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Allow for custom labels on prometheus metrics #393

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Allow for custom labels on prometheus metrics #393

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44cdd43
feat: allow for custom labels on prometheus metrics
matdurand Sep 14, 2023
cb73514
fix: move to a config struct pattern
matdurand Sep 21, 2023
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39 changes: 29 additions & 10 deletions components/metrics/builder.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,12 +7,27 @@ import (
"github.com/prometheus/client_golang/prometheus"
)

func NewPrometheusMetricsBuilder(prometheusRegistry prometheus.Registerer, namespace string, subsystem string) PrometheusMetricsBuilder {
return PrometheusMetricsBuilder{
Namespace: namespace,
Subsystem: subsystem,
type PrometheusMetricsBuilderConfig struct {
Namespace string
Subsystem string
AdditionalLabels []MetricLabel
}

func NewPrometheusMetricsBuilderWithConfig(prometheusRegistry prometheus.Registerer, config PrometheusMetricsBuilderConfig) PrometheusMetricsBuilder {
builder := PrometheusMetricsBuilder{
Namespace: config.Namespace,
Subsystem: config.Subsystem,
PrometheusRegistry: prometheusRegistry,
additionalLabels: config.AdditionalLabels,
}
return builder
}

func NewPrometheusMetricsBuilder(prometheusRegistry prometheus.Registerer, namespace string, subsystem string) PrometheusMetricsBuilder {
return NewPrometheusMetricsBuilderWithConfig(prometheusRegistry, PrometheusMetricsBuilderConfig{
Namespace: namespace,
Subsystem: subsystem,
})
}

// PrometheusMetricsBuilder provides methods to decorate publishers, subscribers and handlers.
Expand All @@ -22,6 +37,8 @@ type PrometheusMetricsBuilder struct {

Namespace string
Subsystem string

additionalLabels []MetricLabel
}

// AddPrometheusRouterMetrics is a convenience function that acts on the message router to add the metrics middleware
Expand All @@ -36,8 +53,9 @@ func (b PrometheusMetricsBuilder) AddPrometheusRouterMetrics(r *message.Router)
func (b PrometheusMetricsBuilder) DecoratePublisher(pub message.Publisher) (message.Publisher, error) {
var err error
d := PublisherPrometheusMetricsDecorator{
pub: pub,
publisherName: internal.StructName(pub),
pub: pub,
publisherName: internal.StructName(pub),
additionalLabels: b.additionalLabels,
}

d.publishTimeSeconds, err = b.registerHistogramVec(prometheus.NewHistogramVec(
Expand All @@ -47,7 +65,7 @@ func (b PrometheusMetricsBuilder) DecoratePublisher(pub message.Publisher) (mess
Name: "publish_time_seconds",
Help: "The time that a publishing attempt (success or not) took in seconds",
},
publisherLabelKeys,
toLabelsSlice(publisherLabelKeys, b.additionalLabels),
))
if err != nil {
return nil, errors.Wrap(err, "could not register publish time metric")
Expand All @@ -59,8 +77,9 @@ func (b PrometheusMetricsBuilder) DecoratePublisher(pub message.Publisher) (mess
func (b PrometheusMetricsBuilder) DecorateSubscriber(sub message.Subscriber) (message.Subscriber, error) {
var err error
d := &SubscriberPrometheusMetricsDecorator{
closing: make(chan struct{}),
subscriberName: internal.StructName(sub),
closing: make(chan struct{}),
subscriberName: internal.StructName(sub),
additionalLabels: b.additionalLabels,
}

d.subscriberMessagesReceivedTotal, err = b.registerCounterVec(prometheus.NewCounterVec(
Expand All @@ -70,7 +89,7 @@ func (b PrometheusMetricsBuilder) DecorateSubscriber(sub message.Subscriber) (me
Name: "subscriber_messages_received_total",
Help: "The total number of messages received by the subscriber",
},
append(subscriberLabelKeys, labelAcked),
toLabelsSlice(append(subscriberLabelKeys, labelAcked), b.additionalLabels),
))
if err != nil {
return nil, errors.Wrap(err, "could not register time to ack metric")
Expand Down
10 changes: 8 additions & 2 deletions components/metrics/handler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ var (
// HandlerPrometheusMetricsMiddleware is a middleware that captures Prometheus metrics.
type HandlerPrometheusMetricsMiddleware struct {
handlerExecutionTimeSeconds *prometheus.HistogramVec
additionalLabels []MetricLabel
}

