Extend metrics library

Details of the goals and implementation of the metrics library are documented
in pkg/metrics/doc.go and in the code doc comments.

Fixes: cilium#2376

Signed-off-by: Anna Kapuscinska <anna@isovalent.com>

pkg/metrics/bpfmetric.go

@@ -3,45 +3,59 @@
 
 package metrics
 
-import "github.com/prometheus/client_golang/prometheus"
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// The interface in this file provides a bridge between the new metrics library
+// and the existing code defining metrics. It's considered deprecated - use the
+// interface from custommetric.go instead.
 
-// BPFMetric represents a metric read directly from a BPF map.
-// It's intended to be used in custom collectors. The interface doesn't provide
-// any validation, so it's up to the collector implementer to guarantee the
-// metrics consistency.
 type BPFMetric interface {
 	Desc() *prometheus.Desc
 	MustMetric(value float64, labelValues ...string) prometheus.Metric
 }
 
 type bpfCounter struct {
-	desc *prometheus.Desc
+	metric *granularCustomCounter[NilLabels]
 }
 
+// DEPRECATED: Use NewGranularCustomCounter instead.
 func NewBPFCounter(desc *prometheus.Desc) BPFMetric {
-	return &bpfCounter{desc: desc}
+	return &bpfCounter{
+		metric: &granularCustomCounter[NilLabels]{
+			desc:        desc,
+			constrained: false,
+		},
+	}
 }
 
-func (c *bpfCounter) Desc() *prometheus.Desc {
-	return c.desc
+func (m *bpfCounter) Desc() *prometheus.Desc {
+	return m.metric.Desc()
 }
 
-func (c *bpfCounter) MustMetric(value float64, labelValues ...string) prometheus.Metric {
-	return prometheus.MustNewConstMetric(c.desc, prometheus.CounterValue, value, labelValues...)
+func (m *bpfCounter) MustMetric(value float64, labelValues ...string) prometheus.Metric {
+	return m.metric.MustMetric(value, &NilLabels{}, labelValues...)
 }
 
 type bpfGauge struct {
-	desc *prometheus.Desc
+	metric *granularCustomGauge[NilLabels]
 }
 
+// DEPRECATED: Use NewGranularCustomGauge instead.
 func NewBPFGauge(desc *prometheus.Desc) BPFMetric {
-	return &bpfGauge{desc: desc}
+	return &bpfGauge{
+		metric: &granularCustomGauge[NilLabels]{
+			desc:        desc,
+			constrained: false,
+		},
+	}
 }
 
-func (g *bpfGauge) Desc() *prometheus.Desc {
-	return g.desc
+func (m *bpfGauge) Desc() *prometheus.Desc {
+	return m.metric.Desc()
 }
 
-func (g *bpfGauge) MustMetric(value float64, labelValues ...string) prometheus.Metric {
-	return prometheus.MustNewConstMetric(g.desc, prometheus.GaugeValue, value, labelValues...)
+func (m *bpfGauge) MustMetric(value float64, labelValues ...string) prometheus.Metric {
+	return m.metric.MustMetric(value, &NilLabels{}, labelValues...)
 }

