feat: add prometheus metrics

backend/db/db.go

@@ -7,6 +7,7 @@ import (
 	"net/url"
 	"os"
 
+	"codeberg.org/u1f320/pronouns.cc/backend/log"
 	"emperror.dev/errors"
 	"github.com/Masterminds/squirrel"
 	"github.com/jackc/pgx/v5/pgconn"
@@ -14,6 +15,7 @@ import (
 	"github.com/mediocregopher/radix/v4"
 	"github.com/minio/minio-go/v7"
 	"github.com/minio/minio-go/v7/pkg/credentials"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 var sq = squirrel.StatementBuilder.PlaceholderFormat(squirrel.Dollar)
@@ -32,19 +34,24 @@ type DB struct {
 	minio       *minio.Client
 	minioBucket string
 	baseURL     *url.URL
+
+	TotalRequests prometheus.Counter
 }
 
 func New() (*DB, error) {
+	log.Debug("creating postgres client")
 	pool, err := pgxpool.New(context.Background(), os.Getenv("DATABASE_URL"))
 	if err != nil {
 		return nil, errors.Wrap(err, "creating postgres client")
 	}
 
+	log.Debug("creating redis client")
 	redis, err := (&radix.PoolConfig{}).New(context.Background(), "tcp", os.Getenv("REDIS"))
 	if err != nil {
 		return nil, errors.Wrap(err, "creating redis client")
 	}
 
+	log.Debug("creating minio client")
 	minioClient, err := minio.New(os.Getenv("MINIO_ENDPOINT"), &minio.Options{
 		Creds:  credentials.NewStaticV4(os.Getenv("MINIO_ACCESS_KEY_ID"), os.Getenv("MINIO_ACCESS_KEY_SECRET"), ""),
 		Secure: os.Getenv("MINIO_SSL") == "true",
@@ -67,6 +74,12 @@ func New() (*DB, error) {
 		baseURL:     baseURL,
 	}
 
+	log.Debug("initializing metrics")
+	err = db.initMetrics()
+	if err != nil {
+		return nil, errors.Wrap(err, "initializing metrics")
+	}
+
 	return db, nil
 }
 

backend/db/metrics.go

@@ -0,0 +1,63 @@
+package db
+
+import (
+	"context"
+
+	"codeberg.org/u1f320/pronouns.cc/backend/log"
+	"emperror.dev/errors"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+func (db *DB) initMetrics() (err error) {
+	err = prometheus.Register(prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+		Name: "pronouns_users_total",
+		Help: "The total number of registered users",
+	}, func() float64 {
+		count, err := db.TotalUserCount(context.Background())
+		if err != nil {
+			log.Errorf("getting user count for metrics: %v", err)
+		}
+		return float64(count)
+	}))
+	if err != nil {
+		return errors.Wrap(err, "registering user count gauge")
+	}
+
+	err = prometheus.Register(prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+		Name: "pronouns_members_total",
+		Help: "The total number of registered members",
+	}, func() float64 {
+		count, err := db.TotalMemberCount(context.Background())
+		if err != nil {
+			log.Errorf("getting member count for metrics: %v", err)
+		}
+		return float64(count)
+	}))
+	if err != nil {
+		return errors.Wrap(err, "registering member count gauge")
+	}
+
+	db.TotalRequests = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "pronouns_api_requests_total",
+		Help: "The total number of API requests since the last restart",
+	})
+
+	return nil
+}
+
+func (db *DB) TotalUserCount(ctx context.Context) (numUsers int64, err error) {
+	err = db.QueryRow(ctx, "SELECT COUNT(*) FROM users WHERE deleted_at IS NULL").Scan(&numUsers)
+	if err != nil {
+		return 0, errors.Wrap(err, "querying user count")
+	}
+	return numUsers, nil
+}
+
+func (db *DB) TotalMemberCount(ctx context.Context) (numMembers int64, err error) {
+	err = db.QueryRow(ctx, "SELECT COUNT(*) FROM members WHERE unlisted = false AND user_id = ANY(SELECT id FROM users WHERE deleted_at IS NULL)").Scan(&numMembers)
+	if err != nil {
+		return 0, errors.Wrap(err, "querying member count")
+	}
+	return numMembers, nil
+}

backend/routes/meta/meta.go

@@ -31,13 +31,12 @@ type MetaResponse struct {
 func (s *Server) meta(w http.ResponseWriter, r *http.Request) error {
 	ctx := r.Context()
 
-	var numUsers, numMembers int64
-	err := s.DB.QueryRow(ctx, "SELECT COUNT(*) FROM users WHERE deleted_at IS NULL").Scan(&numUsers)
+	numUsers, err := s.DB.TotalUserCount(ctx)
 	if err != nil {
 		return errors.Wrap(err, "querying user count")
 	}
 
-	err = s.DB.QueryRow(ctx, "SELECT COUNT(*) FROM members WHERE unlisted = false AND user_id = ANY(SELECT id FROM users WHERE deleted_at IS NULL)").Scan(&numMembers)
+	numMembers, err := s.DB.TotalMemberCount(ctx)
 	if err != nil {
 		return errors.Wrap(err, "querying user count")
 	}

backend/routes/mod/routes.go

@@ -6,6 +6,7 @@ import (
 	"codeberg.org/u1f320/pronouns.cc/backend/server"
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/render"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 type Server struct {
@@ -23,6 +24,8 @@ func Mount(srv *server.Server, r chi.Router) {
 		r.Patch("/reports/{id}", server.WrapHandler(s.resolveReport))
 	})
 
+	r.With(MustAdmin).Handle("/metrics", promhttp.Handler())
+
 	r.With(server.MustAuth).Post("/users/{id}/reports", server.WrapHandler(s.createUserReport))
 	r.With(server.MustAuth).Post("/members/{id}/reports", server.WrapHandler(s.createMemberReport))
 

backend/server/server.go

@@ -107,12 +107,17 @@ func New() (*Server, error) {
 	rateLimiter.Scope("*", "/auth/invites", 10)
 	rateLimiter.Scope("POST", "/auth/discord/*", 10)
 
-	// rate limit handling
-	// - 120 req/minute (2/s)
-	// - keyed by Authorization header if valid token is provided, otherwise by IP
-	// - returns rate limit reset info in error
 	s.Router.Use(rateLimiter.Handler())
 
+	// increment the total requests counter whenever a request is made
+	s.Router.Use(func(next http.Handler) http.Handler {
+		fn := func(w http.ResponseWriter, r *http.Request) {
+			s.DB.TotalRequests.Inc()
+			next.ServeHTTP(w, r)
+		}
+		return http.HandlerFunc(fn)
+	})
+
 	// return an API error for not found + method not allowed
 	s.Router.NotFound(func(w http.ResponseWriter, r *http.Request) {
 		render.Status(r, errCodeStatuses[ErrNotFound])