feat(metrics): add scheduler related metrics (#2076)

Signed-off-by: Alexei Dodon <adodon@cisco.com>

pkg/api/controller.go

@@ -377,7 +377,7 @@ func (c *Controller) Shutdown() {
 }
 
 func (c *Controller) StartBackgroundTasks(reloadCtx context.Context) {
-	c.taskScheduler = scheduler.NewScheduler(c.Config, c.Log)
+	c.taskScheduler = scheduler.NewScheduler(c.Config, c.Metrics, c.Log)
 	c.taskScheduler.RunScheduler(reloadCtx)
 
 	// Enable running garbage-collect periodically for DefaultStore

pkg/api/cookiestore.go

@@ -3,6 +3,7 @@ package api
 import (
 	"context"
 	"encoding/gob"
+	"fmt"
 	"io/fs"
 	"os"
 	"path"
@@ -157,3 +158,12 @@ func (cleanTask *CleanTask) DoWork(ctx context.Context) error {
 
 	return nil
 }
+
+func (cleanTask *CleanTask) String() string {
+	return fmt.Sprintf("{Name: %s, sessions: %s}",
+		cleanTask.Name(), cleanTask.sessions)
+}
+
+func (cleanTask *CleanTask) Name() string {
+	return "SessionCleanupTask"
+}

pkg/exporter/api/controller_test.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"math/big"
 	"net/http"
+	"runtime"
 	"strings"
 	"sync"
 	"testing"
@@ -25,6 +26,7 @@ import (
 	zotcfg "zotregistry.io/zot/pkg/api/config"
 	"zotregistry.io/zot/pkg/exporter/api"
 	"zotregistry.io/zot/pkg/extensions/monitoring"
+	"zotregistry.io/zot/pkg/scheduler"
 	. "zotregistry.io/zot/pkg/test/common"
 )
 
@@ -69,12 +71,22 @@ func readDefaultMetrics(collector *api.Collector, chMetric chan prometheus.Metri
 	So(err, ShouldBeNil)
 	So(*metric.Gauge.Value, ShouldEqual, 1)
 
+	pmMetric = <-chMetric
+	So(pmMetric.Desc().String(), ShouldEqual, collector.MetricsDesc["zot_scheduler_workers_total"].String())
+
+	err = pmMetric.Write(&metric)
+	So(err, ShouldBeNil)
+	So(*metric.Gauge.Value, ShouldEqual, runtime.NumCPU()*scheduler.NumWorkersMultiplier)
+
 	pmMetric = <-chMetric
 	So(pmMetric.Desc().String(), ShouldEqual, collector.MetricsDesc["zot_info"].String())
 
 	err = pmMetric.Write(&metric)
 	So(err, ShouldBeNil)
 	So(*metric.Gauge.Value, ShouldEqual, 0)
+
+	pmMetric = <-chMetric
+	So(pmMetric.Desc().String(), ShouldEqual, collector.MetricsDesc["zot_scheduler_generators_total"].String())
 }
 
 func TestNewExporter(t *testing.T) {

pkg/extensions/extension_userprefs_disable.go

@@ -18,6 +18,6 @@ func IsBuiltWithUserPrefsExtension() bool {
 func SetupUserPreferencesRoutes(config *config.Config, router *mux.Router,
 	metaDB mTypes.MetaDB, log log.Logger,
 ) {
-	log.Warn().Msg("userprefs extension is disabled because given zot binary doesn't" +
+	log.Warn().Msg("userprefs extension is disabled because given zot binary doesn't " +
 		"include this feature please build a binary that does so")
 }

pkg/extensions/imagetrust/image_trust.go

@@ -5,6 +5,7 @@ package imagetrust
 
 import (
 	"context"
+	"fmt"
 	"time"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
@@ -274,3 +275,13 @@ func (validityT *validityTask) DoWork(ctx context.Context) error {
 
 	return nil
 }
+
+func (validityT *validityTask) String() string {
+	return fmt.Sprintf("{sigValidityTaskGenerator: %s, repo: %s}",
+		"signatures validity task", // description of generator's task purpose
+		validityT.repo.Name)
+}
+
+func (validityT *validityTask) Name() string {
+	return "SignatureValidityTask"
+}

pkg/extensions/monitoring/extension.go

@@ -83,6 +83,53 @@ var (
 		},
 		[]string{"storageName", "lockType"},
 	)
+	schedulerGenerators = promauto.NewCounter( //nolint: gochecknoglobals
+		prometheus.CounterOpts{
+			Namespace: metricsNamespace,
+			Name:      "scheduler_generators_total",
+			Help:      "Total number of generators registered in scheduler",
+		},
+	)
+	schedulerGeneratorsStatus = promauto.NewGaugeVec( //nolint: gochecknoglobals
+		prometheus.GaugeOpts{
+			Namespace: metricsNamespace,
+			Name:      "scheduler_generators_status",
+			Help:      "Scheduler generators by priority & state",
+		},
+		[]string{"priority", "state"},
+	)
+	schedulerNumWorkers = promauto.NewGauge( //nolint: gochecknoglobals
+		prometheus.GaugeOpts{ //nolint: promlinter
+			Namespace: metricsNamespace,
+			Name:      "scheduler_workers_total",
+			Help:      "Total number of available workers to perform scheduler tasks",
+		},
+	)
+	schedulerWorkers = promauto.NewGaugeVec( //nolint: gochecknoglobals
+		prometheus.GaugeOpts{
+			Namespace: metricsNamespace,
+			Name:      "scheduler_workers",
+			Help:      "Scheduler workers state",
+		},
+		[]string{"state"},
+	)
+	schedulerTasksQueue = promauto.NewGaugeVec( //nolint: gochecknoglobals
+		prometheus.GaugeOpts{
+			Namespace: metricsNamespace,
+			Name:      "scheduler_tasksqueue_length",
+			Help:      "Number of tasks waiting in the queue to pe processed by scheduler workers",
+		},
+		[]string{"priority"},
+	)
+	workersTasksDuration = promauto.NewHistogramVec( //nolint: gochecknoglobals
+		prometheus.HistogramOpts{
+			Namespace: metricsNamespace,
+			Name:      "scheduler_workers_tasks_duration_seconds",
+			Help:      "How long it takes for a worker to execute a task",
+			Buckets:   GetDefaultBuckets(),
+		},
+		[]string{"name"},
+	)
 )
 
 type metricServer struct {
@@ -169,7 +216,7 @@ func IncDownloadCounter(ms MetricServer, repo string) {
 }
 
 func SetStorageUsage(ms MetricServer, rootDir, repo string) {
-	ms.SendMetric(func() {
+	ms.ForceSendMetric(func() {
 		dir := path.Join(rootDir, repo)
 		repoSize, err := GetDirSize(dir)
 
