[#375] Add log metrics

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

cmd/frostfs-ir/main.go

@@ -61,6 +61,7 @@ func main() {
 	cfg, err = newConfig()
 	exitErr(err)
 
+	logPrm.MetricsNamespace = "frostfs-ir"
 	err = logPrm.SetLevelString(
 		cfg.GetString("logger.level"),
 	)

cmd/frostfs-node/config.go

@@ -542,6 +542,8 @@ func initCfg(appCfg *config.Config) *cfg {
 	logPrm, err := c.loggerPrm()
 	fatalOnErr(err)
 
+	logPrm.MetricsNamespace = "frostfs-node"
+
 	log, err := logger.NewLogger(logPrm)
 	fatalOnErr(err)
 

pkg/util/logger/logger.go

@@ -31,6 +31,9 @@ type Prm struct {
 	// support runtime rereading
 	level zapcore.Level
 
+	// MetricsNamespace is the namespace string used for log counter metrics
+	MetricsNamespace string
+
 	// do not support runtime rereading
 }
 
@@ -79,10 +82,15 @@ func NewLogger(prm *Prm) (*Logger, error) {
 
 	lvl := zap.NewAtomicLevelAt(prm.level)
 
+	m := newLogMetrics(prm.MetricsNamespace)
+
 	c := zap.NewProductionConfig()
 	c.Level = lvl
 	c.Encoding = "console"
 	c.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
+	c.Sampling.Hook = func(e zapcore.Entry, sd zapcore.SamplingDecision) {
+		m.Inc(e.Level, sd == zapcore.LogDropped)
+	}
 
 	lZap, err := c.Build(
 		zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel)),

pkg/util/logger/metrics.go

@@ -0,0 +1,37 @@
+package logger
+
+import (
+	"strconv"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-observability/metrics"
+	"github.com/prometheus/client_golang/prometheus"
+	"go.uber.org/zap/zapcore"
+)
+
+const (
+	logSubsystem    = "log"
+	logLevelLabel   = "level"
+	logDroppedLabel = "dropped"
+)
+
+type logMetrics struct {
+	logCount *prometheus.CounterVec
+}
+
+func newLogMetrics(namespace string) *logMetrics {
+	return &logMetrics{
+		logCount: metrics.NewCounterVec(prometheus.CounterOpts{
+			Namespace: namespace,
+			Subsystem: logSubsystem,
+			Name:      "log_count",
+			Help:      "Total log entries emitted or dropped by severity level",
+		}, []string{logLevelLabel, logDroppedLabel}),
+	}
+}
+
+func (m *logMetrics) Inc(level zapcore.Level, dropped bool) {
+	m.logCount.With(prometheus.Labels{
+		logLevelLabel:   level.String(),
+		logDroppedLabel: strconv.FormatBool(dropped),
+	}).Inc()
+}