// Middleware returns the middleware ready to be used with watermill's Router.
Expand All @@ -45,6 +46,9 @@ func (m HandlerPrometheusMetricsMiddleware) Middleware(h message.HandlerFunc) me
labels := prometheus.Labels{
labelKeyHandlerName: message.HandlerNameFromCtx(ctx),
}
for _, lb := range m.additionalLabels {
labels[lb.Label] = lb.ComputeFn(ctx)
}

defer func() {
if err != nil {
Expand All @@ -62,7 +66,9 @@ func (m HandlerPrometheusMetricsMiddleware) Middleware(h message.HandlerFunc) me
// NewRouterMiddleware returns new middleware.
func (b PrometheusMetricsBuilder) NewRouterMiddleware() HandlerPrometheusMetricsMiddleware {
var err error
m := HandlerPrometheusMetricsMiddleware{}
m := HandlerPrometheusMetricsMiddleware{
additionalLabels: b.additionalLabels,
}

m.handlerExecutionTimeSeconds, err = b.registerHistogramVec(prometheus.NewHistogramVec(
prometheus.HistogramOpts{
Expand All @@ -72,7 +78,7 @@ func (b PrometheusMetricsBuilder) NewRouterMiddleware() HandlerPrometheusMetrics
Help: "The total time elapsed while executing the handler function in seconds",
Buckets: handlerExecutionTimeBuckets,
},
handlerLabelKeys,
toLabelsSlice(handlerLabelKeys, b.additionalLabels),
))
if err != nil {
panic(errors.Wrap(err, "could not register handler execution time metric"))
Expand Down
27 changes: 27 additions & 0 deletions components/metrics/labels.go
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Original file line number Diff line number Diff line change
Expand Up @@ -46,3 +46,30 @@ func labelsFromCtx(ctx context.Context, labels ...string) prometheus.Labels {

return ctxLabels
}

type LabelComputeFn func(msgCtx context.Context) string
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We might want to reflect on that signature. Is it enough to use only the context to get a label's value? Should we also pass the message pointer? For my use case, the additional labels are static, so I basically do this

        metrics.MetricLabel{
		Label: "service",
		ComputeFn: func(ctx context.Context) string {
			return "my_service"
		},
	},

but there might be a use case for getting something from the message itself as a label value.


type MetricLabel struct {
Label string
ComputeFn LabelComputeFn
}

func toLabelsSlice(baseLabels []string, customs []MetricLabel) []string {
labels := make([]string, len(baseLabels), len(baseLabels)+len(customs))
copy(labels, baseLabels)
for _, label := range customs {
//Check if the additional label is already in the base labels. We cannot have duplicate labels
//If it's in the base, just skip it as the compute function is going to overwrite the default value
contains := false
for _, baseLabel := range baseLabels {
if baseLabel == label.Label {
contains = true
break
}
}
if !contains {
labels = append(labels, label.Label)
}
}
return labels
}
4 changes: 4 additions & 0 deletions components/metrics/publisher.go
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Expand Up @@ -20,6 +20,7 @@ type PublisherPrometheusMetricsDecorator struct {
pub message.Publisher
publisherName string
publishTimeSeconds *prometheus.HistogramVec
additionalLabels []MetricLabel
}

// Publish updates the relevant publisher metrics and calls the wrapped publisher's Publish.
Expand All @@ -37,6 +38,9 @@ func (m PublisherPrometheusMetricsDecorator) Publish(topic string, messages ...*
if labels[labelKeyHandlerName] == "" {
labels[labelKeyHandlerName] = labelValueNoHandler
}
for _, lb := range m.additionalLabels {
labels[lb.Label] = lb.ComputeFn(ctx)
}
start := time.Now()

defer func() {
Expand Down
4 changes: 4 additions & 0 deletions components/metrics/subscriber.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ type SubscriberPrometheusMetricsDecorator struct {
subscriberName string
subscriberMessagesReceivedTotal *prometheus.CounterVec
closing chan struct{}
additionalLabels []MetricLabel
}

func (s SubscriberPrometheusMetricsDecorator) recordMetrics(msg *message.Message) {
Expand All @@ -33,6 +34,9 @@ func (s SubscriberPrometheusMetricsDecorator) recordMetrics(msg *message.Message
if labels[labelKeyHandlerName] == "" {
labels[labelKeyHandlerName] = labelValueNoHandler
}
for _, lb := range s.additionalLabels {
labels[lb.Label] = lb.ComputeFn(ctx)
}

go func() {
if subscribeAlreadyObserved(ctx) {
Expand Down