@@ -196,3 +243,47 @@ func ObserveStorageLockLatency(ms MetricServer, latency time.Duration, storageNa
 		storageLockLatency.WithLabelValues(storageName, lockType).Observe(latency.Seconds())
 	})
 }
+
+func IncSchedulerGenerators(ms MetricServer) {
+	ms.ForceSendMetric(func() {
+		schedulerGenerators.Inc()
+	})
+}
+
+func SetSchedulerGenerators(ms MetricServer, gen map[string]map[string]uint64) {
+	ms.SendMetric(func() {
+		for priority, states := range gen {
+			for state, value := range states {
+				schedulerGeneratorsStatus.WithLabelValues(priority, state).Set(float64(value))
+			}
+		}
+	})
+}
+
+func SetSchedulerNumWorkers(ms MetricServer, total int) {
+	ms.SendMetric(func() {
+		schedulerNumWorkers.Set(float64(total))
+	})
+}
+
+func SetSchedulerWorkers(ms MetricServer, w map[string]int) {
+	ms.SendMetric(func() {
+		for state, value := range w {
+			schedulerWorkers.WithLabelValues(state).Set(float64(value))
+		}
+	})
+}
+
+func SetSchedulerTasksQueue(ms MetricServer, tq map[string]int) {
+	ms.SendMetric(func() {
+		for priority, value := range tq {
+			schedulerTasksQueue.WithLabelValues(priority).Set(float64(value))
+		}
+	})
+}
+
+func ObserveWorkersTasksDuration(ms MetricServer, taskName string, duration time.Duration) {
+	ms.SendMetric(func() {
+		workersTasksDuration.WithLabelValues(taskName).Observe(duration.Seconds())
+	})
+}

pkg/extensions/monitoring/minimal.go

@@ -18,17 +18,23 @@ import (
 const (
 	metricsNamespace = "zot"
 	// Counters.
-	httpConnRequests = metricsNamespace + ".http.requests"
-	repoDownloads    = metricsNamespace + ".repo.downloads"
-	repoUploads      = metricsNamespace + ".repo.uploads"
+	httpConnRequests    = metricsNamespace + ".http.requests"
+	repoDownloads       = metricsNamespace + ".repo.downloads"
+	repoUploads         = metricsNamespace + ".repo.uploads"
+	schedulerGenerators = metricsNamespace + ".scheduler.generators"
 	// Gauge.
-	repoStorageBytes = metricsNamespace + ".repo.storage.bytes"
-	serverInfo       = metricsNamespace + ".info"
+	repoStorageBytes          = metricsNamespace + ".repo.storage.bytes"
+	serverInfo                = metricsNamespace + ".info"
+	schedulerNumWorkers       = metricsNamespace + ".scheduler.workers.total"
+	schedulerWorkers          = metricsNamespace + ".scheduler.workers"
+	schedulerGeneratorsStatus = metricsNamespace + ".scheduler.generators.status"
+	schedulerTasksQueue       = metricsNamespace + ".scheduler.tasksqueue.length"
 	// Summary.
 	httpRepoLatencySeconds = metricsNamespace + ".http.repo.latency.seconds"
 	// Histogram.
 	httpMethodLatencySeconds  = metricsNamespace + ".http.method.latency.seconds"
 	storageLockLatencySeconds = metricsNamespace + ".storage.lock.latency.seconds"
+	workersTasksDuration      = metricsNamespace + ".scheduler.workers.tasks.duration.seconds"
 
 	metricsScrapeTimeout       = 2 * time.Minute
 	metricsScrapeCheckInterval = 30 * time.Second
@@ -39,7 +45,7 @@ type metricServer struct {
 	lastCheck  time.Time
 	reqChan    chan interface{}
 	cache      *MetricsInfo
-	cacheChan  chan *MetricsInfo
+	cacheChan  chan MetricsCopy
 	bucketsF2S map[float64]string // float64 to string conversion of buckets label
 	log        log.Logger
 	lock       *sync.RWMutex
@@ -51,6 +57,12 @@ type MetricsInfo struct {
 	Summaries  []*SummaryValue
 	Histograms []*HistogramValue
 }
+type MetricsCopy struct {
+	Counters   []CounterValue
+	Gauges     []GaugeValue
+	Summaries  []SummaryValue
+	Histograms []HistogramValue
+}
 
