feat: optional UDS listener + health endpoints for Kubernetes deployment

crates/sprout-db/src/lib.rs

@@ -925,6 +925,11 @@ impl Db {
         partition::ensure_future_partitions(&self.pool, months_ahead).await
     }
 
+    /// Returns `true` if the database is reachable (used by readiness probes).
+    pub async fn ping(&self) -> bool {
+        sqlx::query("SELECT 1").execute(&self.pool).await.is_ok()
+    }
+
     // ── Workflows ─────────────────────────────────────────────────────────────
 
     /// Creates a new workflow definition and returns its UUID.

crates/sprout-relay/src/config.rs

@@ -45,6 +45,9 @@ pub struct Config {
     /// Optional hex-encoded private key for the relay's signing keypair.
     /// If absent, a fresh keypair is generated at startup.
     pub relay_private_key: Option<String>,
+    /// Optional Unix Domain Socket path. When set, the relay also listens on this
+    /// UDS for traffic (e.g. service mesh sidecar). Health probes still use TCP.
+    pub uds_path: Option<String>,
 }
 
 impl Config {
@@ -118,6 +121,11 @@ impl Config {
 
         let relay_private_key = std::env::var("SPROUT_RELAY_PRIVATE_KEY").ok();
 
+        let uds_path = std::env::var("SPROUT_UDS_PATH")
+            .ok()
+            .map(|s| s.trim().to_string())
+            .filter(|s| !s.is_empty());
+
         Ok(Self {
             bind_addr,
             database_url,
@@ -132,6 +140,7 @@ impl Config {
             require_auth_token,
             cors_origins,
             relay_private_key,
+            uds_path,
         })
     }
 }

crates/sprout-relay/src/main.rs

@@ -61,6 +61,7 @@ async fn main() -> anyhow::Result<()> {
         cfg.create_pool(Some(deadpool_redis::Runtime::Tokio1))
             .map_err(|e| anyhow::anyhow!("Redis pool creation failed: {e}"))?
     };
+    let redis_health_pool = redis_pool.clone(); // cheap Arc clone — shared with readiness handler
     let pubsub = Arc::new(
         PubSubManager::new(&config.redis_url, redis_pool)
             .await
@@ -101,6 +102,7 @@ async fn main() -> anyhow::Result<()> {
     let state = Arc::new(AppState::new(
         config.clone(),
         db,
+        redis_health_pool,
         audit,
         pubsub,
         auth,
@@ -184,14 +186,59 @@ async fn main() -> anyhow::Result<()> {
 
     let router = build_router(Arc::clone(&state));
 
-    let listener = tokio::net::TcpListener::bind(&config.bind_addr)
+    serve_dual(router, &config).await
+}
+
+/// Bind TCP (always) and optionally UDS, then run both concurrently.
+/// If either listener exits, the function returns and the process exits.
+async fn serve_dual(router: axum::Router, config: &Config) -> anyhow::Result<()> {
+    let tcp_listener = tokio::net::TcpListener::bind(&config.bind_addr)
         .await
         .map_err(|e| anyhow::anyhow!("Failed to bind {}: {e}", config.bind_addr))?;
+    info!(addr = %config.bind_addr, "sprout-relay TCP listening");
+
+    #[cfg(unix)]
+    if let Some(ref uds_path) = config.uds_path {
+        // Only remove stale socket files — refuse to delete non-socket paths.
+        use std::os::unix::fs::FileTypeExt as _;
+        match std::fs::symlink_metadata(uds_path) {
+            Ok(meta) if meta.file_type().is_socket() => {
+                let _ = std::fs::remove_file(uds_path);
+            }
+            Ok(_) => {
+                return Err(anyhow::anyhow!(
+                    "SPROUT_UDS_PATH {uds_path} exists but is not a socket — refusing to delete"
+                ));
+            }
+            Err(_) => {} // Path doesn't exist — fine, we'll create it
+        }
+        let uds_listener = tokio::net::UnixListener::bind(uds_path)
+            .map_err(|e| anyhow::anyhow!("Failed to bind UDS {uds_path}: {e}"))?;
+        info!(path = %uds_path, "sprout-relay UDS listening");
+
+        let router_uds = router.clone();
+        tokio::select! {
+            r = axum::serve(
+                tcp_listener,
+                router.into_make_service_with_connect_info::<std::net::SocketAddr>(),
+            ) => r.map_err(|e| anyhow::anyhow!("TCP server error: {e}")),
+            r = axum::serve(uds_listener, router_uds.into_make_service()) =>
+                r.map_err(|e| anyhow::anyhow!("UDS server error: {e}")),
+        }?;
+        return Ok(());
+    }
 
-    info!(addr = %config.bind_addr, "sprout-relay listening");
+    #[cfg(not(unix))]
+    if config.uds_path.is_some() {
+        tracing::warn!(
+            "SPROUT_UDS_PATH is set but UDS is not supported on this platform — \
+             falling back to TCP only"
+        );
+    }
 
