add a handler for /metrics

internal/httpsrv/server.go

@@ -9,6 +9,7 @@ import (
 	ginzap "github.com/gin-contrib/zap"
 	"github.com/gin-gonic/gin"
 	"github.com/jmoiron/sqlx"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.hollow.sh/toolbox/events"
 	"go.hollow.sh/toolbox/ginauth"
 	"go.hollow.sh/toolbox/ginjwt"
@@ -42,6 +43,12 @@ var (
 	noOpAuthMiddleware = &ginauth.MultiTokenMiddleware{}
 )
 
+func getGinPrometheusAdapter(h http.Handler) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		h.ServeHTTP(c.Writer, c.Request)
+	}
+}
+
 func (s *Server) setup() *gin.Engine {
 	var err error
 	authMW := noOpAuthMiddleware
@@ -118,6 +125,8 @@ func (s *Server) setup() *gin.Engine {
 	r.GET("/healthz/liveness", s.livenessCheck)
 	r.GET("/healthz/readiness", s.readinessCheck)
 
+	r.GET("/metrics", getGinPrometheusAdapter(promhttp.Handler()))
+
 	v1 := r.Group("/api/v1")
 	{
 		v1Rtr.Routes(v1)