fix: promtail; clean up metrics generated from logs after a config reload.

clients/pkg/logentry/metric/metricvec.go

@@ -84,6 +84,12 @@ func (c *metricVec) Delete(labels model.LabelSet) bool {
 	return ok
 }
 
+func (c *metricVec) DeleteAll() {
+	c.mtx.Lock()
+	defer c.mtx.Unlock()
+	c.metrics = map[model.Fingerprint]prometheus.Metric{}
+}
+
 // prune will remove all metrics which implement the Expirable interface and have expired
 // it does not take out a lock on the metrics map so whoever calls this function should do so.
 func (c *metricVec) prune() {

clients/pkg/logentry/stages/decolorize.go

@@ -33,3 +33,8 @@ func (m *decolorizeStage) Run(in chan Entry) chan Entry {
 func (m *decolorizeStage) Name() string {
 	return StageTypeDecolorize
 }
+
+// Cleanup implements Stage.
+func (*decolorizeStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/drop.go

@@ -266,3 +266,8 @@ func (m *dropStage) shouldDrop(e Entry) bool {
 func (m *dropStage) Name() string {
 	return StageTypeDrop
 }
+
+// Cleanup implements Stage.
+func (*dropStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/eventlogmessage.go

@@ -142,6 +142,11 @@ func (m *eventLogMessageStage) Name() string {
 	return StageTypeEventLogMessage
 }
 
+// Cleanup implements Stage.
+func (*eventLogMessageStage) Cleanup() {
+	// no-op
+}
+
 // Sanitize a input string to convert it into a valid prometheus label
 // TODO: switch to prometheus/prometheus/util/strutil/SanitizeFullLabelName
 func SanitizeFullLabelName(input string) string {

clients/pkg/logentry/stages/extensions.go

@@ -59,6 +59,11 @@ func (c *cri) Name() string {
 	return "cri"
 }
 
+// Cleanup implements Stage.
+func (*cri) Cleanup() {
+	// no-op
+}
+
 // implements Stage interface
 func (c *cri) Run(entry chan Entry) chan Entry {
 	entry = c.base.Run(entry)

clients/pkg/logentry/stages/geoip.go

@@ -123,6 +123,11 @@ func (g *geoIPStage) Name() string {
 	return StageTypeGeoIP
 }
 
+// Cleanup implements Stage.
+func (*geoIPStage) Cleanup() {
+	// no-op
+}
+
 func (g *geoIPStage) process(labels model.LabelSet, extracted map[string]interface{}, _ *time.Time, _ *string) {
 	var ip net.IP
 	if g.cfgs.Source != nil {

clients/pkg/logentry/stages/json.go

@@ -188,3 +188,8 @@ func (j *jsonStage) processEntry(extracted map[string]interface{}, entry *string
 func (j *jsonStage) Name() string {
 	return StageTypeJSON
 }
+
+// Cleanup implements Stage.
+func (*jsonStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/limit.go

@@ -138,6 +138,11 @@ func (m *limitStage) Name() string {
 	return StageTypeLimit
 }
 
+// Cleanup implements Stage.
+func (*limitStage) Cleanup() {
+	// no-op
+}
+
 func getDropCountByLabelMetric(registerer prometheus.Registerer) *prometheus.CounterVec {
 	return util.RegisterCounterVec(registerer, "logentry", "dropped_lines_by_label_total",
 		"A count of all log lines dropped as a result of a pipeline stage",

clients/pkg/logentry/stages/match.go

@@ -206,3 +206,8 @@ func (m *matcherStage) processLogQL(e Entry) (Entry, bool) {
 func (m *matcherStage) Name() string {
 	return StageTypeMatch
 }
+
+// Cleanup implements Stage.
+func (*matcherStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/metrics.go

@@ -128,11 +128,11 @@ func newMetricStage(logger log.Logger, config interface{}, registry prometheus.R
 			metrics[name] = collector
 		}
 	}
-	return toStage(&metricStage{
+	return &metricStage{
 		logger:  logger,
 		cfg:     *cfgs,
 		metrics: metrics,
-	}), nil
+	}, nil
 }
 
 // metricStage creates and updates prometheus metrics based on extracted pipeline data
@@ -142,6 +142,19 @@ type metricStage struct {
 	metrics map[string]prometheus.Collector
 }
 
+func (m *metricStage) Run(in chan Entry) chan Entry {
+	out := make(chan Entry)
+	go func() {
+		defer close(out)
+
+		for e := range in {
+			m.Process(e.Labels, e.Extracted, &e.Timestamp, &e.Line)
+			out <- e
+		}
+	}()
+	return out
+}
+
 // Process implements Stage
 func (m *metricStage) Process(labels model.LabelSet, extracted map[string]interface{}, _ *time.Time, entry *string) {
 	for name, collector := range m.metrics {
@@ -178,6 +191,20 @@ func (m *metricStage) Name() string {
 	return StageTypeMetric
 }
 
