Edouard Vanbelle
98 lines
4.1 KiB
Rust
98 lines
4.1 KiB
Rust
//! Prometheus `/metrics` exporter — opt-in, isolated listener.
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//!
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//! Enabled iff `OXICLOUD_METRICS_LISTEN` is set (see
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//! [`crate::common::config::AppConfig::metrics_listen`]). When unset,
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//! no recorder is installed and every `metrics::counter!(…)` call
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//! across the codebase compiles to a no-op — no runtime cost, no
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//! endpoint bound. When set, this module:
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//!
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//! 1. Installs the process-global Prometheus recorder (once — panics
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//! if called twice, so [`spawn`] MUST be a single-call site).
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//! 2. Binds a fresh `axum` `Router` on the configured address exposing
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//! only `GET /metrics`. Deliberately **not merged** into the main
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//! API router — operators bind to loopback / a private interface
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//! (typical: `127.0.0.1:9090` for a node_exporter-adjacent scrape)
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//! without any auth, CSRF, or DPoP layer in front. Public exposure
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//! is an operator choice via the bind address, not an app default.
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//! 3. Spawns the listener on a detached tokio task — the metrics
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//! endpoint's lifetime tracks the runtime, and a listener error
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//! logs but doesn't take the main server down.
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//!
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//! Counter naming follows Prometheus conventions:
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//! `oxicloud_<subsystem>_<verb>_total{label=…}`. Emission is
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//! **duplicated** with existing audit `tracing::info!(target: "audit", …)`
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//! lines — logs stay authoritative for incident forensics; counters
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//! are for rate / rollup dashboards. Never remove one when adding the
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//! other.
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//!
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//! Starter counter surface (extend as needed):
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//! * `oxicloud_dpop_verify_failed_total{reason}`
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//! * `oxicloud_dpop_proof_missing_total`
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//! * `oxicloud_dpop_header_missing_on_bound_session_total`
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//! * `oxicloud_dpop_replay_detected_total`
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//! * `oxicloud_dpop_nonce_challenges_issued_total`
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use axum::{Router, extract::State, http::header, response::IntoResponse, routing::get};
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use metrics_exporter_prometheus::{PrometheusBuilder, PrometheusHandle};
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use std::net::SocketAddr;
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/// Error type returned by [`spawn`]. Uses the same `Box<dyn Error>`
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/// shape `main` already threads for setup failures — one less crate
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/// dep (`anyhow`) and no coupling to a specific error framework.
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pub type BoxError = Box<dyn std::error::Error + Send + Sync>;
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/// Install the Prometheus recorder and spawn the `/metrics` listener.
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///
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/// Idempotent-unsafe: MUST be called at most once per process (the
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/// recorder is a process-global singleton). Caller (main.rs) checks
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/// `config.metrics_listen.is_some()` — no runtime guard here.
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///
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/// Returns immediately after `bind` succeeds; the listener runs on a
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/// detached tokio task. A bind failure returns the error so main can
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/// decide whether to abort (recommended) or continue without metrics.
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pub async fn spawn(bind: SocketAddr) -> Result<(), BoxError> {
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let handle: PrometheusHandle =
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PrometheusBuilder::new()
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.install_recorder()
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.map_err(|err| -> BoxError {
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format!("failed to install Prometheus recorder: {err}").into()
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})?;
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let app = Router::new()
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.route("/metrics", get(scrape))
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.with_state(handle);
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let listener = tokio::net::TcpListener::bind(bind)
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.await
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.map_err(|err| -> BoxError {
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format!("failed to bind metrics listener on {bind}: {err}").into()
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})?;
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let actual = listener.local_addr()?;
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tracing::info!(
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target: "oxicloud::metrics",
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"📊 Prometheus /metrics listening on http://{actual}/metrics",
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);
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tokio::spawn(async move {
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if let Err(err) = axum::serve(listener, app).await {
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tracing::error!(
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target: "oxicloud::metrics",
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"metrics listener terminated with error: {err}",
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);
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}
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});
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Ok(())
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}
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/// Render the current Prometheus text-format snapshot. Content-type
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/// per spec: `text/plain; version=0.0.4`; scrapers parse strictly.
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async fn scrape(State(handle): State<PrometheusHandle>) -> impl IntoResponse {
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(
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[(
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header::CONTENT_TYPE,
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"text/plain; version=0.0.4; charset=utf-8",
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)],
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handle.render(),
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)
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}
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