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我在尝试多次访问 ftp 时遇到了一些问题。例如，我们在 ftp 中有数百个文件，我尝试在每个请求/端点命中时下载一个。在随机连接数之后，日志显示有一段时间我们不再可以登录到 ftp，但在进一步的过程中它会自行纠正。这可能是由于短时间内请求过多造成的吗？非常感谢提高连接可靠性的任何想法？

2021-02-24 14:56:02.601 +00:00 [Information] Status:   Connecting to xx.xx.xx.xx:21
2021-02-24 14:56:02.613 +00:00 [Information] Response: 220 Microsoft FTP Service
2021-02-24 14:56:02.614 +00:00 [Information] Status:   Detected FTP server: WindowsServerIIS
2021-02-24 14:56:02.617 +00:00 [Information] Command:  AUTH TLS
2021-02-24 14:56:02.624 +00:00 [Information] Response: 234 AUTH command ok. Expecting TLS Negotiation.
2021-02-24 14:56:02.629 +00:00 [Information] Status:   FTPS Authentication Successful
2021-02-24 14:56:02.630 +00:00 [Information] Command:  USER xxx\$xxxftp
2021-02-24 14:56:02.634 +00:00 [Information] Response: 331 Password required
2021-02-24 14:56:02.635 +00:00 [Information] Command:  PASS ***
2021-02-24 14:56:02.696 +00:00 [Information] Response: 230 User logged in.
2021-02-24 14:56:02.697 +00:00 [Information] Command:  PBSZ 0
2021-02-24 14:56:02.702 +00:00 [Information] Response: 200 PBSZ command successful.
2021-02-24 14:56:02.703 +00:00 [Information] Command:  PROT P
2021-02-24 14:56:02.707 +00:00 [Information] Response: 200 PROT command successful.
2021-02-24 14:56:02.708 +00:00 [Information] Command:  FEAT
2021-02-24 14:56:02.711 +00:00 [Information] Response: 211 END
2021-02-24 14:56:02.712 +00:00 [Information] Status:   Text encoding: System.Text.UTF8Encoding+UTF8EncodingSealed
2021-02-24 14:56:02.713 +00:00 [Information] Command:  OPTS UTF8 ON
2021-02-24 14:56:02.716 +00:00 [Information] Response: 200 OPTS UTF8 command successful - UTF8 encoding now ON.
2021-02-24 14:56:02.716 +00:00 [Information] Command:  SYST
2021-02-24 14:56:02.719 +00:00 [Information] Response: 215 Windows_NT
2021-02-24 14:56:02.720 +00:00 [Information] Command:  TYPE I
2021-02-24 14:56:02.723 +00:00 [Information] Response: 200 Type set to I.
2021-02-24 14:56:02.724 +00:00 [Information] Command:  PASV
2021-02-24 14:56:02.727 +00:00 [Information] Response: 227 Entering Passive Mode (52,166,149,149,40,6).
2021-02-24 14:56:02.728 +00:00 [Information] Status:   Connecting to xx.xx.xx.xx:10246
2021-02-24 14:56:02.731 +00:00 [Information] Command:  RETR /site/ftp/xxx.pdf
2021-02-24 14:56:02.736 +00:00 [Information] Response: 125 Data connection already open; Transfer starting.
2021-02-24 14:56:02.741 +00:00 [Information] Status:   FTPS Authentication Successful
2021-02-24 14:56:02.835 +00:00 [Information] Response: 226 Transfer complete.
2021-02-24 14:56:02.836 +00:00 [Information] Command:  QUIT
2021-02-24 14:56:02.842 +00:00 [Information] Response: 221 Goodbye.
2021-02-24 14:56:02.854 +00:00 [Information] Status:   Connecting to 52.166.149.149:21
2021-02-24 14:56:02.861 +00:00 [Information] Response: 220 Microsoft FTP Service
2021-02-24 14:56:02.861 +00:00 [Information] Status:   Detected FTP server: WindowsServerIIS
2021-02-24 14:56:02.862 +00:00 [Information] Command:  AUTH TLS
2021-02-24 14:56:02.865 +00:00 [Information] Response: 234 AUTH command ok. Expecting TLS Negotiation.
2021-02-24 14:56:02.870 +00:00 [Information] Status:   FTPS Authentication Successful
2021-02-24 14:56:02.872 +00:00 [Information] Command:  USER xxxftp\$xxxftp
2021-02-24 14:56:02.874 +00:00 [Information] Response: 331 Password required
2021-02-24 14:56:02.875 +00:00 [Information] Command:  PASS ***
2021-02-24 14:56:02.884 +00:00 [Information] Response: 530 User cannot log in.
2021-02-24 14:56:02.884 +00:00 [Information] Command:  QUIT
2021-02-24 14:56:02.887 +00:00 [Information] Response: 221 Goodbye.