 // CounterValue stores info about a metric that is incremented over time,
 // such as the number of requests to an HTTP endpoint.
@@ -118,7 +130,7 @@ func (ms *metricServer) ReceiveMetrics() interface{} {
 		ms.enabled = true
 	}
 	ms.lock.Unlock()
-	ms.cacheChan <- &MetricsInfo{}
+	ms.cacheChan <- MetricsCopy{}
 
 	return <-ms.cacheChan
 }
@@ -145,7 +157,29 @@ func (ms *metricServer) Run() {
 		select {
 		case <-ms.cacheChan:
 			ms.lastCheck = time.Now()
-			ms.cacheChan <- ms.cache
+			// make a copy of cache values to prevent data race
+			metrics := MetricsCopy{
+				Counters:   make([]CounterValue, len(ms.cache.Counters)),
+				Gauges:     make([]GaugeValue, len(ms.cache.Gauges)),
+				Summaries:  make([]SummaryValue, len(ms.cache.Summaries)),
+				Histograms: make([]HistogramValue, len(ms.cache.Histograms)),
+			}
+			for i, cv := range ms.cache.Counters {
+				metrics.Counters[i] = *cv
+			}
+
+			for i, gv := range ms.cache.Gauges {
+				metrics.Gauges[i] = *gv
+			}
+
+			for i, sv := range ms.cache.Summaries {
+				metrics.Summaries[i] = *sv
+			}
+
+			for i, hv := range ms.cache.Histograms {
+				metrics.Histograms[i] = *hv
+			}
+			ms.cacheChan <- metrics
 		case m := <-ms.reqChan:
 			switch v := m.(type) {
 			case CounterValue:
@@ -200,7 +234,7 @@ func NewMetricsServer(enabled bool, log log.Logger) MetricServer {
 	ms := &metricServer{
 		enabled:    enabled,
 		reqChan:    make(chan interface{}),
-		cacheChan:  make(chan *MetricsInfo),
+		cacheChan:  make(chan MetricsCopy),
 		cache:      mi,
 		bucketsF2S: bucketsFloat2String,
 		log:        log,
@@ -215,16 +249,21 @@ func NewMetricsServer(enabled bool, log log.Logger) MetricServer {
 // contains a map with key=CounterName and value=CounterLabels.
 func GetCounters() map[string][]string {
 	return map[string][]string{
-		httpConnRequests: {"method", "code"},
-		repoDownloads:    {"repo"},
-		repoUploads:      {"repo"},
+		httpConnRequests:    {"method", "code"},
+		repoDownloads:       {"repo"},
+		repoUploads:         {"repo"},
+		schedulerGenerators: {},
 	}
 }
 
 func GetGauges() map[string][]string {
 	return map[string][]string{
-		repoStorageBytes: {"repo"},
-		serverInfo:       {"commit", "binaryType", "goVersion", "version"},
+		repoStorageBytes:          {"repo"},
+		serverInfo:                {"commit", "binaryType", "goVersion", "version"},
+		schedulerNumWorkers:       {},
+		schedulerGeneratorsStatus: {"priority", "state"},
+		schedulerTasksQueue:       {"priority"},
+		schedulerWorkers:          {"state"},
 	}
 }
 
@@ -238,6 +277,7 @@ func GetHistograms() map[string][]string {
 	return map[string][]string{
 		httpMethodLatencySeconds:  {"method"},
 		storageLockLatencySeconds: {"storageName", "lockType"},
+		workersTasksDuration:      {"name"},
 	}
 }
 
@@ -533,3 +573,66 @@ func GetBuckets(metricName string) []float64 {
 		return GetDefaultBuckets()
 	}
 }
+
+func SetSchedulerNumWorkers(ms MetricServer, workers int) {
+	numWorkers := GaugeValue{
+		Name:  schedulerNumWorkers,
+		Value: float64(workers),
+	}
+	ms.ForceSendMetric(numWorkers)
+}
+
+func IncSchedulerGenerators(ms MetricServer) {
+	genCounter := CounterValue{
+		Name: schedulerGenerators,
+	}
+	ms.ForceSendMetric(genCounter)
+}
+
+func ObserveWorkersTasksDuration(ms MetricServer, taskName string, duration time.Duration) {
+	h := HistogramValue{
+		Name:        workersTasksDuration,
+		Sum:         duration.Seconds(), // convenient temporary store for Histogram latency value
+		LabelNames:  []string{"name"},
+		LabelValues: []string{taskName},
+	}
+	ms.SendMetric(h)
+}
+
+func SetSchedulerGenerators(ms MetricServer, gen map[string]map[string]uint64) {
+	for priority, states := range gen {
+		for state, value := range states {
+			generator := GaugeValue{
+				Name:        schedulerGeneratorsStatus,
+				Value:       float64(value),
+				LabelNames:  []string{"priority", "state"},
+				LabelValues: []string{priority, state},
+			}
+			ms.SendMetric(generator)
+		}
+	}
+}
+
+func SetSchedulerTasksQueue(ms MetricServer, tq map[string]int) {
+	for priority, value := range tq {
+		tasks := GaugeValue{
+			Name:        schedulerTasksQueue,
+			Value:       float64(value),
+			LabelNames:  []string{"priority"},
+			LabelValues: []string{priority},
+		}
+		ms.SendMetric(tasks)
+	}
+}
+
+func SetSchedulerWorkers(ms MetricServer, w map[string]int) {
+	for state, value := range w {
+		workers := GaugeValue{
+			Name:        schedulerWorkers,
+			Value:       float64(value),
+			LabelNames:  []string{"state"},
+			LabelValues: []string{state},
+		}
+		ms.SendMetric(workers)
+	}
+}

pkg/extensions/monitoring/monitoring_test.go

@@ -461,7 +461,8 @@ func TestPopulateStorageMetrics(t *testing.T) {
 		err = WriteImageToFileSystem(CreateDefaultImage(), "busybox", "0.0.1", srcStorageCtlr)
 		So(err, ShouldBeNil)
 
-		sch := scheduler.NewScheduler(conf, ctlr.Log)
+		metrics := monitoring.NewMetricsServer(true, ctlr.Log)
+		sch := scheduler.NewScheduler(conf, metrics, ctlr.Log)
 		ctx, cancel := context.WithCancel(context.Background())
 		sch.RunScheduler(ctx)
 

pkg/extensions/scrub/scrub.go

@@ -63,3 +63,13 @@ func NewTask(imgStore storageTypes.ImageStore, repo string, log log.Logger) *Tas
 func (scrubT *Task) DoWork(ctx context.Context) error {
 	return RunScrubRepo(ctx, scrubT.imgStore, scrubT.repo, scrubT.log) //nolint: contextcheck
 }
+
+func (scrubT *Task) String() string {
+	return fmt.Sprintf("{taskGenerator: \"%s\", repo: \"%s\"}",
+		"image scrub", // description of generator's task purpose
+		scrubT.repo)
+}
+
+func (scrubT *Task) Name() string {
+	return "ScrubTask"
+}

pkg/extensions/search/cve/scan.go

@@ -2,6 +2,7 @@ package cveinfo
 
 import (
 	"context"
+	"fmt"
 	"sync"
 
