Metrics Invoker

The metrics invoker records latency and success/failure counts for every handler invocation.

Configuration

invoker.NewMetrics(provider) // MetricProvider implementation
invoker.NewMetrics(nil)      // Uses NoopProvider (silent)

MetricProvider Interface

type MetricProvider interface {
    IncCounter(name string, n int64, labels Labels)
    ObserveHistogram(name string, value float64, labels Labels)
    SetGauge(name string, value float64, labels Labels)
}

Where Labels is map[string]string.

Built-in Providers

• NoopProvider: Discards all metrics (default when nil is passed)
• Prometheus Provider: prometheus.NewProvider(namespace) (see Prometheus)

Collected Metrics

Metric	Type	Labels	Description
eventbus_invoker_latency_seconds	Histogram	event, handler, result	Handler execution latency
eventbus_invoker_calls_total	Counter	event, handler, result	Total handler invocations

The result label is "ok" on success and "err" on failure.

Position in Chain

The metrics invoker should be placed early in the chain (after tracing) to capture the full execution time including retries, circuit breaker decisions, etc.