+// Cleanup implements Stage.
+func (m *metricStage) Cleanup() {
+	for _, collector := range m.metrics {
+		switch vec := collector.(type) {
+		case *metric.Counters:
+			vec.DeleteAll()
+		case *metric.Gauges:
+			vec.DeleteAll()
+		case *metric.Histograms:
+			vec.DeleteAll()
+		}
+	}
+}
+
 // recordCounter will update a counter metric
 // nolint:goconst
 func (m *metricStage) recordCounter(name string, counter *metric.Counters, labels model.LabelSet, v interface{}) {

clients/pkg/logentry/stages/metrics_test.go

@@ -127,6 +127,13 @@ func TestMetricsPipeline(t *testing.T) {
 		strings.NewReader(expectedMetrics)); err != nil {
 		t.Fatalf("mismatch metrics: %v", err)
 	}
+
+	pl.Cleanup()
+
+	if err := testutil.GatherAndCompare(registry,
+		strings.NewReader("")); err != nil {
+		t.Fatalf("mismatch metrics: %v", err)
+	}
 }
 
 func TestNegativeGauge(t *testing.T) {
@@ -435,7 +442,7 @@ func TestDefaultIdleDuration(t *testing.T) {
 	if err != nil {
 		t.Fatalf("failed to create stage with metrics: %v", err)
 	}
-	assert.Equal(t, int64(5*time.Minute.Seconds()), ms.(*stageProcessor).Processor.(*metricStage).cfg["total_keys"].maxIdleSec)
+	assert.Equal(t, int64(5*time.Minute.Seconds()), ms.(*metricStage).cfg["total_keys"].maxIdleSec)
 }
 
 var (

clients/pkg/logentry/stages/multiline.go

@@ -229,3 +229,8 @@ func (m *multilineStage) flush(out chan Entry, s *multilineState) {
 func (m *multilineStage) Name() string {
 	return StageTypeMultiline
 }
+
+// Cleanup implements Stage.
+func (*multilineStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/pack.go

@@ -218,3 +218,8 @@ func (m *packStage) pack(e Entry) Entry {
 func (m *packStage) Name() string {
 	return StageTypePack
 }
+
+// Cleanup implements Stage.
+func (*packStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/pipeline.go

@@ -30,6 +30,13 @@ type Pipeline struct {
 	dropCount *prometheus.CounterVec
 }
 
+// Cleanup implements Stage.
+func (p *Pipeline) Cleanup() {
+	for _, s := range p.stages {
+		s.Cleanup()
+	}
+}
+
 // NewPipeline creates a new log entry pipeline from a configuration
 func NewPipeline(logger log.Logger, stgs PipelineStages, jobName *string, registerer prometheus.Registerer) (*Pipeline, error) {
 	st := []Stage{}
@@ -169,6 +176,7 @@ func (p *Pipeline) Wrap(next api.EntryHandler) api.EntryHandler {
 	return api.NewEntryHandler(handlerIn, func() {
 		once.Do(func() { close(handlerIn) })
 		wg.Wait()
+		p.Cleanup()
 	})
 }
 

clients/pkg/logentry/stages/sampling.go

@@ -111,3 +111,8 @@ func (m *samplingStage) randomNumber() uint64 {
 func (m *samplingStage) Name() string {
 	return StageTypeSampling
 }
+
+// Cleanup implements Stage.
+func (*samplingStage) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/stage.go

@@ -62,6 +62,7 @@ type Entry struct {
 type Stage interface {
 	Name() string
 	Run(chan Entry) chan Entry
+	Cleanup()
 }
 
 func (entry *Entry) copy() *Entry {
@@ -228,3 +229,8 @@ func New(logger log.Logger, jobName *string, stageType string,
 	}
 	return creator(params)
 }
+
+// Cleanup implements Stage.
+func (*stageProcessor) Cleanup() {
+	// no-op
+}

clients/pkg/logentry/stages/structuredmetadata.go

@@ -33,6 +33,11 @@ func (s *structuredMetadataStage) Name() string {
 	return StageTypeStructuredMetadata
 }
 
+// Cleanup implements Stage.
+func (*structuredMetadataStage) Cleanup() {
+	// no-op
+}
+
 func (s *structuredMetadataStage) Run(in chan Entry) chan Entry {
 	return RunWith(in, func(e Entry) Entry {
 		processLabelsConfigs(s.logger, e.Extracted, s.cfgs, func(labelName model.LabelName, labelValue model.LabelValue) {

docs/sources/send-data/promtail/configuration.md

@@ -681,7 +681,8 @@ The metrics stage allows for defining metrics from the extracted data.
 
 Created metrics are not pushed to Loki and are instead exposed via Promtail's
 `/metrics` endpoint. Prometheus should be configured to scrape Promtail to be
-able to retrieve the metrics configured by this stage.
+able to retrieve the metrics configured by this stage. 
+If Promtail's configuration is reloaded, all metrics will be reset.
 
 
 ```yaml

docs/sources/send-data/promtail/stages/metrics.md

@@ -13,7 +13,8 @@ The `metrics` stage is an action stage that allows for defining and updating
 metrics based on data from the extracted map. Note that created metrics are not
 pushed to Loki and are instead exposed via Promtail's `/metrics` endpoint.
 Prometheus should be configured to scrape Promtail to be able to retrieve the
-metrics configured by this stage.
+metrics configured by this stage. If Promtail's configuration is reloaded, 
+all metrics will be reset.
 
 ## Schema