+    // TCP-only path (non-unix, or unix without uds_path set).
     axum::serve(
-        listener,
+        tcp_listener,
         router.into_make_service_with_connect_info::<std::net::SocketAddr>(),
     )
     .await

crates/sprout-relay/src/router.rs

@@ -9,6 +9,7 @@ use axum::{
     routing::{delete, get, post, put},
     Router,
 };
+use serde_json::json;
 use tower_http::cors::{AllowOrigin, CorsLayer};
 use tower_http::limit::RequestBodyLimitLayer;
 use tower_http::trace::TraceLayer;
@@ -26,6 +27,8 @@ pub fn build_router(state: Arc<AppState>) -> Router {
         .route("/info", get(relay_info_handler))
         .route("/.well-known/nostr.json", get(api::nip05::nostr_nip05))
         .route("/health", get(health_handler))
+        .route("/_liveness", get(liveness_handler))
+        .route("/_readiness", get(readiness_handler))
         // Token self-service routes
         .route(
             "/api/tokens",
@@ -153,12 +156,23 @@ pub fn build_router(state: Arc<AppState>) -> Router {
 ///
 /// Uses `axum::extract::Request` to manually attempt WS upgrade, so non-WS
 /// requests aren't rejected by the extractor.
+///
+/// `ConnectInfo` is read from request extensions rather than as an extractor —
+/// UDS connections have no `SocketAddr`, so the extractor would panic.
+/// TCP connections populate it via `into_make_service_with_connect_info`; UDS
+/// connections fall back to `0.0.0.0:0`.
 async fn nip11_or_ws_handler(
     State(state): State<Arc<AppState>>,
-    ConnectInfo(addr): ConnectInfo<std::net::SocketAddr>,
     headers: HeaderMap,
     req: axum::extract::Request,
 ) -> impl IntoResponse {
+    // Read peer address from extensions (set by TCP serve; absent for UDS).
+    let addr = req
+        .extensions()
+        .get::<ConnectInfo<std::net::SocketAddr>>()
+        .map(|ci| ci.0)
+        .unwrap_or_else(|| std::net::SocketAddr::from(([0, 0, 0, 0], 0)));
+
     let accept = headers
         .get("accept")
         .and_then(|v| v.to_str().ok())
@@ -185,6 +199,43 @@ async fn health_handler() -> impl IntoResponse {
     (StatusCode::OK, "ok")
 }
 
+async fn liveness_handler() -> impl IntoResponse {
+    (StatusCode::OK, "ok")
+}
+
+/// Readiness probe — checks MySQL and Redis connectivity.
+///
+/// Returns 200 `{"status":"ready"}` when both are reachable, or
+/// 503 `{"status":"not_ready","mysql":bool,"redis":bool}` otherwise.
+///
+/// Note: Redis pool exhaustion (all connections in use) also returns 503.
+/// This is intentionally conservative — if we can't acquire a connection,
+/// the pod shouldn't receive traffic.
+async fn readiness_handler(State(state): State<Arc<AppState>>) -> impl IntoResponse {
+    use std::time::Duration;
+
+    let check = async {
+        let (mysql_ok, redis_ok) = tokio::join!(state.db.ping(), async {
+            state.redis_pool.get().await.is_ok()
+        },);
+        (mysql_ok, redis_ok)
+    };
+
+    let (mysql_ok, redis_ok) = tokio::time::timeout(Duration::from_secs(2), check)
+        .await
+        .unwrap_or((false, false));
+
+    if mysql_ok && redis_ok {
+        (StatusCode::OK, Json(json!({"status": "ready"}))).into_response()
+    } else {
+        (
+            StatusCode::SERVICE_UNAVAILABLE,
+            Json(json!({"status": "not_ready", "mysql": mysql_ok, "redis": redis_ok})),
+        )
+            .into_response()
+    }
+}
+
 /// Build a CORS layer from the configured origins list.
 ///
 /// If `cors_origins` is empty (dev default), returns a permissive layer.

crates/sprout-relay/src/state.rs

@@ -9,6 +9,7 @@ use tokio::sync::{mpsc, Semaphore};
 use tokio_util::sync::CancellationToken;
 use uuid::Uuid;
 
+use deadpool_redis;
 use sprout_audit::AuditService;
 use sprout_auth::AuthService;
 use sprout_db::Db;
@@ -83,6 +84,8 @@ pub struct AppState {
     pub config: Arc<Config>,
     /// Database connection pool.
     pub db: Db,
+    /// Redis pool for readiness health checks.
+    pub redis_pool: deadpool_redis::Pool,
     /// Audit event service.
     pub audit: Arc<AuditService>,
     /// Pub/sub manager for broadcasting events to subscribers.
@@ -122,6 +125,7 @@ impl AppState {
     pub fn new(
         config: Config,
         db: Db,
+        redis_pool: deadpool_redis::Pool,
         audit: AuditService,
         pubsub: Arc<PubSubManager>,
         auth: AuthService,
@@ -134,6 +138,7 @@ impl AppState {
         Self {
             config: Arc::new(config),
             db,
+            redis_pool,
             audit: Arc::new(audit),
             pubsub,
             auth: Arc::new(auth),