What causes "Connect/auth failed for {}" in apache/seatunnel?

Verify the endpoint host:port is correct and the receiver is listening (`nc -vz host port`).

Connect/auth failed for

Error message

Connect/auth failed for {}

What it means

EdgeTransportClient.ensureAuthenticatedSession tries to establish and authenticate a socket to the configured endpoint. On connect or auth failure it closes the socket, logs 'Connect/auth failed for {endpoint}' with the exception, doubles the backoff up to maxBackoffMs, sleeps, and retries. The client eventually succeeds or the caller's timeout/interrupt surfaces the underlying error.

Solutions

Verify the endpoint host:port is correct and the receiver is listening (`nc -vz host port`).
Check agent credentials/token against the receiver's current auth config (rotation is the usual culprit).
Open firewall/security-group rules for the transport port.
Review backoff logs: repeated failures with growing backoff indicate a persistent config/network problem, not a transient one.

Example fix

// before: wrong port after receiver reconfiguration
transport {
  endpoint = "10.0.0.5:5801"
}
// after
transport {
  endpoint = "10.0.0.5:5802"
}

Defensive patterns

Strategy: retry

Validate before calling

# Validate endpoint and auth before starting the agent
nc -zv "$HOST" "$PORT" || echo 'endpoint unreachable'
# verify credential freshness
./agent auth verify --endpoint "$ENDPOINT"

Try / catch

try {
    client.open();
} catch (IOException e) {
    // after repeated 'Connect/auth failed' warnings with max backoff,
    // escalate: check endpoint reachability and rotate credentials
    alert("transport cannot connect to " + endpoint + ": " + e.getMessage());
}

Prevention

Validate endpoint host:port in agent config at startup.
Automate credential/token rotation and verify before expiry.
Open firewall rules for the transport port in every environment.
Watch backoff patterns: capped max-backoff retries signal persistent config problems.

When it happens

Trigger: open() or sendUntilReceived() -> session establishment fails: TCP connect refused/timed out, or authentication handshake rejected (bad credentials/token, protocol mismatch).

Common situations: Receiver not started or listening on a different port, firewall blocking the port, expired/rotated auth credentials on the agent, or hostname misconfiguration in the endpoint.

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 apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/5f4208cd8cee85d3. Report an issue: GitHub.

Appendix: source

Thrown at seatunnel-edge-agent/seatunnel-edge-agent-transport/src/main/java/org/apache/seatunnel/edge/agent/transport/socket/EdgeTransportClient.java:186

                return;
            } catch (EdgeSocketCollectorRejectedException ex) {
                if (socket != null) {
                    try {
                        socket.close();
                    } catch (IOException closeEx) {
                        LOG.debug("Error closing socket after REJECTED", closeEx);
                    }
                }
                throw ex;
            } catch (IOException connectOrAuthEx) {
                if (socket != null) {
                    try {
                        socket.close();
                    } catch (IOException closeEx) {
                        LOG.debug("Error closing socket after connect/auth failure", closeEx);
                    }
                }
                LOG.warn("Connect/auth failed for {}", endpoint, connectOrAuthEx);
                backoff =
                        Math.min(
                                config.getMaxBackoffMs(),
                                Math.max(backoff, config.getInitialBackoffMs()) * 2);
                EdgeTransportConfig.sleepQuiet(backoff);
            }
        }
        throw new IOException(
                "Cannot connect to edge ingress "
                        + endpoint
                        + " after "
                        + config.getMaxReconnectCycles()
                        + " cycles");
    }

    private static final class SocketHolder implements AutoCloseable {
        private final Socket socket;
        private final BufferedReader reader;

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