Record Metrics for Reminder

Signed-off-by: Vyom Yadav <[email protected]>

Author: Vyom-Yadav

internal/reminder/metrics/metrics.go

@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: Copyright 2025 The Minder Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package metrics provides metrics for the reminder service
+package metrics
+
+import (
+	"go.opentelemetry.io/otel/metric"
+)
+
+// Default bucket boundaries in seconds for the delay histograms
+var delayBuckets = []float64{
+	60,    // 1 minute
+	300,   // 5 minutes
+	600,   // 10 minutes
+	1800,  // 30 minutes
+	3600,  // 1 hour
+	7200,  // 2 hours
+	10800, // 3 hours
+	18000, // 5 hours
+	25200, // 7 hours
+	36000, // 10 hours
+}
+
+// Metrics contains all the metrics for the reminder service
+type Metrics struct {
+	// Time between when a reminder became eligible and when it was sent
+	SendDelay metric.Float64Histogram
+
+	// Time between when a reminder became eligible and when it was sent for the first time
+	NewSendDelay metric.Float64Histogram
+
+	// Current number of reminders in the batch
+	BatchSize metric.Int64Histogram
+}
+
+// NewMetrics creates a new metrics instance
+func NewMetrics(meter metric.Meter) (*Metrics, error) {
+	sendDelay, err := meter.Float64Histogram(
+		"send_delay",
+		metric.WithDescription("Time between reminder becoming eligible and actual send (seconds)"),
+		metric.WithUnit("s"),
+		metric.WithExplicitBucketBoundaries(delayBuckets...),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	newSendDelay, err := meter.Float64Histogram(
+		"new_send_delay",
+		metric.WithDescription("Time between reminder becoming eligible and actual send (seconds) for first time reminders"),
+		metric.WithUnit("s"),
+		metric.WithExplicitBucketBoundaries(delayBuckets...),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	batchSize, err := meter.Int64Histogram(
+		"batch_size",
+		metric.WithDescription("Current number of reminders in the batch"),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Metrics{
+		SendDelay:    sendDelay,
+		NewSendDelay: newSendDelay,
+		BatchSize:    batchSize,
+	}, nil
+}

internal/reminder/metrics_server.go

@@ -0,0 +1,94 @@
+// SPDX-FileCopyrightText: Copyright 2025 The Minder Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package reminder
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/rs/zerolog"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/prometheus"
+	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.17.0"
+)
+
+const (
+	metricsPath       = "/metrics"
+	readHeaderTimeout = 2 * time.Second
+)
+
+func (r *reminder) startMetricServer(ctx context.Context) error {
+	logger := zerolog.Ctx(ctx)
+
+	prometheusExporter, err := prometheus.New(
+		prometheus.WithNamespace("reminder"),
+	)
+	if err != nil {
+		return fmt.Errorf("failed to create Prometheus exporter: %w", err)
+	}
+
+	res := resource.NewWithAttributes(
+		semconv.SchemaURL,
+		semconv.ServiceName("reminder"),
+		// TODO: Make this auto-generated
+		semconv.ServiceVersion("v0.1.0"),
+	)
+
+	mp := sdkmetric.NewMeterProvider(
+		sdkmetric.WithReader(prometheusExporter),
+		sdkmetric.WithResource(res),
+	)
+
+	otel.SetMeterProvider(mp)
+
+	mux := http.NewServeMux()
+	mux.Handle(metricsPath, promhttp.Handler())
+
+	server := &http.Server{
+		Addr:              r.cfg.MetricServer.GetAddress(),
+		Handler:           mux,
+		ReadHeaderTimeout: readHeaderTimeout,
+	}
+	logger.Info().Msgf("starting metrics server on %s", server.Addr)
+
+	// Start the metrics server
+	go func() {
+		err = server.ListenAndServe()
+		if err != nil && !errors.Is(err, http.ErrServerClosed) {
+			logger.Err(err).Msg("error starting metrics server")
+		}
+	}()
+
+	// Watch for context cancellation or stop signal to shutdown the metrics server
+	go func() {
+		select {
+		case <-ctx.Done():
+		case <-r.stop:
+		}
+
+		// shutdown the metrics server when either the context is done or when reminder is stopped
+		shutdownCtx, shutdownRelease := context.WithTimeout(context.Background(), 5*time.Second)
+		defer shutdownRelease()
+
+		logger.Info().Msg("shutting down metrics server")
+
+		if err = server.Shutdown(shutdownCtx); err != nil {
+			logger.Err(err).Msg("error shutting down metrics server")
+		}
+
+		if err = mp.Shutdown(shutdownCtx); err != nil {
+			logger.Err(err).Msg("error shutting down metrics provider")
+		}
+
+		close(r.metricsServerDone)
+	}()
+
+	return nil
+}

internal/reminder/reminder.go

@@ -14,9 +14,11 @@ import (
 	"github.com/ThreeDotsLabs/watermill/message"
 	"github.com/google/uuid"
 	"github.com/rs/zerolog"
+	"go.opentelemetry.io/otel"
 
