Coordinator: join the cluster when NATS comes up, report the connection

A node that started while NATS was down never got a coordinator. The
connect failed at boot, bootstrap recorded a build error and the node ran
with Coordinator::None until restarted. It had no broadcast subscriber
or publisher, so cross-node push and cache invalidation to it stayed
broken, and its healthcheck said nothing about it. Losing NATS after
startup was silent too.

- The NATS client now connects in the background
  (retry_on_initial_connect): startup never waits on NATS or fails over
  it, the node gets its coordinator, subscriber and publisher at once,
  and the client keeps trying (async-nats's backoff, at most 4 s apart)
  until NATS answers. Subscriptions made meanwhile start delivering when
  it does. A configured maxReconnects still ends the attempts.
- Three new events report the connection: cluster.coordinator-connected
  (info), cluster.coordinator-disconnected (warn: lost, closed, gave up,
  or not connected within the connection timeout at startup) and
  cluster.coordinator-error (warn: a failed attempt, reported once per
  outage rather than every retry, and server errors, slow consumers and
  lame duck mode). They are in the packaged schema, ids 644 to 646.
- GET /healthz/cluster reports the coordinator: 200
  {"coordinator":"connected"}, 503 {"coordinator":"disconnected"}, or
  200 with "none" (no coordinator) or "unknown" (a backend that doesn't
  track its connection). /healthz/live and /healthz/ready are unchanged
  on purpose: a node without its coordinator still serves mail, and
  failing those would have orchestrators restart, or pull out of
  service, every node at once whenever NATS is down.

Only NATS connects lazily; the other coordinator backends still fail at
boot as before.

cluster::coordinator::coordinator_reconnect_tests starts a node against a
NATS port with nothing behind it, checks it boots with a coordinator and
reports it disconnected, subscribes, then starts NATS on that port: the
node connects on its own and the subscription receives a message from a
second client. Stopping and restarting NATS shows disconnected, then
connected, and the same subscription keeps working.

crates/coordinator/Cargo.toml

@@ -8,7 +8,7 @@ store = { path =  "../store" }
 registry = { path =  "../registry" }
 trc = { path = "../trc" }
 futures = { version = "0.3", optional = true }
-tokio = { version = "1.53", features = ["sync", "fs", "io-util"] }
+tokio = { version = "1.53", features = ["sync", "fs", "io-util", "rt", "time"] }
 async-nats = { version = "0.50", default-features = false, features = ["server_2_10", "server_2_11", "aws-lc-rs"], optional = true }
 zenoh = { version = "1.10.0", default-features = false, features = ["auth_pubkey", "transport_multilink", "transport_compression", "transport_quic", "transport_tcp", "transport_tls", "transport_udp"], optional = true }
 rdkafka = { version = "0.39", features = ["cmake-build"], optional = true }

crates/coordinator/src/backend/nats/mod.rs

@@ -2,13 +2,22 @@
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
  *
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
+ *
+ * Modified by Coffey Labs in 2026 for INBUXA.
  */
 
-use std::sync::Arc;
+use std::{
+    sync::{
+        Arc,
+        atomic::{AtomicBool, Ordering},
+    },
+    time::Duration,
+};
 
 use crate::Coordinator;
 use async_nats::Client;
 use registry::schema::structs::NatsCoordinator;
+use trc::ClusterEvent;
 
 pub mod pubsub;
 
@@ -47,9 +56,116 @@ impl NatsPubSub {
             opts = opts.token(credentials);
         }
 