 	"zotregistry.io/zot/pkg/log"
@@ -194,3 +195,12 @@ func (st *scanTask) DoWork(ctx context.Context) error {
 
 	return nil
 }
+
+func (st *scanTask) String() string {
+	return fmt.Sprintf("{Name: \"%s\", repo: \"%s\", digest: \"%s\"}",
+		st.Name(), st.repo, st.digest)
+}
+
+func (st *scanTask) Name() string {
+	return "ScanTask"
+}

pkg/extensions/search/cve/scan_test.go

@@ -57,7 +57,8 @@ func TestScanGeneratorWithMockedData(t *testing.T) { //nolint: gocyclo
 
 		cfg := config.New()
 		cfg.Scheduler = &config.SchedulerConfig{NumWorkers: 3}
-		sch := scheduler.NewScheduler(cfg, logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(cfg, metrics, logger)
 
 		params := boltdb.DBParameters{
 			RootDir: t.TempDir(),
@@ -502,8 +503,9 @@ func TestScanGeneratorWithRealData(t *testing.T) {
 		metaDB, err := boltdb.New(boltDriver, logger)
 		So(err, ShouldBeNil)
 
+		metrics := monitoring.NewMetricsServer(true, logger)
 		imageStore := local.NewImageStore(rootDir, false, false,
-			logger, monitoring.NewMetricsServer(false, logger), nil, nil)
+			logger, metrics, nil, nil)
 		storeController := storage.StoreController{DefaultStore: imageStore}
 
 		image := CreateRandomVulnerableImage()
@@ -520,7 +522,7 @@ func TestScanGeneratorWithRealData(t *testing.T) {
 
 		So(scanner.IsResultCached(image.DigestStr()), ShouldBeFalse)
 
-		sch := scheduler.NewScheduler(cfg, logger)
+		sch := scheduler.NewScheduler(cfg, metrics, logger)
 
 		generator := cveinfo.NewScanTaskGenerator(metaDB, scanner, logger)
 

pkg/extensions/search/cve/update.go

@@ -2,6 +2,7 @@ package cveinfo
 
 import (
 	"context"
+	"fmt"
 	"sync"
 	"time"
 
@@ -118,3 +119,11 @@ func (dbt *dbUpdateTask) DoWork(ctx context.Context) error {
 
 	return nil
 }
+
+func (dbt *dbUpdateTask) String() string {
+	return fmt.Sprintf("{Name: %s}", dbt.Name())
+}
+
+func (dbt *dbUpdateTask) Name() string {
+	return "DBUpdateTask"
+}

pkg/extensions/search/cve/update_test.go

@@ -14,6 +14,7 @@ import (
 	. "github.com/smartystreets/goconvey/convey"
 
 	"zotregistry.io/zot/pkg/api/config"
+	"zotregistry.io/zot/pkg/extensions/monitoring"
 	cveinfo "zotregistry.io/zot/pkg/extensions/search/cve"
 	"zotregistry.io/zot/pkg/log"
 	mTypes "zotregistry.io/zot/pkg/meta/types"
@@ -37,7 +38,8 @@ func TestCVEDBGenerator(t *testing.T) {
 
 		cfg := config.New()
 		cfg.Scheduler = &config.SchedulerConfig{NumWorkers: 3}
-		sch := scheduler.NewScheduler(cfg, logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(cfg, metrics, logger)
 
 		metaDB := &mocks.MetaDBMock{
 			GetRepoMetaFn: func(ctx context.Context, repo string) (mTypes.RepoMeta, error) {

pkg/extensions/sync/sync.go

@@ -5,6 +5,7 @@ package sync
 
 import (
 	"context"
+	"fmt"
 
 	"github.com/containers/common/pkg/retry"
 	"github.com/containers/image/v5/types"
@@ -137,3 +138,12 @@ func newSyncRepoTask(repo string, service Service) *syncRepoTask {
 func (srt *syncRepoTask) DoWork(ctx context.Context) error {
 	return srt.service.SyncRepo(ctx, srt.repo)
 }
+
+func (srt *syncRepoTask) String() string {
+	return fmt.Sprintf("{Name: \"%s\", repo: \"%s\"}",
+		srt.Name(), srt.repo)
+}
+
+func (srt *syncRepoTask) Name() string {
+	return "SyncTask"
+}

pkg/scheduler/README.md

@@ -2,9 +2,9 @@
 
 ## What is a generator and how should it be implemented?
 In order to create a new generator (which will generate new tasks one by one) and add it to the scheduler there are 4 methods which should be implemented:
-1. ***GenerateTask() (Task, error)***
+1. ***Next() (Task, error)***
     ```
-    This method should implement the logic for generating a new task. 
+    This method should implement the logic for generating a new task.
     Basically, when this method is called by the scheduler it should return the next task until there are no more tasks to be generated.
     Also, the Task returned by this method should implement DoWork(ctx context.Context) method which should contain the logic that should be executed when this task is run by the scheduler.
     ```
@@ -27,15 +27,28 @@ In order to create a new generator (which will generate new tasks one by one) an
 The scheduler accepts both periodic and non-periodic generators.
 
