feat(maker): Monitor and expose status of services connected

Monitor the following services:
    - coordinator
    - orderbook (we don't subscribe to orderbook feed yet)

in order to derive health status of the maker.

Health status is exposed via the HTTP API as well as reported as
dedicated prometheus metrics.

TODO: Subscribe to orderbook websocket stream to be able to detect if it is down
TODO: Subcribe to bitmex client stream to be able to spot outdated information

almost there, just exposing HTTP API

I still need to show quickly how to return different HTTP errors based on health status

maker/src/bin/maker.rs

@@ -7,6 +7,7 @@ use ln_dlc_node::node::InMemoryStore;
 use ln_dlc_node::node::LnDlcNodeSettings;
 use ln_dlc_node::seed::Bip39Seed;
 use maker::cli::Opts;
+use maker::health;
 use maker::ln::ldk_config;
 use maker::ln::EventHandler;
 use maker::logger;
@@ -88,31 +89,49 @@ async fn main() -> Result<()> {
     let _running_node = node.start(event_handler)?;
 
     let node_pubkey = node.info.pubkey;
-    tokio::spawn(async move {
-        match trading::run(
-            &opts.orderbook,
-            node_pubkey,
-            network,
-            opts.concurrent_orders,
-            time::Duration::seconds(opts.order_expiry_after_seconds as i64),
-        )
-        .await
-        {
-            Ok(()) => {
-                tracing::error!("Maker stopped trading");
-            }
-            Err(error) => {
-                tracing::error!("Maker stopped trading: {error:#}");
+    tokio::spawn({
+        let orderbook = opts.orderbook.clone();
+        async move {
+            match trading::run(
+                &orderbook,
+                node_pubkey,
+                network,
+                opts.concurrent_orders,
+                time::Duration::seconds(opts.order_expiry_after_seconds as i64),
+            )
+            .await
+            {
+                Ok(()) => {
+                    tracing::error!("Maker stopped trading");
+                }
+                Err(error) => {
+                    tracing::error!("Maker stopped trading: {error:#}");
+                }
             }
         }
     });
 
-    tokio::spawn({
+    let (health, health_tx) = health::Health::new();
+
+    let _monitor_coordinator_status = tokio::spawn({
+        let endpoint = opts.orderbook.clone();
+        let client = reqwest_client();
+        let interval = Duration::from_secs(10);
+        async move {
+            health::check_health_endpoint(&client, endpoint, health_tx.coordinator, interval).await;
+        }
+    });
+
+    // TODO: Monitor orderbook websocket stream with `health_tx.orderbook` when we subscribe to it
+
+    let _collect_prometheus_metrics = tokio::spawn({
         let node = node.clone();
+        let health = health.clone();
         async move {
             loop {
                 let node = node.clone();
-                spawn_blocking(move || metrics::collect(node))
+                let health = health.clone();
+                spawn_blocking(move || metrics::collect(node, health))
                     .await
                     .expect("To spawn blocking thread");
                 tokio::time::sleep(PROCESS_PROMETHEUS_METRICS).await;
@@ -128,7 +147,7 @@ async fn main() -> Result<()> {
     let mut conn = pool.get().expect("to get connection from pool");
     run_migration(&mut conn);
 
-    let app = router(node, exporter, pool);
+    let app = router(node, exporter, pool, health);
 
     // Start the metrics exporter
     autometrics::prometheus_exporter::init();
@@ -150,3 +169,9 @@ async fn main() -> Result<()> {
 
     Ok(())
 }
+fn reqwest_client() -> reqwest::Client {
+    reqwest::Client::builder()
+        .timeout(std::time::Duration::from_secs(30))
+        .build()
+        .expect("Failed to build reqwest client")
+}