+        // inbuxa: connect in the background and keep trying, so a node that
+        // starts while NATS is down still joins the cluster once NATS is
+        // back, instead of running without a coordinator until restarted;
+        // and report the connection going and coming back
+        let reporter = Arc::new(Reporter::default());
+        opts = opts.retry_on_initial_connect().event_callback({
+            let reporter = reporter.clone();
+            move |event| {
+                let reporter = reporter.clone();
+                async move { reporter.report(event) }
+            }
+        });
+        let connection_timeout = config.timeout_connection.into_inner();
+
         async_nats::connect_with_options(config.addresses.into_inner(), opts)
             .await
-            .map(|client| Coordinator::Nats(Arc::new(NatsPubSub { client })))
+            .map(|client| {
+                reporter.watch_first_connection(client.clone(), connection_timeout);
+                Coordinator::Nats(Arc::new(NatsPubSub { client }))
+            })
             .map_err(|err| format!("Failed to connect to Nats: {}", err))
     }
+
+    /// inbuxa: whether the client is connected to a NATS server right now.
+    pub fn is_connected(&self) -> bool {
+        matches!(
+            self.client.connection_state(),
+            async_nats::connection::State::Connected
+        )
+    }
+}
+
+/// inbuxa: reports the client's connection events as the server's own.
+#[derive(Default)]
+struct Reporter {
+    connected_once: AtomicBool,
+    // A failed attempt raises an error each time the client retries, every
+    // few seconds while NATS is down: report the first after each change
+    error_reported: AtomicBool,
+}
+
+impl Reporter {
+    fn report(&self, event: async_nats::Event) {
+        match event {
+            async_nats::Event::Connected => {
+                self.connected_once.store(true, Ordering::Relaxed);
+                self.error_reported.store(false, Ordering::Relaxed);
+                trc::event!(Cluster(ClusterEvent::CoordinatorConnected), Type = "nats");
+            }
+            async_nats::Event::Disconnected => {
+                self.error_reported.store(false, Ordering::Relaxed);
+                trc::event!(
+                    Cluster(ClusterEvent::CoordinatorDisconnected),
+                    Type = "nats",
+                    Details = "Connection lost; reconnecting in the background",
+                );
+            }
+            async_nats::Event::Closed => {
+                trc::event!(
+                    Cluster(ClusterEvent::CoordinatorDisconnected),
+                    Type = "nats",
+                    Details = "Connection closed; no further attempts will be made",
+                );
+            }
+            async_nats::Event::ClientError(async_nats::ClientError::MaxReconnects) => {
+                trc::event!(
+                    Cluster(ClusterEvent::CoordinatorDisconnected),
+                    Type = "nats",
+                    Details = "Gave up reconnecting (maxReconnects reached)",
+                );
+            }
+            async_nats::Event::ClientError(err) => {
+                if !self.error_reported.swap(true, Ordering::Relaxed) {
+                    trc::event!(
+                        Cluster(ClusterEvent::CoordinatorError),
+                        Type = "nats",
+                        Details = "Connection attempt failed; retrying",
+                        Reason = err.to_string(),
+                    );
+                }
+            }
+            event => {
+                trc::event!(
+                    Cluster(ClusterEvent::CoordinatorError),
+                    Type = "nats",
+                    Details = event.to_string(),
+                );
+            }
+        }
+    }
+
+    /// The first connection is made in the background, so say so when it
+    /// hasn't been made within the connection timeout. The client keeps
+    /// trying, and reports the connection when it comes.
+    fn watch_first_connection(self: &Arc<Self>, client: Client, timeout: Duration) {
+        let reporter = self.clone();
+        tokio::spawn(async move {
+            tokio::time::sleep(timeout).await;
+            if !reporter.connected_once.load(Ordering::Relaxed)
+                && !matches!(
+                    client.connection_state(),
+                    async_nats::connection::State::Connected
+                )
+            {
+                trc::event!(
+                    Cluster(ClusterEvent::CoordinatorDisconnected),
+                    Type = "nats",
+                    Details = "Not connected at startup; retrying in the background",
+                );
+            }
+        });
+    }
 }

crates/coordinator/src/dispatch.rs

@@ -2,6 +2,8 @@
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
  *
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
+ *
+ * Modified by Coffey Labs in 2026 for INBUXA.
  */
 
 use crate::{Coordinator, Msg, PubSubStream};
@@ -43,6 +45,17 @@ impl Coordinator {
     pub fn is_none(&self) -> bool {
         matches!(self, Coordinator::None)
     }
+
+    /// inbuxa: whether the coordinator is connected right now, for the
+    /// backends that track it (NATS); `None` for the others and when no
+    /// coordinator is configured.
+    pub fn is_connected(&self) -> Option<bool> {
+        match self {
+            #[cfg(feature = "nats")]
+            Coordinator::Nats(store) => Some(store.is_connected()),
+            _ => None,
+        }
+    }
 }
 
 impl PubSubStream {

crates/http/src/request.rs

@@ -562,6 +562,27 @@ impl ParseHttp for Server {
                         })
                         .into_http_response());
                     }
+                    // inbuxa: the cluster coordinator's connection, for
+                    // monitoring. It stays out of live and ready on purpose:
+                    // a node without its coordinator still serves mail, and
+                    // failing those would have an orchestrator restart, or
+                    // take out of service, every node at once when the
+                    // coordinator goes down
+                    "cluster" => {
+                        let coordinator = &self.core.storage.coordinator;
+                        let (status, state) = match coordinator.is_connected() {
+                            Some(true) => (StatusCode::OK, "connected"),
+                            Some(false) => (StatusCode::SERVICE_UNAVAILABLE, "disconnected"),
+                            None if coordinator.is_none() => (StatusCode::OK, "none"),
+                            None => (StatusCode::OK, "unknown"),
+                        };
+                        return Ok(http_proto::JsonResponse::with_status(
+                            status,
+                            serde_json::json!({ "coordinator": state }),
+                        )
+                        .no_cache()
+                        .into_http_response());
+                    }
                     _ => (),
                 }
             }