 To submit a generator to the scheduler, ***SubmitGenerator*** should be called with the implemented generator, interval of time (which should be time.Duration(0) in case of non-periodic generator, or the interval for the periodic generator) and the priority of the tasks which will be generated by this generator as parameters.
-    
+
 Notes:
 
     - A generator should submit only tasks having the same priority
-    - The priority of a task can be: LowPriorirty, MediumPriority or HighPriority
+    - The priority of a task can be: LowPriority, MediumPriority or HighPriority
 
 # How to submit a Task to the scheduler
 
-In order to create a new task and add it to the scheduler ***DoWork(ctx context.Context) error*** is the method that should be implemented. This should contain the logic that should be executed when this task is run by the scheduler.
+In order to create a new task and add it to the scheduler we need to implement below methods:
+
+1. ***DoWork(ctx context.Context) error***
+```
+This should contain the logic that should be executed when this task is run by the scheduler.
+```
+2. ***Name() string***
+```
+Name of the task.
+```
+3. ***String() string***
+```
+Description of the task. Used in debugging to identify executed task.
+```
 
 To submit a task to the scheduler ***SubmitTask*** should be called with the implemented task and the priority of the task as parameters.
 

pkg/scheduler/scheduler.go

@@ -9,11 +9,14 @@ import (
 	"time"
 
 	"zotregistry.io/zot/pkg/api/config"
+	"zotregistry.io/zot/pkg/extensions/monitoring"
 	"zotregistry.io/zot/pkg/log"
 )
 
 type Task interface {
 	DoWork(ctx context.Context) error
+	Name() string
+	String() string
 }
 
 type generatorsPriorityQueue []*generator
@@ -58,25 +61,31 @@ func (pq *generatorsPriorityQueue) Pop() any {
 const (
 	rateLimiterScheduler = 400
 	rateLimit            = 5 * time.Second
-	numWorkersMultiplier = 4
+	NumWorkersMultiplier = 4
+	sendMetricsInterval  = 5 * time.Second
 )
 
 type Scheduler struct {
 	tasksQLow         chan Task
 	tasksQMedium      chan Task
 	tasksQHigh        chan Task
+	tasksDoWork       int
+	tasksLock         *sync.Mutex
 	generators        generatorsPriorityQueue
 	waitingGenerators []*generator
+	doneGenerators    []*generator
 	generatorsLock    *sync.Mutex
 	log               log.Logger
 	RateLimit         time.Duration
 	NumWorkers        int
 	workerChan        chan Task
+	metricsChan       chan struct{}
 	workerWg          *sync.WaitGroup
 	isShuttingDown    atomic.Bool
+	metricServer      monitoring.MetricServer
 }
 
-func NewScheduler(cfg *config.Config, logC log.Logger) *Scheduler {
+func NewScheduler(cfg *config.Config, ms monitoring.MetricServer, logC log.Logger) *Scheduler { //nolint: varnamelen
 	chLow := make(chan Task, rateLimiterScheduler)
 	chMedium := make(chan Task, rateLimiterScheduler)
 	chHigh := make(chan Task, rateLimiterScheduler)
@@ -85,19 +94,25 @@ func NewScheduler(cfg *config.Config, logC log.Logger) *Scheduler {
 	sublogger := logC.With().Str("component", "scheduler").Logger()
 
 	heap.Init(&generatorPQ)
+	// force pushing this metric (for zot minimal metrics are enabled on first scraping)
+	monitoring.SetSchedulerNumWorkers(ms, numWorkers)
 
 	return &Scheduler{
 		tasksQLow:      chLow,
 		tasksQMedium:   chMedium,
 		tasksQHigh:     chHigh,
+		tasksDoWork:    0, // number of tasks that are in working state
+		tasksLock:      new(sync.Mutex),
 		generators:     generatorPQ,
 		generatorsLock: new(sync.Mutex),
 		log:            log.Logger{Logger: sublogger},
 		// default value
-		RateLimit:  rateLimit,
-		NumWorkers: numWorkers,
-		workerChan: make(chan Task, numWorkers),
-		workerWg:   new(sync.WaitGroup),
+		RateLimit:    rateLimit,
+		NumWorkers:   numWorkers,
+		workerChan:   make(chan Task, numWorkers),
+		metricsChan:  make(chan struct{}, 1),
+		workerWg:     new(sync.WaitGroup),
+		metricServer: ms,
 	}
 }
 
@@ -106,19 +121,95 @@ func (scheduler *Scheduler) poolWorker(ctx context.Context) {
 		go func(workerID int) {
 			defer scheduler.workerWg.Done()
 
-			for task := range scheduler.workerChan {
-				scheduler.log.Debug().Int("worker", workerID).Msg("scheduler: starting task")
+			var workStart time.Time
 
-				if err := task.DoWork(ctx); err != nil {
-					scheduler.log.Error().Int("worker", workerID).Err(err).Msg("scheduler: error while executing task")
+			var workDuration time.Duration
+
+			for task := range scheduler.workerChan {
+				// leave below line here (for zot minimal metrics can be enabled on first scraping)
+				metricsEnabled := scheduler.metricServer.IsEnabled()
+				scheduler.log.Debug().Int("worker", workerID).Str("task", task.String()).Msg("scheduler: starting task")
+
+				if metricsEnabled {
+					scheduler.tasksLock.Lock()
+					scheduler.tasksDoWork++
+					scheduler.tasksLock.Unlock()
+					workStart = time.Now()
 				}
 
-				scheduler.log.Debug().Int("worker", workerID).Msg("scheduler: finished task")
+				if err := task.DoWork(ctx); err != nil {
+					scheduler.log.Error().Int("worker", workerID).Str("task", task.String()).Err(err).
+						Msg("scheduler: error while executing task")
+				}
+
+				if metricsEnabled {
+					scheduler.tasksLock.Lock()
+					scheduler.tasksDoWork--
+					scheduler.tasksLock.Unlock()
+					workDuration = time.Since(workStart)
+					monitoring.ObserveWorkersTasksDuration(scheduler.metricServer, task.Name(), workDuration)
+				}
+
+				scheduler.log.Debug().Int("worker", workerID).Str("task", task.String()).Msg("scheduler: finished task")
 			}
 		}(i + 1)
 	}
 }
 