maker/src/health.rs

@@ -0,0 +1,120 @@
+// TODO: Add health collection metrics
+// This can be later used to add health metrics to the health endpoint
+
+use anyhow::bail;
+use anyhow::Context;
+use anyhow::Result;
+use reqwest::Client;
+use reqwest::StatusCode;
+use reqwest::Url;
+use std::time::Duration;
+use tokio::sync::watch;
+
+/// Health status of a service
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
+pub enum ServiceStatus {
+    #[default]
+    Unknown,
+    Online,
+    Offline,
+}
+
+/// Health monitoring for the node
+///
+/// Simple endpoint querying is handled by provided configuration, for more complex health checks
+/// the transmitters are exposed to be plugged in the services that need to publish their health
+/// status.
+
+#[derive(Clone)]
+pub struct Health {
+    /// Coordinator HTTP API status
+    coordinator_rx: watch::Receiver<ServiceStatus>,
+    /// Orderbook websocket stream status
+    orderbook_rx: watch::Receiver<ServiceStatus>,
+}
+
+/// Transmitters that need to be plugged in the services that need to publish their health status.
+pub struct Tx {
+    pub orderbook: watch::Sender<ServiceStatus>,
+    pub coordinator: watch::Sender<ServiceStatus>,
+}
+
+impl Health {
+    pub fn new() -> (Self, Tx) {
+        let (orderbook_tx, orderbook_rx) = watch::channel(ServiceStatus::Unknown);
+        let (coordinator_tx, coordinator_rx) = watch::channel(ServiceStatus::Unknown);
+
+        (
+            Self {
+                coordinator_rx,
+                orderbook_rx,
+            },
+            Tx {
+                orderbook: orderbook_tx,
+                coordinator: coordinator_tx,
+            },
+        )
+    }
+
+    // TODO: Any ideas of the most useful way of sending this information?
+    // - perhaps a serialized struct (json) with the status of each service?
+    pub fn get_health(&self) -> Result<String> {
+        let mut health_info = String::new();
+        health_info.push_str(&format!(
+            "Coordinator: {:?}\n",
+            self.get_coordinator_status()
+        ));
+        health_info.push_str(&format!("Orderbook: {:?}\n", self.get_orderbook_status()));
+
+        if self.get_coordinator_status() == ServiceStatus::Online
+        // TODO: Uncomment this line when we retrieve the orderbook status
+        // && (self.get_orderbook_status() == ServiceStatus::Online)
+        {
+            Ok(health_info)
+        } else {
+            bail!("Status: ERROR\n + {health_info}");
+        }
+    }
+
+    pub fn get_coordinator_status(&self) -> ServiceStatus {
+        *self.coordinator_rx.borrow()
+    }
+
+    pub fn get_orderbook_status(&self) -> ServiceStatus {
+        *self.orderbook_rx.borrow()
+    }
+    // TODO: Add bitmex status? would anything else be useful here?
+}
+
+/// Simple way of checking if a service is online or offline
+pub async fn check_health_endpoint(
+    client: &Client,
+    endpoint: Url,
+    tx: watch::Sender<ServiceStatus>,
+    interval: Duration,
+) {
+    loop {
+        let status = if check_endpoint_availability(client, endpoint.clone())
+            .await
+            .is_ok()
+        {
+            ServiceStatus::Online
+        } else {
+            ServiceStatus::Offline
+        };
+
+        tx.send(status).expect("Receiver not to be dropped");
+        tokio::time::sleep(interval).await;
+    }
+}
+
+async fn check_endpoint_availability(client: &Client, endpoint: Url) -> Result<StatusCode> {
+    tracing::trace!(%endpoint, "Sending request to check health");
+    let response = client
+        .get(endpoint)
+        .send()
+        .await
+        .context("could not send request")?
+        .error_for_status()?;
+    Ok(response.status())
+}

maker/src/lib.rs

@@ -7,6 +7,7 @@ use diesel_migrations::MigrationHarness;
 mod tests;
 
 pub mod cli;
+pub mod health;
 pub mod ln;
 pub mod logger;
 pub mod metrics;

maker/src/metrics.rs

@@ -1,3 +1,5 @@
+use crate::health::Health;
+use crate::health::ServiceStatus;
 use lazy_static::lazy_static;
 use lightning::ln::channelmanager::ChannelDetails;
 use ln_dlc_node::node::InMemoryStore;
@@ -16,7 +18,16 @@ use std::sync::Arc;
 use std::time::Duration;
 
 lazy_static! {
-    pub static ref METER: Meter = global::meter("coordinator");
+    pub static ref METER: Meter = global::meter("maker");
+
+    // health metrics
+    pub static ref COORDINATOR_STATUS: ObservableGauge<u64> = METER.u64_observable_gauge("coordinator_status")
+        .with_description("Coordinator status")
+        .init();
+
+    pub static ref ORDERBOOK_STATUS: ObservableGauge<u64> = METER.u64_observable_gauge("orderbook_status")
+        .with_description("Orderbook status")
+        .init();
 
