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docs(keycast): document health probe ordering and shutdown semantics #218

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docs(keycast): document health probe ordering and shutdown semantics #218

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11 changes: 11 additions & 0 deletions keycast/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,9 @@ struct ReadinessState {
shutting_down: Arc<AtomicBool>,
}

/// Maps probe state to HTTP status. Shutdown is checked before DB readiness so
/// during graceful shutdown we skip the DB query in [`readyz`] yet still return
/// 503 with body `"Shutting down"` (not `"Database unavailable"`).
fn readiness_response(is_shutting_down: bool, database_ready: bool) -> (StatusCode, &'static str) {
if is_shutting_down {
(StatusCode::SERVICE_UNAVAILABLE, "Shutting down")
Expand Down Expand Up @@ -86,13 +89,19 @@ async fn livez(state: Arc<LivenessState>) -> impl IntoResponse {
}
}

/// Startup probe: always 200 when reachable. Safe because the listener binds only
/// after `Database::new().await` in startup succeeds; this handler does not
/// re-check the DB. Schema must already be migrated for the revision (e.g. `--migrate`
/// / deploy job—migrations are not run inside `Database::new`).
async fn startupz() -> impl IntoResponse {
(StatusCode::OK, "OK")
}

async fn readyz(state: Arc<ReadinessState>) -> impl IntoResponse {
let is_shutting_down = state.shutting_down.load(Ordering::Relaxed);
let database_ready = if is_shutting_down {
// Intentionally skip DB work while shutting down; [`readiness_response`]
// still reports 503 `"Shutting down"` via the shutdown branch first.
false
} else {
// Bound the DB check so a stalled connection or exhausted pool fails
Expand Down Expand Up @@ -832,6 +841,8 @@ async fn async_main(worker_threads: usize) -> Result<(), Box<dyn std::error::Err
.route("/health", get(health_check))
.route("/livez", get(move || livez(livez_state.clone())))
.route("/healthz/startup", get(startupz))
// Cloud Run does not use K8s-style readiness to stop routing to an instance;
// this endpoint is mainly for smoke tests (e.g. Cloud Build) and Kubernetes.
.route("/healthz/ready", get(move || readyz(readyz_state.clone())))
// NIP-05 discovery at root level
.route(
Expand Down
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