以及负责连接的代码：

 private void InitializeFtpConnection(FtpClient _ftpClient)
    {
        if (!_ftpClient.IsConnected)
        {
            _ftpClient.EncryptionMode = FtpEncryptionMode.Explicit;
            _ftpClient.SslProtocols = SslProtocols.Tls12;
            _ftpClient.DataConnectionType = FtpDataConnectionType.PASV;
            _ftpClient.RetryAttempts = 10;
            _ftpClient.OnLogEvent = OnFTPLogEvent;
            _ftpClient.ValidateCertificate += new FtpSslValidation(OnValidateCertificate);

            _ftpClient.Connect();              
        }
    }

    //method called from service
    private byte[] TryGetFile(string filename, FileStorageLocation fromLocation)
    {
        byte[] fileDownload = null;

        for (int i = 1; i <= retryCount; i++)
        {
            using (var _ftpClient = new FtpClient(_activeAddress, _username, _password))
            {
                try
                {
                    InitializeFtpConnection(_ftpClient);
                    _ftpClient.Download(out fileDownload, $"{GetBaseUrl(fromLocation)}/{filename}");
                    return fileDownload;
                }
                catch (Exception e)
                {
                    if (i == retryCount)
                    {
                        throw new Exception("Failed downloading a file from the FTP server.", e);
                    }
                }
            }
        }
        return null;
    }

更新：它在充当 FTP 的 azure app 服务上。

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1 回答 1

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发布我如何缓解此问题的答案。根据这个线程https://social.msdn.microsoft.com/Forums/en-US/61532ef2-d3d8-4151-bcdf-c4c2dc144197/is-there-an-ftp-connection-limit-to-azure-web- apps?forum=windowsazurewebsitespreview，Azure App Service Ftp 限制为每秒 3 个连接，并且由于 FTP 需要为每个操作建立新连接，我们超出了此限制，因此出现用户无法登录的错误。添加 Polly 和重试模式，通常在第二个之后尝试应用重新连接并继续执行任务。这是一些示例代码：

 private Polly.Retry.RetryPolicy retryPolicy;

    public FtpServerDocumentReader()
    {
        

        retryPolicy = Policy.Handle<Exception>().WaitAndRetry(5,retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),
                    onRetry: (response, calculatedWaitDuration) =>
                    {
                        logger.LogWarning($"Failed attempt. Waited for {calculatedWaitDuration}. Retrying. {response.Message} - {response.StackTrace}");
                    });
    }
   private void InitializeFtpConnection(FtpClient _ftpClient)
        {
            if (!_ftpClient.IsConnected)
            {
                _ftpClient.EncryptionMode = FtpEncryptionMode.Explicit;
                _ftpClient.SslProtocols = SslProtocols.Tls12;
                _ftpClient.DataConnectionType = FtpDataConnectionType.PASV;
                _ftpClient.RetryAttempts = 10;
                _ftpClient.OnLogEvent = OnFTPLogEvent;
                _ftpClient.ValidateCertificate += new FtpSslValidation(OnValidateCertificate);

                retryPolicy.Execute(() =>
                {
                    _ftpClient.Connect();
                });
            }
        }
   private void UploadFile(string filename, byte[] file, FileStorageLocation toLocation = FileStorageLocation.Archive)
        {
            FtpStatus result = new FtpStatus();

            using (var _ftpClient = new FtpClient(_activeAddress, _username, _password))
            {
                try
                {
                    InitializeFtpConnection(_ftpClient);
                    result = _ftpClient.Upload(file, $"{GetBaseUrl(toLocation)}/{filename}");
                    if (result == FtpStatus.Success)
                    {
                        _logger.LogInformation($"File {filename} uploaded to {toLocation} on FTP server");
                    }
                }
                catch (Exception e)
                {
                    _logger.LogError(e, $"Failed uploading a file to the server. Filename: {filename}, username: {_username}, server: {_archiveAddress}");
                }
            }
        }
于 2021-12-02T22:08:42.090 回答