apache/seatunnel · critical · ClickhouseConnectorException

Failed to connect to host: " + host + " by user: " + user +

Error message

Failed to connect to host: " + host + " by user: " + user + " on port 22

What it means

ScpFileTransfer.init() catches IOException or GeneralSecurityException during connection/auth setup and rethrows it as SSH_OPERATION_FAILED with a 'Failed to connect to host ... on port 22' message. This is the generic SSH connect failure — the TCP/SSH handshake or crypto setup failed before authentication could be evaluated.

Source

Thrown at seatunnel-connectors-v2/connector-clickhouse/src/main/java/org/apache/seatunnel/connectors/seatunnel/clickhouse/sink/file/ScpFileTransfer.java:87

            clientSession = sshClient.connect(user, host, SCP_PORT).verify().getSession();
            if (password != null) {
                clientSession.addPasswordIdentity(password);
            }
            if (keyPath != null) {
                FileKeyPairProvider fileKeyPairProvider =
                        new FileKeyPairProvider(Paths.get(keyPath));
                KeyPair fileKeyPair =
                        fileKeyPairProvider.loadKey(clientSession, KeyPairProvider.SSH_RSA);
                clientSession.addPublicKeyIdentity(fileKeyPair);
            }
            if (!clientSession.auth().verify().isSuccess()) {
                throw new ClickhouseConnectorException(
                        ClickhouseConnectorErrorCode.SSH_OPERATION_FAILED,
                        "ssh host " + host + "authentication failed");
            }
            scpClient = ScpClientCreator.instance().createScpClient(clientSession);
        } catch (IOException | GeneralSecurityException e) {
            throw new ClickhouseConnectorException(
                    ClickhouseConnectorErrorCode.SSH_OPERATION_FAILED,
                    "Failed to connect to host: " + host + " by user: " + user + " on port 22",
                    e);
        }
    }

    @Override
    public void transferAndChown(String sourcePath, String targetPath) {
        try {
            scpClient.upload(
                    sourcePath,
                    targetPath,
                    ScpClient.Option.Recursive,
                    ScpClient.Option.TargetIsDirectory,
                    ScpClient.Option.PreserveAttributes);
        } catch (IOException e) {
            throw CommonError.fileOperationFailed(
                    "ClickhouseFile", "transfer", sourcePath + " -> " + targetPath, e);

View on GitHub (pinned to cf67b549a7)

Solutions

1. Test connectivity from the SeaTunnel worker: nc -vz <host> 22 or ssh user@host
2. Verify the host address and that sshd is running on the remote machine
3. Open port 22 in firewalls/security groups between worker and host
4. Confirm the key file at keyPath exists and is readable by the process user (check permissions and path)
5. Note the message hardcodes 'port 22'; if a custom port is used in config, ignore that part and check the actual configured port

Example fix

// before: unreachable host
host = "10.0.0.99"
// after: correct, reachable host (and open port 22)
host = "10.0.0.10"

# pre-flight connectivity check from the SeaTunnel worker host
nc -vz -w 5 "$HOST" 22 && echo ssh-port-open
[ -r "$KEY_PATH" ] && echo key-readable

try {
    transfer.init();
} catch (ClickhouseConnectorException e) {
    if (String.valueOf(e.getMessage()).startsWith("Failed to connect to host")) {
        // inspect e.getCause(): UnknownHost vs ConnectException vs timeout vs security
        log.error("SSH connect failed to {} : {}", host, e.getCause());
    }
    throw e;
}

When it happens

Trigger: new connect to host:22 throws (connection refused/timeout/unreachable/DNS failure) or key loading throws GeneralSecurityException (unreadable/corrupt key file at keyPath).

Common situations: Firewall or security group blocking port 22, wrong host/port in config, remote sshd not running, DNS misresolution, or the SSH key file missing/unreadable by the SeaTunnel worker process.

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

• Failed to close ssh session
• Failed to close ssh client
• Failed to connect to host: " + host + " by user: " + user +
• Failed to close ssh session
• Failed to close ssh client

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/9d5042d27638c265. Report an issue: GitHub.