+func (scheduler *Scheduler) metricsWorker() {
+	ticker := time.NewTicker(sendMetricsInterval)
+
+	for {
+		if scheduler.inShutdown() {
+			return
+		}
+		select {
+		case <-scheduler.metricsChan:
+			ticker.Stop()
+
+			return
+		case <-ticker.C:
+			genMap := make(map[string]map[string]uint64)
+			tasksMap := make(map[string]int)
+			// initialize map
+			for _, p := range []Priority{LowPriority, MediumPriority, HighPriority} {
+				priority := p.String()
+				genMap[priority] = make(map[string]uint64)
+
+				for _, s := range []State{Ready, Waiting, Done} {
+					genMap[priority][s.String()] = 0
+				}
+			}
+
+			scheduler.generatorsLock.Lock()
+			generators := append(append(scheduler.generators, scheduler.waitingGenerators...),
+				scheduler.doneGenerators...)
+
+			for _, gen := range generators {
+				p := gen.priority.String()
+				s := gen.getState().String()
+				genMap[p][s]++
+			}
+
+			// tasks queue size by priority
+			tasksMap[LowPriority.String()] = len(scheduler.tasksQLow)
+			tasksMap[MediumPriority.String()] = len(scheduler.tasksQMedium)
+			tasksMap[HighPriority.String()] = len(scheduler.tasksQHigh)
+			scheduler.generatorsLock.Unlock()
+
+			monitoring.SetSchedulerGenerators(scheduler.metricServer, genMap)
+			monitoring.SetSchedulerTasksQueue(scheduler.metricServer, tasksMap)
+			workersMap := make(map[string]int)
+
+			scheduler.tasksLock.Lock()
+			workersMap["idle"] = scheduler.NumWorkers - scheduler.tasksDoWork
+			workersMap["working"] = scheduler.tasksDoWork
+			scheduler.tasksLock.Unlock()
+			monitoring.SetSchedulerWorkers(scheduler.metricServer, workersMap)
+		}
+	}
+}
+
 func (scheduler *Scheduler) Shutdown() {
 	if !scheduler.inShutdown() {
 		scheduler.shutdown()
@@ -133,6 +224,7 @@ func (scheduler *Scheduler) inShutdown() bool {
 
 func (scheduler *Scheduler) shutdown() {
 	close(scheduler.workerChan)
+	close(scheduler.metricsChan)
 	scheduler.isShuttingDown.Store(true)
 }
 
@@ -147,6 +239,9 @@ func (scheduler *Scheduler) RunScheduler(ctx context.Context) {
 	// start worker pool
 	go scheduler.poolWorker(ctx)
 
+	// periodically send metrics
+	go scheduler.metricsWorker()
+
 	go func() {
 		for {
 			select {
@@ -166,7 +261,7 @@ func (scheduler *Scheduler) RunScheduler(ctx context.Context) {
 					if task != nil {
 						// push tasks into worker pool
 						if !scheduler.inShutdown() {
-							scheduler.log.Debug().Msg("scheduler: pushing task into worker pool")
+							scheduler.log.Debug().Str("task", task.String()).Msg("scheduler: pushing task into worker pool")
 							scheduler.workerChan <- task
 						}
 					}
@@ -185,7 +280,7 @@ func (scheduler *Scheduler) pushReadyGenerators() {
 		modified := false
 
 		for i, gen := range scheduler.waitingGenerators {
-			if gen.getState() == ready {
+			if gen.getState() == Ready {
 				gen.done = false
 				heap.Push(&scheduler.generators, gen)
 				scheduler.waitingGenerators = append(scheduler.waitingGenerators[:i], scheduler.waitingGenerators[i+1:]...)
@@ -217,13 +312,15 @@ func (scheduler *Scheduler) generateTasks() {
 
 	var gen *generator
 
-	// check if the generator with highest prioriy is ready to run
-	if scheduler.generators[0].getState() == ready {
+	// check if the generator with highest priority is ready to run
+	if scheduler.generators[0].getState() == Ready {
 		gen = scheduler.generators[0]
 	} else {
 		gen, _ = heap.Pop(&scheduler.generators).(*generator)
-		if gen.getState() == waiting {
+		if gen.getState() == Waiting {
 			scheduler.waitingGenerators = append(scheduler.waitingGenerators, gen)
+		} else if gen.getState() == Done {
+			scheduler.doneGenerators = append(scheduler.doneGenerators, gen)
 		}
 
 		return
@@ -279,7 +376,7 @@ func (scheduler *Scheduler) SubmitTask(task Task, priority Priority) {
 		return
 	}
 
-	// check if the scheduler it's still running in order to add the task to the channel
+	// check if the scheduler is still running in order to add the task to the channel
 	if scheduler.inShutdown() {
 		return
 	}
@@ -302,12 +399,12 @@ const (
 	HighPriority
 )
 
-type state int
+type State int
 
 const (
-	ready state = iota
-	waiting
-	done
+	Ready State = iota
+	Waiting
+	Done
 )
 
 type TaskGenerator interface {
@@ -342,8 +439,6 @@ func (gen *generator) generate(sch *Scheduler) {
 			return
 		}
 
-		task = nextTask
-
 		// check if the generator is done
 		if gen.taskGenerator.IsDone() {
 			gen.done = true
@@ -352,6 +447,8 @@ func (gen *generator) generate(sch *Scheduler) {
 
 			return
 		}
+
+		task = nextTask
 	}
 
 	// check if it's possible to add a new task to the channel
@@ -370,22 +467,22 @@ func (gen *generator) generate(sch *Scheduler) {
 // if the generator is not periodic then it can be done or ready to generate a new task.
 // if the generator is periodic then it can be waiting (finished its work and wait for its interval to pass)
 // or ready to generate a new task.
-func (gen *generator) getState() state {
+func (gen *generator) getState() State {
 	if gen.interval == time.Duration(0) {
 		if gen.done && gen.remainingTask == nil {
-			return done
+			return Done
 		}
 	} else {
 		if gen.done && time.Since(gen.lastRun) < gen.interval && gen.remainingTask == nil {
-			return waiting
+			return Waiting
 		}
 	}
 
 	if !gen.taskGenerator.IsReady() {
-		return waiting
+		return Waiting
 	}
 
-	return ready
+	return Ready
 }
 
 func (scheduler *Scheduler) SubmitGenerator(taskGenerator TaskGenerator, interval time.Duration, priority Priority) {
@@ -402,6 +499,8 @@ func (scheduler *Scheduler) SubmitGenerator(taskGenerator TaskGenerator, interva
 
