How to use a fallback when it cannot send data to CloudWatch

[thewinner55]

In cases where sending to CloudWatch fails under any circumstances, write to a log file instead.
Remark : I tried inputting an incorrect config value, but it did not go into the catch block.

Thank a lot.

public class CloudWatchLogger
{
    public CloudWatchLogger(CloudWatchLoggerReq req)
    {
        // Setup the NLog configuration
        var config = new LoggingConfiguration();

        // Add console target
        config.AddRule(LogLevel.Trace, LogLevel.Fatal, new ConsoleTarget());

        var awsTarget = new AWSTarget()
        {
            LogGroup = req.LogGroupName,
            // (Optional) How often batches of log messages should be pushed to AWS CloudWatch
            BatchPushInterval = TimeSpan.FromSeconds(3),
            FlushTimeout = TimeSpan.FromSeconds(req.TimeoutSec),

            // (Optional) Whether NLog should try create the log group if it does not exist or not
            DisableLogGroupCreation = true,

            // (Optional) The maximum number of log events that are kept in memory before being pushed to
            // AWS CloudWatch
            MaxQueuedMessages = 10000,

            // (Optional) A string to prefix log stream names with
            LogStreamNamePrefix = "Prefix",

            // (Optional) A string to suffix log stream names with
            LogStreamNameSuffix = "Suffix",

            // (Optional) AWS credentials that should be used to log into AWS and access AWS CloudWatch
            Credentials = new BasicAWSCredentials(req.Accesskey, req.SecretAccessKey),

            // CloudWatch logs should be logged in. In this case it defaults to the AWS Profile's region
            Region = req.Region,

            // (Optional) Custom layout that should be used when formatting log messages
            Layout = new SimpleLayout("${message}"),
            LogStreamName = "${date:format=yyyyMMdd}",

            // (Optional) Log System Error
            //LibraryLogFileName = $"{req.PathFileLog}/Logs/aws-logger-erros.txt",          
        };

        // Add AWS target and fallback file target
        config.AddRule(LogLevel.Trace, LogLevel.Fatal, awsTarget);

        // Add file target for fallback
        var fileTarget = new FileTarget("file")
        {
            FileName = $"{req.PathFileLog}/Logs/Log_${{date:format=yyyyMMdd}}.txt", // Path สำหรับบันทึกไฟล์ log
            Layout = new SimpleLayout("[${date}] ${message} ${exception}")
        };
        config.AddRule(LogLevel.Error, LogLevel.Fatal, fileTarget);

        LogManager.Configuration = config;
    }

    //create logMessage
    public static void LogMessageAsync(SendMessageCloudWatch req)
    {
        var log = LogManager.GetCurrentClassLogger();
        string msg = string.Empty;
        try
        {
            msg = req.msg;
            log.Trace(msg);
        }
        catch (Exception ex)
        {
            //Failed to send log to AWS CloudWatch
            string guid = System.Guid.NewGuid().ToString();
            log.Error($"Req - {guid}: {msg}");
            log.Error($"Res - {guid}: {ex}");
        }
    }
}