crates/trc/src/event/enums.rs

@@ -10,8 +10,9 @@
 
 // inbuxa: 637 to 641 are the fork's SCIM events (SCIM-54); 642 is
 // auth.legacy-protocol-refused (legacy-protocols LP-6); 643 is
-// security.legacy-protocols-changed (LP-8)
+// security.legacy-protocols-changed (LP-8); 644 to 646 are the cluster
-pub const TOTAL_EVENT_COUNT: usize = 644;
+// coordinator's connection events
+pub const TOTAL_EVENT_COUNT: usize = 647;
 pub const TOTAL_METRIC_COUNT: usize = 369;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -150,6 +151,10 @@ pub enum ClusterEvent {
     MessageSkipped = 47,
     MessageInvalid = 49,
     NodeIdRenewed = 275,
+    // inbuxa: the coordinator's connection
+    CoordinatorConnected = 644,
+    CoordinatorDisconnected = 645,
+    CoordinatorError = 646,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]

crates/trc/src/event/enums_impl.rs

@@ -81,6 +81,10 @@ impl EventType {
             b"cluster.message-skipped" => EventType::Cluster(ClusterEvent::MessageSkipped),
             b"cluster.message-invalid" => EventType::Cluster(ClusterEvent::MessageInvalid),
             b"cluster.node-id-renewed" => EventType::Cluster(ClusterEvent::NodeIdRenewed),
+            // inbuxa: coordinator connection
+            b"cluster.coordinator-connected" => EventType::Cluster(ClusterEvent::CoordinatorConnected),
+            b"cluster.coordinator-disconnected" => EventType::Cluster(ClusterEvent::CoordinatorDisconnected),
+            b"cluster.coordinator-error" => EventType::Cluster(ClusterEvent::CoordinatorError),
             b"dane.authentication-success" => EventType::Dane(DaneEvent::AuthenticationSuccess),
             b"dane.authentication-failure" => EventType::Dane(DaneEvent::AuthenticationFailure),
             b"dane.no-certificates-found" => EventType::Dane(DaneEvent::NoCertificatesFound),
@@ -742,6 +746,14 @@ impl EventType {
             EventType::Cluster(ClusterEvent::MessageSkipped) => "cluster.message-skipped",
             EventType::Cluster(ClusterEvent::MessageInvalid) => "cluster.message-invalid",
             EventType::Cluster(ClusterEvent::NodeIdRenewed) => "cluster.node-id-renewed",
+            // inbuxa: coordinator connection
+            EventType::Cluster(ClusterEvent::CoordinatorConnected) => {
+                "cluster.coordinator-connected"
+            }
+            EventType::Cluster(ClusterEvent::CoordinatorDisconnected) => {
+                "cluster.coordinator-disconnected"
+            }
+            EventType::Cluster(ClusterEvent::CoordinatorError) => "cluster.coordinator-error",
             EventType::Dane(DaneEvent::AuthenticationSuccess) => "dane.authentication-success",
             EventType::Dane(DaneEvent::AuthenticationFailure) => "dane.authentication-failure",
             EventType::Dane(DaneEvent::NoCertificatesFound) => "dane.no-certificates-found",
@@ -1524,6 +1536,10 @@ impl EventType {
             EventType::Cluster(ClusterEvent::MessageSkipped) => 47,
             EventType::Cluster(ClusterEvent::MessageInvalid) => 49,
             EventType::Cluster(ClusterEvent::NodeIdRenewed) => 275,
+            // inbuxa: coordinator connection
+            EventType::Cluster(ClusterEvent::CoordinatorConnected) => 644,
+            EventType::Cluster(ClusterEvent::CoordinatorDisconnected) => 645,
+            EventType::Cluster(ClusterEvent::CoordinatorError) => 646,
             EventType::Dane(DaneEvent::AuthenticationSuccess) => 67,
