Don't error if local listen port is already in use

binaries/daemon/src/local_listener.rs

@@ -19,9 +19,15 @@ pub struct DynamicNodeEventWrapper {
 pub async fn spawn_listener_loop(
     bind: SocketAddr,
     events_tx: flume::Sender<Timestamped<DynamicNodeEventWrapper>>,
-) -> eyre::Result<u16> {
+) -> eyre::Result<Option<u16>> {
     let socket = match TcpListener::bind(bind).await {
         Ok(socket) => socket,
+        Err(err) if err.kind() == ErrorKind::AddrInUse => {
+            tracing::warn!(
+                "Daemon listen port already in use. There might be another daemon running already."
+            );
+            return Ok(None);
+        }
         Err(err) => {
             return Err(eyre::Report::new(err).wrap_err("failed to create local TCP listener"))
         }
@@ -35,7 +41,7 @@ pub async fn spawn_listener_loop(
         listener_loop(socket, events_tx).await;
     });
 
-    Ok(listen_port)
+    Ok(Some(listen_port))
 }
 
 async fn listener_loop(

examples/multiple-daemons/run.rs

@@ -54,8 +54,8 @@ async fn main() -> eyre::Result<()> {
     )
     .await?;
     let coordinator_addr = Ipv4Addr::LOCALHOST;
-    let daemon_a = run_daemon(coordinator_addr.to_string(), "A", 9843); // Random port
-    let daemon_b = run_daemon(coordinator_addr.to_string(), "B", 9842);
+    let daemon_a = run_daemon(coordinator_addr.to_string(), "A");
+    let daemon_b = run_daemon(coordinator_addr.to_string(), "B");
 
     tracing::info!("Spawning coordinator and daemons");
     let mut tasks = JoinSet::new();
@@ -221,11 +221,7 @@ async fn build_dataflow(dataflow: &Path) -> eyre::Result<()> {
     Ok(())
 }
 
-async fn run_daemon(
-    coordinator: String,
-    machine_id: &str,
-    local_listen_port: u16,
-) -> eyre::Result<()> {
+async fn run_daemon(coordinator: String, machine_id: &str) -> eyre::Result<()> {
     let cargo = std::env::var("CARGO").unwrap();
     let mut cmd = tokio::process::Command::new(&cargo);
     cmd.arg("run");
@@ -237,7 +233,7 @@ async fn run_daemon(
         .arg("--coordinator-addr")
         .arg(coordinator)
         .arg("--local-listen-port")
-        .arg(local_listen_port.to_string());
+        .arg("9843"); // random port
     if !cmd.status().await?.success() {
         bail!("failed to run dataflow");
     };