nautechsystems/nautilus_trader · error · anyhow::Error

Failed to connect to {} after {} attempts: {}. If this is a

Error message

Failed to connect to {} after {} attempts: {}. If this is a DNS error, check your network configuration and DNS settings.

What it means

SocketClient.connect_url retries the connection up to max_retries times; if every attempt fails, it bails with this aggregated error containing the URL, attempt count, and the last underlying error, plus a DNS-specific hint. It is the terminal failure of the connect loop, not a per-attempt error.

Source

Thrown at crates/network/src/socket/client.rs:195

                        config.url,
                    );
                    error
                }
                Err(_) => {
                    let error = format!(
                        "Connection timeout after {:.1}s (possible DNS resolution failure)",
                        connect_timeout.as_secs_f64()
                    );
                    log::warn!(
                        "Socket connection attempt {attempt}/{max_retries} to {} timed out",
                        config.url,
                    );
                    error
                }
            };

            if attempt >= max_retries {
                anyhow::bail!(
                    "Failed to connect to {} after {} attempts: {}. \
                    If this is a DNS error, check your network configuration and DNS settings.",
                    config.url,
                    max_retries,
                    last_error,
                );
            }

            let delay = backoff.next_duration();
            log::debug!(
                "Retrying in {delay:?} (attempt {}/{})",
                attempt + 1,
                max_retries
            );
            dst::time::sleep(delay).await;
        };

        log::debug!("Connected");

View on GitHub (pinned to 18893faf8b)

Solutions

Read the embedded last_error to distinguish DNS failure vs connection refused vs TLS failure.
Verify the URL hostname/port and that the endpoint is reachable (ping/curl from the same host).
Check DNS configuration (resolv.conf, corporate resolver, container network).
Increase max_retries or add backoff if the endpoint is slow to come up; ensure the server is running before connecting.

Example fix

// before
let client = SocketClient::connect(config, None).await?; // fails when server is down
// after
ensure_server_up("wss://stream.example.com/ws");
let client = match SocketClient::connect(config, None).await {
    Ok(c) => c,
    Err(e) => { log::error!("connect failed: {e}"); return Err(e); }
};

Defensive patterns

Strategy: retry

Validate before calling

// Rust: pre-check DNS resolution before connecting
let host = url.host_str().ok_or_else(|| anyhow::anyhow!("no host in {url}"))?;
tokio::net::lookup_host((host, 443)).await.map_err(|e| anyhow::anyhow!("DNS failed for {host}: {e}"))?;

Try / catch

match SocketClient::connect(config, None).await {
    Ok(c) => c,
    Err(e) if e.to_string().contains("DNS") => {
        tokio::time::sleep(Duration::from_secs(5)).await;
        SocketClient::connect(config, None).await
    }
    Err(e) => Err(e),
}

Prevention

Verify endpoint URLs against provider docs.
Ensure the server is up before clients connect.
Check container/corporate DNS settings.
Use health checks + bounded retries with backoff.

When it happens

Trigger: Connecting to an unreachable/unresolvable socket URL so all retry attempts fail: wrong host/port, server down, firewall block, or DNS resolution failure — then attempt >= max_retries is reached.

Common situations: Typo in websocket endpoint hostname; exchange endpoint blocked by network policy/region; Docker/K8s DNS misconfiguration; server not started before client connects; stale endpoint after provider API version change.

Understand the failure class

Background: ECONNREFUSED and "connection refused" / "could not connect to server" errors: what they mean and how to fix them — this error's family across 44 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/bdeb415545730869. Report an issue: GitHub.