             EventType::Dane(DaneEvent::AuthenticationFailure) => 66,
             EventType::Dane(DaneEvent::NoCertificatesFound) => 69,
@@ -2176,6 +2192,10 @@ impl EventType {
             47 => Some(EventType::Cluster(ClusterEvent::MessageSkipped)),
             49 => Some(EventType::Cluster(ClusterEvent::MessageInvalid)),
             275 => Some(EventType::Cluster(ClusterEvent::NodeIdRenewed)),
+            // inbuxa: coordinator connection
+            644 => Some(EventType::Cluster(ClusterEvent::CoordinatorConnected)),
+            645 => Some(EventType::Cluster(ClusterEvent::CoordinatorDisconnected)),
+            646 => Some(EventType::Cluster(ClusterEvent::CoordinatorError)),
             67 => Some(EventType::Dane(DaneEvent::AuthenticationSuccess)),
             66 => Some(EventType::Dane(DaneEvent::AuthenticationFailure)),
             69 => Some(EventType::Dane(DaneEvent::NoCertificatesFound)),
@@ -3114,6 +3134,10 @@ impl EventType {
             EventType::Auth(AuthEvent::TooManyAttempts) => Level::Warn,
             EventType::Calendar(CalendarEvent::AlarmFailed) => Level::Warn,
             EventType::Cluster(ClusterEvent::SubscriberDisconnected) => Level::Warn,
+            // inbuxa: coordinator connection
+            EventType::Cluster(ClusterEvent::CoordinatorConnected) => Level::Info,
+            EventType::Cluster(ClusterEvent::CoordinatorDisconnected) => Level::Warn,
+            EventType::Cluster(ClusterEvent::CoordinatorError) => Level::Warn,
             EventType::Delivery(DeliveryEvent::MissingOutboundHostname) => Level::Warn,
             EventType::Delivery(DeliveryEvent::ConcurrencyLimitExceeded) => Level::Warn,
             EventType::Delivery(DeliveryEvent::RateLimitExceeded) => Level::Warn,
@@ -3244,6 +3268,10 @@ impl EventType {
             EventType::Cluster(ClusterEvent::MessageSkipped) => "PubSub message skipped",
             EventType::Cluster(ClusterEvent::MessageInvalid) => "Invalid PubSub message",
             EventType::Cluster(ClusterEvent::NodeIdRenewed) => "Node ID renewed",
+            // inbuxa: coordinator connection
+            EventType::Cluster(ClusterEvent::CoordinatorConnected) => "Coordinator connected",
+            EventType::Cluster(ClusterEvent::CoordinatorDisconnected) => "Coordinator unavailable",
+            EventType::Cluster(ClusterEvent::CoordinatorError) => "Coordinator error",
             EventType::Dane(DaneEvent::AuthenticationSuccess) => "DANE authentication successful",
             EventType::Dane(DaneEvent::AuthenticationFailure) => "DANE authentication failed",
             EventType::Dane(DaneEvent::NoCertificatesFound) => "No certificates found for DANE",
@@ -4322,6 +4350,10 @@ impl EventType {
             EventType::Cluster(ClusterEvent::MessageSkipped),
             EventType::Cluster(ClusterEvent::MessageInvalid),
             EventType::Cluster(ClusterEvent::NodeIdRenewed),
+            // inbuxa: coordinator connection
+            EventType::Cluster(ClusterEvent::CoordinatorConnected),
+            EventType::Cluster(ClusterEvent::CoordinatorDisconnected),
+            EventType::Cluster(ClusterEvent::CoordinatorError),
             EventType::Dane(DaneEvent::AuthenticationSuccess),
             EventType::Dane(DaneEvent::AuthenticationFailure),
             EventType::Dane(DaneEvent::NoCertificatesFound),

resources/schema/schema.json.sha256

@@ -1 +1 @@
-VbnFuwCOTBh0s2T-NuRhb2JaJr8Jl5s3LgXv4Pv2sTg
+XFI3xuKC_rH1KZyaVBF0uTIiRDXRqyYboijquiGz2eg