 	"github.com/mindersec/minder/internal/db"
 	remindermessages "github.com/mindersec/minder/internal/reminder/messages"
+	"github.com/mindersec/minder/internal/reminder/metrics"
 	reminderconfig "github.com/mindersec/minder/pkg/config/reminder"
 	"github.com/mindersec/minder/pkg/eventer/constants"
 )
@@ -42,14 +44,18 @@ type reminder struct {
 	ticker *time.Ticker
 
 	eventPublisher message.Publisher
+
+	metrics           *metrics.Metrics
+	metricsServerDone chan struct{}
 }
 
 // NewReminder creates a new reminder instance
 func NewReminder(ctx context.Context, store db.Store, config *reminderconfig.Config) (Interface, error) {
 	r := &reminder{
-		store: store,
-		cfg:   config,
-		stop:  make(chan struct{}),
+		store:             store,
+		cfg:               config,
+		stop:              make(chan struct{}),
+		metricsServerDone: make(chan struct{}),
 	}
 
 	// Set to a random UUID to start
@@ -74,21 +80,40 @@ func (r *reminder) Start(ctx context.Context) error {
 		return errors.New("reminder stopped, cannot start again")
 	default:
 	}
+	// Reminder only stops in case of error or context cancellation
+	// An errored out reminder cannot be started again, so it is stopped here
+	// This also prevents resource leaks if user doesn't explicitly stop the reminder
+	defer r.Stop()
 
 	interval := r.cfg.RecurrenceConfig.Interval
 	if interval <= 0 {
 		return fmt.Errorf("invalid interval: %s", r.cfg.RecurrenceConfig.Interval)
 	}
 
+	if r.cfg.MetricsConfig.Enabled {
+		if err := r.startMetricServer(ctx); err != nil {
+			logger.Err(err).Msg("failed to start metrics server")
+		}
+
+		var err error
+		r.metrics, err = metrics.NewMetrics(otel.Meter("reminder"))
+		if err != nil {
+			return err
+		}
+	} else {
+		close(r.metricsServerDone)
+	}
+
 	r.ticker = time.NewTicker(interval)
-	defer r.Stop()
 
 	for {
 		select {
 		case <-ctx.Done():
+			<-r.metricsServerDone
 			logger.Info().Msg("reminder stopped")
 			return nil
 		case <-r.stop:
+			<-r.metricsServerDone
 			logger.Info().Msg("reminder stopped")
 			return nil
 		case <-r.ticker.C:
@@ -120,13 +145,15 @@ func (r *reminder) Stop() {
 			zerolog.Ctx(context.Background()).Error().Err(err).Msg("error closing event publisher")
 		}
 	})
+	// Wait for the metrics server to stop
+	<-r.metricsServerDone
 }
 
 func (r *reminder) sendReminders(ctx context.Context) error {
 	logger := zerolog.Ctx(ctx)
 
 	// Fetch a batch of repositories
-	repos, err := r.getRepositoryBatch(ctx)
+	repos, repoToLastUpdated, err := r.getRepositoryBatch(ctx)
 	if err != nil {
 		return fmt.Errorf("error fetching repository batch: %w", err)
 	}
@@ -143,6 +170,10 @@ func (r *reminder) sendReminders(ctx context.Context) error {
 		return fmt.Errorf("error creating reminder messages: %w", err)
 	}
 
+	if r.metrics != nil {
+		r.metrics.BatchSize.Record(ctx, int64(len(repos)))
+	}
+
 	err = r.eventPublisher.Publish(constants.TopicQueueRepoReminder, messages...)
 	if err != nil {
 		return fmt.Errorf("error publishing messages: %w", err)
@@ -151,13 +182,16 @@ func (r *reminder) sendReminders(ctx context.Context) error {
 	repoIds := make([]uuid.UUID, len(repos))
 	for _, repo := range repos {
 		repoIds = append(repoIds, repo.ID)
-	}
+		if r.metrics != nil {
+			sendDelay := time.Since(repoToLastUpdated[repo.ID]) - r.cfg.RecurrenceConfig.MinElapsed
 
