Tutorial 23: Process Telemetry & Prometheus Exporter 📡

Monitor process uptime, RSS memory, CPU, Tokio scheduler-yield latency, and active tasks using Rullst Radar (rullst::radar) and Prometheus (GET /metrics).

🛠️ Step 1: Mount Prometheus Exporter

In src/main.rs:

use rullst::radar::radar_metrics_router;
use rullst::{Router, Server, ServerError};

#[rullst::runtime::main]
async fn main() -> Result<(), ServerError> {
    let app = Router::new().merge_axum(radar_metrics_router()); // Exposes GET /metrics

    Server::new(app).run(3000).await
}

In a generated project, add .merge_axum(rullst::radar::radar_metrics_router()) to the router that main passes to Server::new, then run cargo rullst dev and open http://localhost:3000/metrics.

📊 Step 2: Prometheus Metrics Scrape Output

Query GET /metrics:

# HELP rullst_uptime_seconds Process uptime in seconds.
# TYPE rullst_uptime_seconds counter
rullst_uptime_seconds 120

# HELP rullst_memory_rss_bytes Process RSS memory consumption in bytes.
# TYPE rullst_memory_rss_bytes gauge
rullst_memory_rss_bytes 24536678

# HELP rullst_cpu_usage_percent Process CPU utilization percentage.
# TYPE rullst_cpu_usage_percent gauge
rullst_cpu_usage_percent 1.25

# HELP rullst_tokio_active_tasks Total active Tokio tasks count.
# TYPE rullst_tokio_active_tasks gauge
rullst_tokio_active_tasks 4

# HELP rullst_tokio_latency_microseconds Observed Tokio scheduler yield latency in microseconds.
# TYPE rullst_tokio_latency_microseconds gauge
rullst_tokio_latency_microseconds 42

The CPU gauge needs an earlier sample in the same process, so the first collection omits it.

In a debug build the generated starters also start Studio, whose Radar page shows the same process measurements: http://127.0.0.1:5555/studio/radar.

/metrics is not authenticated by radar_metrics_router(). Restrict it with a private network, service-mesh policy, or reviewed authentication middleware; process and runtime measurements can disclose operational information.

💡 Key Takeaways

• The response is a point-in-time local snapshot and allocates its text body.
• Linux and Windows expose supported process RSS/CPU probes. Tokio task data is available only inside a Tokio runtime; unsupported probes are omitted.
• The scheduler-yield observation is not a universal request-latency target.