tests/src/cluster/coordinator.rs

@@ -0,0 +1,145 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+//! A node that starts while its NATS coordinator is down joins the cluster
+//! once NATS comes up, without a restart, and reports the coordinator's
+//! connection on `/healthz/cluster` as it goes and comes back.
+
+use crate::utils::server::TestServerBuilder;
+use coordinator::Coordinator;
+use registry::{
+    schema::{
+        enums::NetworkListenerProtocol,
+        structs::{Coordinator as CoordinatorSetting, NatsCoordinator},
+    },
+    types::map::Map,
+};
+use serde_json::{Value, json};
+use std::time::{Duration, Instant};
+use testcontainers::{
+    GenericImage, ImageExt, core::IntoContainerPort, core::WaitFor, runners::AsyncRunner,
+};
+
+const HTTP_PORT: u16 = 11_310;
+const TOPIC: &str = "inbuxa-coordinator-test";
+
+#[tokio::test(flavor = "multi_thread")]
+pub async fn coordinator_reconnect_tests() {
+    println!("Running coordinator reconnect tests...");
+
+    // A port with no NATS server behind it, yet
+    let nats_port = std::net::TcpListener::bind("127.0.0.1:0")
+        .unwrap()
+        .local_addr()
+        .unwrap()
+        .port();
+    let config = NatsCoordinator {
+        addresses: Map::new(vec![format!("127.0.0.1:{nats_port}")]),
+        use_tls: false,
+        timeout_connection: 1_000u64.into(),
+        ..Default::default()
+    };
+
+    // 1. The node starts, without a build error, while NATS is down, and
+    // says so
+    let test = TestServerBuilder::new("coordinator_reconnect_tests")
+        .await
+        .with_object(CoordinatorSetting::Nats(config.clone()))
+        .await
+        .with_listener(NetworkListenerProtocol::Http, "http", HTTP_PORT, true)
+        .await
+        .build()
+        .await;
+    let coordinator = test.server.core.storage.coordinator.clone();
+    assert!(
+        coordinator.is_enabled(),
+        "a coordinator, though not connected"
+    );
+    assert_eq!(coordinator.is_connected(), Some(false));
+    assert_eq!(
+        cluster_health().await,
+        (503, json!({"coordinator": "disconnected"}))
+    );
+
+    // A subscription made now, as the broadcast subscriber makes it at
+    // startup, has to work once NATS is up
+    let mut stream = coordinator.subscribe(TOPIC).await.unwrap();
+
+    // 2. NATS comes up: the node connects on its own
+    let nats = GenericImage::new("nats", "latest")
+        .with_wait_for(WaitFor::message_on_stderr("Server is ready"))
+        .with_mapped_port(nats_port, 4222.tcp())
+        .start()
+        .await
+        .expect("Failed to start NATS container");
+    wait_for_health(200, "connected").await;
+    let other_node = coordinator::backend::nats::NatsPubSub::open(config.clone())
+        .await
+        .unwrap();
+    wait_until_connected(&other_node).await;
+    round_trip(&other_node, &mut stream, b"after startup").await;
+
+    // 3. NATS goes away: the node reports it; and it comes back: the node
+    // reconnects and the same subscription carries on
+    nats.stop().await.unwrap();
+    wait_for_health(503, "disconnected").await;
+    nats.start().await.unwrap();
+    wait_for_health(200, "connected").await;
+    wait_until_connected(&other_node).await;
+    round_trip(&other_node, &mut stream, b"after reconnect").await;
+
+    drop(nats);
+    if test.is_reset() {
+        test.temp_dir.delete();
+    }
+}
+
+async fn cluster_health() -> (u16, Value) {
+    let response = reqwest::Client::builder()
+        .danger_accept_invalid_certs(true)
+        .timeout(Duration::from_secs(5))
+        .build()
+        .unwrap()
+        .get(format!("https://127.0.0.1:{HTTP_PORT}/healthz/cluster"))
+        .send()
+        .await
+        .unwrap();
+    let status = response.status().as_u16();
+    (status, response.json().await.unwrap())
+}
+
+async fn wait_for_health(status: u16, state: &str) {
+    let started = Instant::now();
+    loop {
+        let health = cluster_health().await;
+        if health == (status, json!({"coordinator": state})) {
+            return;
+        }
+        assert!(
+            started.elapsed() < Duration::from_secs(30),
+            "expected {status} {state}, still {health:?}"
+        );
+        tokio::time::sleep(Duration::from_millis(250)).await;
+    }
+}
+
+async fn wait_until_connected(coordinator: &Coordinator) {
+    let started = Instant::now();
+    while coordinator.is_connected() != Some(true) {
+        assert!(started.elapsed() < Duration::from_secs(30), "not connected");
+        tokio::time::sleep(Duration::from_millis(100)).await;
+    }
+}
+
+/// Another node publishes; this one's subscription receives it.
+async fn round_trip(from: &Coordinator, stream: &mut coordinator::PubSubStream, payload: &[u8]) {
+    from.publish(TOPIC, payload.to_vec()).await.unwrap();
+    let message = tokio::time::timeout(Duration::from_secs(10), stream.next())
+        .await
+        .expect("no message within 10 seconds")
+        .expect("subscription ended");
+    assert_eq!(message.payload(), payload);
+}

tests/src/cluster/mod.rs

@@ -2,7 +2,11 @@
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
  *
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
+ *
+ * Modified by Coffey Labs in 2026 for INBUXA.
  */
 
 pub mod broadcast;
+#[cfg(feature = "nats")]
+pub mod coordinator; // inbuxa: coordinator reconnects
 pub mod stress;