Observability

The observability package provides instrumentation for monitoring and tracing Gofasta applications. It integrates Prometheus for metrics collection and OpenTelemetry for distributed tracing, using standard net/http middleware.

Import


import "github.com/gofastadev/gofasta/pkg/observability"

Metrics

Built-in Metrics

The package automatically registers the following Prometheus metrics:

Metric	Type	Labels	Description
`http_requests_total`	Counter	method, path, status	Total number of HTTP requests
`http_request_duration_seconds`	Histogram	method, path	HTTP request duration in seconds
`http_requests_in_flight`	Gauge	—	Number of HTTP requests currently being processed

Key Functions

Function	Signature	Description
`MetricsMiddleware`	`func MetricsMiddleware(next http.Handler) http.Handler`	Records HTTP request metrics (count, duration, in-flight)
`MetricsHandler`	`func MetricsHandler() http.Handler`	Returns the Prometheus metrics HTTP handler
`InitTracer`	`func InitTracer(serviceName string) func()`	Initializes the OpenTelemetry tracer provider and returns a shutdown function
`TracingMiddleware`	`func TracingMiddleware(serviceName string) func(http.Handler) http.Handler`	Creates spans for HTTP requests and propagates trace context

Usage

Setting Up Metrics


// Expose the Prometheus metrics endpoint
mux.Handle("GET /metrics", observability.MetricsHandler())
 
// Wrap your handler with metrics middleware
handler := observability.MetricsMiddleware(mux)

The MetricsMiddleware is a plain func(http.Handler) http.Handler — it wraps the handler directly without requiring a config struct.

Setting Up Tracing


shutdown := observability.InitTracer("my-service")
defer shutdown()
 
// Add tracing middleware to create spans for HTTP requests
handler := observability.TracingMiddleware("my-service")(mux)

The tracer uses OpenTelemetry with AlwaysSample by default. In production, configure an exporter (OTLP, Jaeger, Zipkin) via the OpenTelemetry SDK.

Combining Metrics and Tracing


shutdown := observability.InitTracer("my-service")
defer shutdown()
 
mux.Handle("GET /metrics", observability.MetricsHandler())
 
// Apply both middleware
handler := observability.MetricsMiddleware(
    observability.TracingMiddleware("my-service")(mux),
)
 
http.ListenAndServe(":8080", handler)

Configuration via config.yaml


observability:
  metrics_enabled: true
  tracing_enabled: true
  metrics_path: /metrics
  service_name: my-service

Environment variables use the GOFASTA_ prefix (e.g., GOFASTA_OBSERVABILITY_METRICS_ENABLED, GOFASTA_OBSERVABILITY_SERVICE_NAME).

Logger — Structured logging complements metrics and traces
Health — Health endpoints alongside metrics
Middleware — Apply observability middleware to routes
Resilience — Retries and circuit breakers expose metrics here
Feature Flags — Flag evaluation surfaces in trace span attributes