pkg/metrics/customcollector.go

@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type collectFunc func(chan<- prometheus.Metric)
+
+type customCollector[L FilteredLabels] struct {
+	metrics            []GranularCustomMetric[L]
+	collectFunc        collectFunc
+	collectForDocsFunc collectFunc
+}
+
+// NewCustomCollector creates a new customCollector.
+//
+// If collectForDocs is nil, the collector will use collect function for both
+// regular metrics server and generating documentation.
+func NewCustomCollector[L FilteredLabels](
+	metrics []GranularCustomMetric[L], collect collectFunc, collectForDocs collectFunc,
+) CollectorWithInit {
+	return &customCollector[L]{
+		metrics:            metrics,
+		collectFunc:        collect,
+		collectForDocsFunc: collectForDocs,
+	}
+}
+
+// Describe implements CollectorWithInit (prometheus.Collector).
+func (c *customCollector[L]) Describe(ch chan<- *prometheus.Desc) {
+	for _, m := range c.metrics {
+		ch <- m.Desc()
+	}
+}
+
+// Collect implements CollectorWithInit (prometheus.Collector).
+func (c *customCollector[L]) Collect(ch chan<- prometheus.Metric) {
+	if c.collectFunc != nil {
+		c.collectFunc(ch)
+	}
+}
+
+// IsConstrained implements CollectorWithInit.
+func (c *customCollector[L]) IsConstrained() bool {
+	for _, m := range c.metrics {
+		if !m.IsConstrained() {
+			return false
+		}
+	}
+	return true
+}
+
+// Init implements CollectorWithInit.
+func (c *customCollector[L]) Init() {
+	// since metrics are collected independently, there's nothing to initialize
+}
+
+// InitForDocs implements CollectorWithInit.
+func (c *customCollector[L]) InitForDocs() {
+	// override Collect method if there's a separate one for docs
+	if c.collectForDocsFunc != nil {
+		c.collectFunc = c.collectForDocsFunc
+	}
+}

pkg/metrics/custommetric.go

@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// GranularCustomMetric represents a metric collected independently of
+// prometheus package, for example in a BPF map. It's intended to be used in
+// a custom collector (see customcollector.go). The interface doesn't provide
+// any validation, so it's up to the collector implementer to guarantee the
+// metrics consistency.
+type GranularCustomMetric[L FilteredLabels] interface {
+	Desc() *prometheus.Desc
+	MustMetric(value float64, commonLvs *L, extraLvs ...string) prometheus.Metric
+	IsConstrained() bool
+}
+
+// getDesc is a helper function to retrieve the descriptor for a metric and
+// check if the metric is constrained.
+//
+// See getVariableLabels for the labels order.
+func getDesc[L FilteredLabels](opts *MetricOpts) (*prometheus.Desc, bool, error) {
+	labels, constrained, err := getVariableLabels[L](opts)
+	if err != nil {
+		return nil, false, err
+	}
+
+	desc := prometheus.NewDesc(
+		prometheus.BuildFQName(opts.Namespace, opts.Subsystem, opts.Name),
+		opts.Help,
+		labels,
+		opts.ConstLabels,
+	)
+	return desc, constrained, nil
+}
+
+// counter
+
+type granularCustomCounter[L FilteredLabels] struct {
+	desc        *prometheus.Desc
+	constrained bool
+}
+
+// NewGranularCustomCounter creates a new granularCustomCounter.
+func NewGranularCustomCounter[L FilteredLabels](opts MetricOpts) (GranularCustomMetric[L], error) {
+	desc, constrained, err := getDesc[L](&opts)
+	if err != nil {
+		return nil, err
+	}
+
+	return &granularCustomCounter[L]{
+		desc:        desc,
+		constrained: constrained,
+	}, nil
+}
+
+// MustNewGranularCustomCounter is a convenience function that wraps
+// NewGranularCustomCounter and panics on error.
+func MustNewGranularCustomCounter[L FilteredLabels](opts MetricOpts) GranularCustomMetric[L] {
+	m, err := NewGranularCustomCounter[L](opts)
+	if err != nil {
+		panic(err)
+	}
+	return m
+}
+
+// NewCustomCounter creates a new granularCustomCounter with no configurable labels.
+func NewCustomCounter(opts MetricOpts) (GranularCustomMetric[NilLabels], error) {
+	return NewGranularCustomCounter[NilLabels](opts)
+}
+
+// MustNewCustomCounter is a convenience function that wraps NewCustomCounter
+// and panics on error.
+func MustNewCustomCounter(opts MetricOpts) GranularCustomMetric[NilLabels] {
+	return MustNewGranularCustomCounter[NilLabels](opts)
+}
+
+// Desc implements GranularCustomMetric.
+func (m *granularCustomCounter[L]) Desc() *prometheus.Desc {
+	return m.desc
+}
+
+// MustMetric implements GranularCustomMetric.
+func (m *granularCustomCounter[L]) MustMetric(value float64, commonLvs *L, extraLvs ...string) prometheus.Metric {
+	lvs := append((*commonLvs).Values(), extraLvs...)
+	return prometheus.MustNewConstMetric(m.desc, prometheus.CounterValue, value, lvs...)
+}
+
+// IsConstrained implements GranularCustomMetric.
+func (m *granularCustomCounter[L]) IsConstrained() bool {
+	return m.constrained
+}
+
+// gauge
+
+type granularCustomGauge[L FilteredLabels] struct {
+	desc        *prometheus.Desc
+	constrained bool
+}
+
+// NewGranularCustomGauge creates a new granularCustomGauge.
+func NewGranularCustomGauge[L FilteredLabels](opts MetricOpts) (GranularCustomMetric[L], error) {
+	desc, constrained, err := getDesc[L](&opts)
+	if err != nil {
+		return nil, err
+	}
+
+	return &granularCustomGauge[L]{
+		desc:        desc,
+		constrained: constrained,
+	}, nil
+}
+
+// MustNewGranularCustomGauge is a convenience function that wraps
+// NewGranularCustomGauge and panics on error.
+func MustNewGranularCustomGauge[L FilteredLabels](opts MetricOpts) GranularCustomMetric[L] {
+	m, err := NewGranularCustomGauge[L](opts)
+	if err != nil {
+		panic(err)
+	}
+	return m
+}
+
+// NewCustomGauge creates a new granularCustomGauge with no configurable labels.
+func NewCustomGauge(opts MetricOpts) (GranularCustomMetric[NilLabels], error) {
+	return NewGranularCustomGauge[NilLabels](opts)
+}
+
+// MustNewCustomGauge is a convenience function that wraps NewCustomGauge
+// and panics on error.
+func MustNewCustomGauge(opts MetricOpts) GranularCustomMetric[NilLabels] {
+	return MustNewGranularCustomGauge[NilLabels](opts)
+}
+
+// Desc implements GranularCustomMetric.
+func (m *granularCustomGauge[L]) Desc() *prometheus.Desc {
+	return m.desc
+}
+
+// MustMetric implements GranularCustomMetric.
+func (m *granularCustomGauge[L]) MustMetric(value float64, commonLvs *L, extraLvs ...string) prometheus.Metric {
+	lvs := append((*commonLvs).Values(), extraLvs...)
+	return prometheus.MustNewConstMetric(m.desc, prometheus.GaugeValue, value, lvs...)
+}
+
+// IsConstrained implements GranularCustomMetric.
+func (m *granularCustomGauge[L]) IsConstrained() bool {
+	return m.constrained
+}