 	// add generator to the generators priority queue
 	heap.Push(&scheduler.generators, newGenerator)
+	// force pushing this metric (for zot minimal metrics are enabled on first scraping)
+	monitoring.IncSchedulerGenerators(scheduler.metricServer)
 }
 
 func getNumWorkers(cfg *config.Config) int {
@@ -409,5 +508,39 @@ func getNumWorkers(cfg *config.Config) int {
 		return cfg.Scheduler.NumWorkers
 	}
 
-	return runtime.NumCPU() * numWorkersMultiplier
+	return runtime.NumCPU() * NumWorkersMultiplier
+}
+
+func (p Priority) String() string {
+	var priority string
+
+	switch p {
+	case LowPriority:
+		priority = "low"
+	case MediumPriority:
+		priority = "medium"
+	case HighPriority:
+		priority = "high"
+	default:
+		priority = "invalid"
+	}
+
+	return priority
+}
+
+func (s State) String() string {
+	var status string
+
+	switch s {
+	case Ready:
+		status = "ready"
+	case Waiting:
+		status = "waiting"
+	case Done:
+		status = "done"
+	default:
+		status = "invalid"
+	}
+
+	return status
 }

pkg/scheduler/scheduler_test.go

@@ -12,6 +12,7 @@ import (
 	. "github.com/smartystreets/goconvey/convey"
 
 	"zotregistry.io/zot/pkg/api/config"
+	"zotregistry.io/zot/pkg/extensions/monitoring"
 	"zotregistry.io/zot/pkg/log"
 	"zotregistry.io/zot/pkg/scheduler"
 )
@@ -34,6 +35,14 @@ func (t *task) DoWork(ctx context.Context) error {
 	return nil
 }
 
+func (t *task) String() string {
+	return t.Name()
+}
+
+func (t *task) Name() string {
+	return "TestTask"
+}
+
 type generator struct {
 	log      log.Logger
 	priority string
@@ -100,7 +109,8 @@ func TestScheduler(t *testing.T) {
 		defer os.Remove(logFile.Name()) // clean up
 
 		logger := log.NewLogger("debug", logFile.Name())
-		sch := scheduler.NewScheduler(config.New(), logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(config.New(), metrics, logger)
 
 		genH := &shortGenerator{log: logger, priority: "high priority"}
 		// interval has to be higher than throttle value to simulate
@@ -126,7 +136,8 @@ func TestScheduler(t *testing.T) {
 		logger := log.NewLogger("debug", logFile.Name())
 		cfg := config.New()
 		cfg.Scheduler = &config.SchedulerConfig{NumWorkers: 3}
-		sch := scheduler.NewScheduler(cfg, logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(cfg, metrics, logger)
 
 		genL := &generator{log: logger, priority: "low priority"}
 		sch.SubmitGenerator(genL, time.Duration(0), scheduler.LowPriority)
@@ -160,7 +171,8 @@ func TestScheduler(t *testing.T) {
 		defer os.Remove(logFile.Name()) // clean up
 
 		logger := log.NewLogger("debug", logFile.Name())
-		sch := scheduler.NewScheduler(config.New(), logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(config.New(), metrics, logger)
 
 		t := &task{log: logger, msg: "", err: true}
 		sch.SubmitTask(t, scheduler.MediumPriority)
@@ -184,7 +196,8 @@ func TestScheduler(t *testing.T) {
 		defer os.Remove(logFile.Name()) // clean up
 
 		logger := log.NewLogger("debug", logFile.Name())
-		sch := scheduler.NewScheduler(config.New(), logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(config.New(), metrics, logger)
 
 		genL := &generator{log: logger, priority: "low priority"}
 		sch.SubmitGenerator(genL, 20*time.Millisecond, scheduler.LowPriority)
@@ -208,7 +221,8 @@ func TestScheduler(t *testing.T) {
 		defer os.Remove(logFile.Name()) // clean up
 
 		logger := log.NewLogger("debug", logFile.Name())
-		sch := scheduler.NewScheduler(config.New(), logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(config.New(), metrics, logger)
 
 		t := &task{log: logger, msg: "", err: false}
 		sch.SubmitTask(t, -1)
@@ -225,7 +239,8 @@ func TestScheduler(t *testing.T) {
 		defer os.Remove(logFile.Name()) // clean up
 
 		logger := log.NewLogger("debug", logFile.Name())
-		sch := scheduler.NewScheduler(config.New(), logger)
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(config.New(), metrics, logger)
 
 		ctx, cancel := context.WithCancel(context.Background())
 
