddlewareHandler
+	perHost bool
 }
 
-func newMetricsInstrumentedHandler(handler string, mh MiddlewareHandler) *metricsInstrumentedHandler {
+func newMetricsInstrumentedHandler(handler string, mh MiddlewareHandler, perHost bool) *metricsInstrumentedHandler {
 	httpMetrics.init.Do(func() {
 		initHTTPMetrics()
 	})
 
-	return &metricsInstrumentedHandler{handler, mh}
+	return &metricsInstrumentedHandler{handler, mh, perHost}
 }
 
 func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Request, next Handler) error {
+	host := "*"
+	if h.perHost {
+		host = r.Host
+	}
+
 	server := serverNameFromContext(r.Context())
-	labels := prometheus.Labels{"server": server, "handler": h.handler}
+	labels := prometheus.Labels{"server": server, "handler": h.handler, "host": host}
 	method := metrics.SanitizeMethod(r.Method)
 	// the "code" value is set later, but initialized here to eliminate the possibility
 	// of a panic
-	statusLabels := prometheus.Labels{"server": server, "handler": h.handler, "method": method, "code": ""}
+	statusLabels := prometheus.Labels{"server": server, "handler": h.handler, "host": host, "method": method, "code": ""}
 
 	inFlight := httpMetrics.requestInFlight.With(labels)
 	inFlight.Inc()
@@ -146,7 +152,7 @@ func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Re
 		// probably falling through with an empty handler.
 		if statusLabels["code"] == "" {
 			// we still sanitize it, even though it's likely to be 0. A 200 is
-			// returned on fallthrough so we want to reflect that.
+			// returned on fallthrough, so we want to reflect that.
 			statusLabels["code"] = metrics.SanitizeCode(status)
 		}