-	// TODO: Collect Metrics
-	// Potential metrics:
-	// - Gauge: Number of reminders in the current batch
-	// - UpDownCounter: Average reminders sent per batch
-	// - Histogram: reminder_last_sent time distribution
+			recorder := r.metrics.SendDelay
+			if !repo.ReminderLastSent.Valid {
+				recorder = r.metrics.NewSendDelay
+			}
+			recorder.Record(ctx, sendDelay.Seconds())
+		}
+	}
 
 	err = r.store.UpdateReminderLastSentForRepositories(ctx, repoIds)
 	if err != nil {
@@ -167,7 +201,7 @@ func (r *reminder) sendReminders(ctx context.Context) error {
 	return nil
 }
 
-func (r *reminder) getRepositoryBatch(ctx context.Context) ([]db.Repository, error) {
+func (r *reminder) getRepositoryBatch(ctx context.Context) ([]db.Repository, map[uuid.UUID]time.Time, error) {
 	logger := zerolog.Ctx(ctx)
 
 	logger.Debug().Msgf("fetching repositories after cursor: %s", r.repositoryCursor)
@@ -176,21 +210,23 @@ func (r *reminder) getRepositoryBatch(ctx context.Context) ([]db.Repository, err
 		Limit: int64(r.cfg.RecurrenceConfig.BatchSize),
 	})
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
-	eligibleRepos, err := r.getEligibleRepositories(ctx, repos)
+	eligibleRepos, eligibleReposLastUpdated, err := r.getEligibleRepositories(ctx, repos)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	logger.Debug().Msgf("%d/%d repositories are eligible for reminders", len(eligibleRepos), len(repos))
 
 	r.updateRepositoryCursor(ctx, repos)
 
-	return eligibleRepos, nil
+	return eligibleRepos, eligibleReposLastUpdated, nil
 }
 
-func (r *reminder) getEligibleRepositories(ctx context.Context, repos []db.Repository) ([]db.Repository, error) {
+func (r *reminder) getEligibleRepositories(ctx context.Context, repos []db.Repository) (
+	[]db.Repository, map[uuid.UUID]time.Time, error,
+) {
 	eligibleRepos := make([]db.Repository, 0, len(repos))
 
 	// We have a slice of repositories, but the sqlc-generated code wants a slice of UUIDs,
@@ -202,11 +238,11 @@ func (r *reminder) getEligibleRepositories(ctx context.Context, repos []db.Repos
 	}
 	oldestRuleEvals, err := r.store.ListOldestRuleEvaluationsByRepositoryId(ctx, repoIds)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	idToLastUpdate := make(map[uuid.UUID]time.Time, len(oldestRuleEvals))
-	for _, times := range oldestRuleEvals {
-		idToLastUpdate[times.RepositoryID] = times.OldestLastUpdated
+	for _, ruleEval := range oldestRuleEvals {
+		idToLastUpdate[ruleEval.RepositoryID] = ruleEval.OldestLastUpdated
 	}
 
 	cutoff := time.Now().Add(-1 * r.cfg.RecurrenceConfig.MinElapsed)
@@ -216,7 +252,7 @@ func (r *reminder) getEligibleRepositories(ctx context.Context, repos []db.Repos
 		}
 	}
 
-	return eligibleRepos, nil
+	return eligibleRepos, idToLastUpdate, nil
 }
 
 func (r *reminder) updateRepositoryCursor(ctx context.Context, repos []db.Repository) {

internal/reminder/reminder_test.go

@@ -159,7 +159,7 @@ func Test_getRepositoryBatch(t *testing.T) {
 
 			r := createTestReminder(t, store, cfg)
 
-			got, err := r.getRepositoryBatch(context.Background())
+			got, _, err := r.getRepositoryBatch(context.Background())
 			if test.err != "" {
 				require.ErrorContains(t, err, test.err)
 				return

pkg/config/reminder/config.go

@@ -18,10 +18,12 @@ import (
 
 // Config contains the configuration for the reminder service
 type Config struct {
-	Database         config.DatabaseConfig    `mapstructure:"database"`
-	RecurrenceConfig RecurrenceConfig         `mapstructure:"recurrence"`
-	EventConfig      serverconfig.EventConfig `mapstructure:"events"`
-	LoggingConfig    LoggingConfig            `mapstructure:"logging"`
+	Database         config.DatabaseConfig           `mapstructure:"database"`
+	RecurrenceConfig RecurrenceConfig                `mapstructure:"recurrence"`
+	EventConfig      serverconfig.EventConfig        `mapstructure:"events"`
+	LoggingConfig    LoggingConfig                   `mapstructure:"logging"`
+	MetricsConfig    serverconfig.MetricsConfig      `mapstructure:"metrics"`
+	MetricServer     serverconfig.MetricServerConfig `mapstructure:"metric_server" default:"{\"port\":\"9091\"}"`
 }
 
 // Validate validates the configuration