@@ -240,11 +255,39 @@ func TestScheduler(t *testing.T) {
 		So(err, ShouldBeNil)
 		So(string(data), ShouldNotContainSubstring, "scheduler: adding a new task")
 	})
+
+	Convey("Test scheduler Priority.String() method", t, func() {
+		var p scheduler.Priority //nolint: varnamelen
+		// test invalid priority
+		p = 6238734
+		So(p.String(), ShouldEqual, "invalid")
+		p = scheduler.LowPriority
+		So(p.String(), ShouldEqual, "low")
+		p = scheduler.MediumPriority
+		So(p.String(), ShouldEqual, "medium")
+		p = scheduler.HighPriority
+		So(p.String(), ShouldEqual, "high")
+	})
+
+	Convey("Test scheduler State.String() method", t, func() {
+		var s scheduler.State //nolint: varnamelen
+		// test invalid state
+		s = -67
+		So(s.String(), ShouldEqual, "invalid")
+		s = scheduler.Ready
+		So(s.String(), ShouldEqual, "ready")
+		s = scheduler.Waiting
+		So(s.String(), ShouldEqual, "waiting")
+		s = scheduler.Done
+		So(s.String(), ShouldEqual, "done")
+	})
 }
 
 func TestGetNumWorkers(t *testing.T) {
 	Convey("Test setting the number of workers - default value", t, func() {
-		sch := scheduler.NewScheduler(config.New(), log.NewLogger("debug", "logFile"))
+		logger := log.NewLogger("debug", "logFile")
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(config.New(), metrics, logger)
 		defer os.Remove("logFile")
 		So(sch.NumWorkers, ShouldEqual, runtime.NumCPU()*4)
 	})
@@ -252,7 +295,9 @@ func TestGetNumWorkers(t *testing.T) {
 	Convey("Test setting the number of workers - getting the value from config", t, func() {
 		cfg := config.New()
 		cfg.Scheduler = &config.SchedulerConfig{NumWorkers: 3}
-		sch := scheduler.NewScheduler(cfg, log.NewLogger("debug", "logFile"))
+		logger := log.NewLogger("debug", "logFile")
+		metrics := monitoring.NewMetricsServer(true, logger)
+		sch := scheduler.NewScheduler(cfg, metrics, logger)
 		defer os.Remove("logFile")
 		So(sch.NumWorkers, ShouldEqual, 3)
 	})

pkg/storage/common/common.go

@@ -1061,6 +1061,15 @@ func (dt *dedupeTask) DoWork(ctx context.Context) error {
 	return err
 }
 
+func (dt *dedupeTask) String() string {
+	return fmt.Sprintf("{Name: %s, digest: %s, dedupe: %t}",
+		dt.Name(), dt.digest, dt.dedupe)
+}
+
+func (dt *dedupeTask) Name() string {
+	return "DedupeTask"
+}
+
 type StorageMetricsInitGenerator struct {
 	ImgStore storageTypes.ImageStore
 	done     bool
@@ -1132,3 +1141,12 @@ func (smt *smTask) DoWork(ctx context.Context) error {
 
 	return nil
 }
+
+func (smt *smTask) String() string {
+	return fmt.Sprintf("{Name: \"%s\", repo: \"%s\"}",
+		smt.Name(), smt.repo)
+}
+
+func (smt *smTask) Name() string {
+	return "StorageMetricsTask"
+}

pkg/storage/gc/gc.go

@@ -851,3 +851,12 @@ func (gct *gcTask) DoWork(ctx context.Context) error {
 	// run task
 	return gct.gc.CleanRepo(ctx, gct.repo) //nolint: contextcheck
 }
+
+func (gct *gcTask) String() string {
+	return fmt.Sprintf("{Name: %s, repo: %s}",
+		gct.Name(), gct.repo)
+}
+
+func (gct *gcTask) Name() string {
+	return "GCTask"
+}

pkg/storage/local/local_test.go

@@ -63,7 +63,9 @@ var DeleteReferrers = config.ImageRetention{ //nolint: gochecknoglobals
 var errCache = errors.New("new cache error")
 
 func runAndGetScheduler() (*scheduler.Scheduler, context.CancelFunc) {
-	taskScheduler := scheduler.NewScheduler(config.New(), zlog.Logger{})
+	log := zlog.Logger{}
+	metrics := monitoring.NewMetricsServer(true, log)
+	taskScheduler := scheduler.NewScheduler(config.New(), metrics, log)
 	taskScheduler.RateLimit = 50 * time.Millisecond
 
 	ctx, cancel := context.WithCancel(context.Background())

pkg/storage/s3/s3_test.go

@@ -62,7 +62,7 @@ func cleanupStorage(store driver.StorageDriver, name string) {
 func createMockStorage(rootDir string, cacheDir string, dedupe bool, store driver.StorageDriver,
 ) storageTypes.ImageStore {
 	log := log.Logger{Logger: zerolog.New(os.Stdout)}
-	metrics := monitoring.NewMetricsServer(false, log)
+	metrics := monitoring.NewMetricsServer(true, log)
 
 	var cacheDriver cache.Cache
 
@@ -187,7 +187,9 @@ func createObjectsStoreDynamo(rootDir string, cacheDir string, dedupe bool, tabl
 }
 
 func runAndGetScheduler() (*scheduler.Scheduler, context.CancelFunc) {
-	taskScheduler := scheduler.NewScheduler(config.New(), log.Logger{})
+	logger := log.Logger{}
+	metrics := monitoring.NewMetricsServer(false, logger)
+	taskScheduler := scheduler.NewScheduler(config.New(), metrics, logger)
 	taskScheduler.RateLimit = 50 * time.Millisecond
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -2048,7 +2050,9 @@ func TestRebuildDedupeIndex(t *testing.T) {
 
 		Convey("Intrerrupt rebuilding and restart, checking idempotency", func() {
 			for i := 0; i < 10; i++ {
-				taskScheduler := scheduler.NewScheduler(config.New(), log.Logger{})
+				logger := log.Logger{}
+				metrics := monitoring.NewMetricsServer(false, logger)
+				taskScheduler := scheduler.NewScheduler(config.New(), metrics, logger)
 				taskScheduler.RateLimit = 1 * time.Millisecond
 
 				ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
@@ -2087,7 +2091,9 @@ func TestRebuildDedupeIndex(t *testing.T) {
 
 			// now from dedupe false to true
 			for i := 0; i < 10; i++ {
-				taskScheduler := scheduler.NewScheduler(config.New(), log.Logger{})
+				logger := log.Logger{}
+				metrics := monitoring.NewMetricsServer(false, logger)
+				taskScheduler := scheduler.NewScheduler(config.New(), metrics, logger)
 				taskScheduler.RateLimit = 1 * time.Millisecond
 
 				ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)