Metrics

rust-web-server exposes two tiers of Prometheus-compatible metrics. Server-wide counters are always active at the server-core level with no configuration. Per-route counters and latency histograms are opt-in via MetricsLayer middleware. All metrics are served at GET /metrics in the standard Prometheus text format.

Server-wide counters

These atomics are updated by Server::process() and the connection dispatch loop automatically. No middleware registration is required.

Symbol	Type	Description
REQUESTS_TOTAL	counter	Total HTTP requests handled across all connections and protocols
ERRORS_TOTAL	counter	Requests where app.execute() returned Err
ACTIVE_CONNECTIONS	gauge	Number of currently open TCP/QUIC connections
SERVER_READY	AtomicBool	true after server setup; false during shutdown; drives /readyz

Helper functions

use rust_web_server::metrics;

metrics::record_request();   // increments REQUESTS_TOTAL
metrics::record_error();     // increments ERRORS_TOTAL
metrics::connection_open();  // increments ACTIVE_CONNECTIONS
metrics::connection_close(); // decrements ACTIVE_CONNECTIONS

These functions are called by the server core, but you can also call them from custom instrumentation code.

GET /metrics endpoint

The built-in endpoint returns all metrics in Prometheus text format. No setup is needed — it is registered automatically by App::new().

# HELP rws_requests_total Total HTTP requests handled
# TYPE rws_requests_total counter
rws_requests_total 12483

# HELP rws_errors_total HTTP requests that returned an application error
# TYPE rws_errors_total counter
rws_errors_total 3

# HELP rws_active_connections Currently open connections
# TYPE rws_active_connections gauge
rws_active_connections 7

When MetricsLayer is active, per-route metrics are appended to the same response body.

Per-route metrics with MetricsLayer

Wrap your application once at startup to enable per-route request counts and latency histograms:

use rust_web_server::app::App;
use rust_web_server::core::New;
use rust_web_server::metrics::MetricsLayer;

let app = App::new().wrap(MetricsLayer);

MetricsLayer records two metric families per (method, path) pair after each request completes.

rws_route_requests_total

A counter labelled by method, path, and HTTP status code.

# HELP rws_route_requests_total Total requests handled per route
# TYPE rws_route_requests_total counter
rws_route_requests_total{method="GET",path="/api/users",status="200"} 9401
rws_route_requests_total{method="GET",path="/api/users",status="404"} 12
rws_route_requests_total{method="POST",path="/api/users",status="201"} 530

Query strings are stripped from the path label automatically (/users?page=2 → /users).

rws_route_duration_seconds

A cumulative histogram labelled by method and path, with 11 predefined buckets matching the default Prometheus/Go client boundaries:

0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0 (seconds)

# HELP rws_route_duration_seconds Request duration in seconds per route
# TYPE rws_route_duration_seconds histogram
rws_route_duration_seconds_bucket{method="GET",path="/api/users",le="0.005"} 8200
rws_route_duration_seconds_bucket{method="GET",path="/api/users",le="0.01"} 9100
...
rws_route_duration_seconds_bucket{method="GET",path="/api/users",le="+Inf"} 9413
rws_route_duration_seconds_sum{method="GET",path="/api/users"} 47.231000000
rws_route_duration_seconds_count{method="GET",path="/api/users"} 9413

SERVER_READY and /readyz

The built-in GET /readyz controller returns 200 OK when SERVER_READY is true and 503 Service Unavailable when it is false. The flag is set to true after Server::setup() completes and back to false when a shutdown signal is received, so Kubernetes stops routing traffic before the pod exits.

use rust_web_server::metrics::SERVER_READY;
use std::sync::atomic::Ordering;

// Check readiness programmatically.
let ready = SERVER_READY.load(Ordering::Relaxed);

Scraping with Prometheus

prometheus.yml

scrape_configs:
  - job_name: rws
    static_configs:
      - targets: ["localhost:7878"]
    metrics_path: /metrics