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
+}