Backend: Add logs and metric for when host is redirected (#112373)

pkg/middleware/validate_host.go

@@ -3,11 +3,22 @@ package middleware
 import (
 	"strings"
 
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+
 	contextmodel "github.com/grafana/grafana/pkg/services/contexthandler/model"
 	"github.com/grafana/grafana/pkg/setting"
 	"github.com/grafana/grafana/pkg/web"
 )
 
+var (
+	hostRedirectCounter = promauto.NewCounter(prometheus.CounterOpts{
+		Name:      "host_redirect_total",
+		Help:      "Number of requests redirected due to host header mismatch",
+		Namespace: "grafana",
+	})
+)
+
 func ValidateHostHeader(cfg *setting.Cfg) web.Handler {
 	return func(c *contextmodel.ReqContext) {
 		// ignore local render calls
@@ -21,6 +32,8 @@ func ValidateHostHeader(cfg *setting.Cfg) web.Handler {
 		}
 
 		if !strings.EqualFold(h, cfg.Domain) {
+			hostRedirectCounter.Inc()
+			c.Logger.Info("Enforcing Host header", "hosted", c.Req.Host, "expected", cfg.Domain)
 			c.Redirect(strings.TrimSuffix(cfg.AppURL, "/")+c.Req.RequestURI, 301)
 			return
 		}