     // channel details metrics
     pub static ref CHANNEL_BALANCE_SATOSHI: ObservableGauge<u64> = METER
@@ -58,12 +69,42 @@ pub fn init_meter() -> PrometheusExporter {
     opentelemetry_prometheus::exporter(controller).init()
 }
 
-pub fn collect(node: Arc<Node<InMemoryStore>>) {
+pub fn collect(node: Arc<Node<InMemoryStore>>, health: Health) {
     let cx = opentelemetry::Context::current();
 
     let channels = node.channel_manager.list_channels();
     channel_metrics(&cx, channels);
     node_metrics(&cx, node);
+    health_metrics(&cx, &health);
+}
+
+fn health_metrics(cx: &Context, health: &Health) {
+    update_health_metric(cx, health.get_coordinator_status(), &COORDINATOR_STATUS);
+    update_health_metric(cx, health.get_orderbook_status(), &ORDERBOOK_STATUS);
+}
+
+/// Updates the health metric given a service status
+fn update_health_metric(cx: &Context, service_status: ServiceStatus, gauge: &ObservableGauge<u64>) {
+    match service_status {
+        ServiceStatus::Unknown => {
+            gauge.observe(cx, 0, &[KeyValue::new("status", "unknown")]);
+        }
+        ServiceStatus::Online => {
+            gauge.observe(cx, 1, &[KeyValue::new("status", "online")]);
+        }
+        ServiceStatus::Offline => {
+            gauge.observe(cx, 0, &[KeyValue::new("status", "offline")]);
+        }
+    }
+
+    // let _ = check_endpoint_availability(client, "http://localhost:8080/health").await.map(|status| match status {
+    //     StatusCode::OK => {
+    //         COORDINATOR_STATUS.observe(cx, 1, &[KeyValue::new("status", "ok")]);
+    //     }
+    //     _ => {
+    //         COORDINATOR_STATUS.observe(cx, 0, &[KeyValue::new("status", "error")]);
+    //     }
+    // });
 }
 
 fn channel_metrics(cx: &Context, channels: Vec<ChannelDetails>) {

maker/src/routes.rs

@@ -1,3 +1,4 @@
+use crate::health::Health;
 use axum::extract::Path;
 use axum::extract::State;
 use axum::http::StatusCode;
@@ -29,17 +30,20 @@ pub struct AppState {
     pub node: Arc<Node<InMemoryStore>>,
     pub exporter: PrometheusExporter,
     pub pool: Pool<ConnectionManager<PgConnection>>,
+    pub health: Health,
 }
 
 pub fn router(
     node: Arc<Node<InMemoryStore>>,
     exporter: PrometheusExporter,
     pool: Pool<ConnectionManager<PgConnection>>,
+    health: Health,
 ) -> Router {
     let app_state = Arc::new(AppState {
         node,
         exporter,
         pool,
+        health,
     });
 
     Router::new()
@@ -52,6 +56,7 @@ pub fn router(
         .route("/api/pay-invoice/:invoice", post(pay_invoice))
         .route("/api/sync-on-chain", post(sync_on_chain))
         .route("/metrics", get(get_metrics))
+        .route("/health", get(get_health))
         .with_state(app_state)
 }
 
@@ -267,3 +272,12 @@ pub async fn get_metrics(State(state): State<Arc<AppState>>) -> impl IntoRespons
 
     (StatusCode::OK, open_telemetry_metrics + &autometrics)
 }
+
+/// Returns 500 if any of the vital services are offline
+pub async fn get_health(State(state): State<Arc<AppState>>) -> Result<Json<String>, AppError> {
+    let resp = state
+        .health
+        .get_health()
+        .map_err(|e| AppError::InternalServerError(format!("Error: {e:#}")))?;
+    Ok(Json(resp))
+}