Prometheus

Prometheus records a request counter and total duration for each route, method, and status, and serves them in Prometheus text format. It needs no dependencies. For histograms or the official client library, register promhttp.Handler() with HandleHTTP instead.

metrics := middleware.NewPrometheusMetrics()

app.Use(middleware.Prometheus(metrics))
app.Get("/metrics", middleware.PrometheusHandler(metrics))

The handler writes Prometheus text format:

zinc_http_requests_total
zinc_http_request_duration_seconds_sum
zinc_http_request_duration_seconds_count

Labels include:

• method
• route
• status

Matched requests use registered route patterns, such as /users/{id}. Unmatched requests use unmatched; nonstandard methods use OTHER. Random request paths and methods therefore do not create new series.

Each Prometheus() construction creates an isolated registry. PrometheusHandler() without an argument uses the registry attached by middleware on that request, including when collection is skipped. Without middleware or an explicit registry, the handler returns 503. Reusing one middleware instance intentionally shares its registry; supply explicit registries when composing multiple collectors.

NewPrometheusMetrics(maxSeries) optionally sets a series cap (default 10,000). New series beyond the cap are dropped, counted by zinc_http_metrics_dropped_total. Existing series continue updating. Direct calls to Observe should use application-controlled labels.