pkg/metrics/filteredlabels.go

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+
+package metrics
+
+import (
+	"github.com/cilium/tetragon/pkg/metrics/consts"
+)
+
+type FilteredLabels interface {
+	Keys() []string
+	Values() []string
+}
+
+// FilteredLabelsWithExamples extends FilteredLabels with a method returning
+// example label values, intended to be used when generating documentation.
+type FilteredLabelsWithExamples interface {
+	FilteredLabels
+	ExampleValues() []string
+}
+
+type NilLabels struct{}
+
+func (l NilLabels) Keys() []string { return []string{} }
+
+func (l NilLabels) Values() []string { return []string{} }
+
+func (l NilLabels) ExampleValues() []string { return []string{} }
+
+type ProcessLabels struct {
+	Namespace string
+	Workload  string
+	Pod       string
+	Binary    string
+}
+
+func NewProcessLabels(namespace, workload, pod, binary string) *ProcessLabels {
+	return &ProcessLabels{
+		Namespace: namespace,
+		Workload:  workload,
+		Pod:       pod,
+		Binary:    binary,
+	}
+}
+
+func (l ProcessLabels) Keys() []string {
+	return []string{"namespace", "workload", "pod", "binary"}
+}
+
+func (l ProcessLabels) Values() []string {
+	return []string{l.Namespace, l.Workload, l.Pod, l.Binary}
+}
+
+func (l ProcessLabels) ExampleValues() []string {
+	return []string{consts.ExampleNamespace, consts.ExampleWorkload, consts.ExamplePod, consts.ExampleBinary}
+}