OpenTelemetry Hook

Requirements

• open-feature/go-sdk >= v1.3.0

Usage

Metrics hook

This hook performs metric collection by tapping into various hook stages. Given below are the metrics are extracted by this hook,

• feature_flag.evaluation_requests_total
• feature_flag.evaluation_success_total
• feature_flag.evaluation_error_total
• feature_flag.evaluation_active_count

There are two ways to create hooks:

Using Global MeterProvider

Global provider should be set somewhere using otel.SetMeterProvider before calling this constructor.

// Derive metric hook from reader
metricsHook, err := hooks.NewMetricsHook()
if err != nil {
    return err
}

// Register OpenFeature API level hooks
openfeature.AddHooks(metricsHook)

Passing MeterProvider to Constructor

// provider must be configured and provided to constructor based on application configurations
var provider *metric.MeterProvider

// Derive metric hook from reader
metricsHook, err := hooks.NewMetricsHookForProvider(provider)
if err != nil {
    return err
}

// Register OpenFeature API level hooks
openfeature.AddHooks(metricsHook)

Options

WithMetricsAttributeSetter

This constructor options allows to provide a custom callback to extract dimensions from FlagMetadata. These attributes are added at the After stage of the hook.

NewMetricsHookForProvider(provider,
    WithMetricsAttributeSetter(
    func(metadata openfeature.FlagMetadata) []attribute.KeyValue {
		// custom attribute extraction logic

        return attributes
    }))

WithFlagMetadataDimensions

This constructor option allows to configure dimension descriptions to be extracted from openfeature.FlagMetadata. If present, these dimension will be added to the feature_flag.evaluation_success_total metric. Missing metadata keys will be ignored by the implementation.

NewMetricsHook(MeterProvider,
    WithFlagMetadataDimensions(
        DimensionDescription{
            Key:  "scope",
            Type: String,
        }))

Traces hook

The traces hook taps into the after and error methods of the hook lifecycle to write events and attributesto an existing span. A context.Context containing a span must be passed to the client evaluation method, otherwise the hook will be no-op.

// Register traces hook
openfeature.AddHooks(hooks.NewTracesHook())
client := openfeature.NewClient("methodA")

// Initialize otel span
spanCtx, span := tracer.Start(context.Background(), "myBoolFlag")
client.BooleanValueDetails(spanCtx, "myBoolFlag", false, openfeature.EvaluationContext{})

...

span.End()

Options

WithErrorStatusEnabled

Enable setting span status to Error in case of an error. Default behavior is disabled, span status is unset for errors.

WithTracesAttributeSetter

This constructor options allows to provide a custom callback to extract dimensions from FlagMetadata. These attributes are added at the After stage of the hook.

NewTracesHook(WithMetricsAttributeSetter(
    func(metadata openfeature.FlagMetadata) []attribute.KeyValue {
		// custom attribute extraction logic

        return attributes
    }))