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}");
        }
    }
}

[ashishdhingra]

@thewinner55 Thanks for starting discussion. I see some problem in your code. You are defining static method LogMessageAsync(), but your constructor is not static, which means it only executes when you create an instance of your custom CloudWatchLogger class.

Also note that in NLog.AWS.Logger.AWSTarget class, it:

• Exposes LibraryLogErrors (default value true) and LibraryLogFileName (default value aws-logger-errors.txt)
• These properties are used when there is an issue sending logs (e.g. due to AWS credentials not configured)
• Delegate AwsLogLibraryAlert is also set, which calls NLog's InternalLogger.Error().
  • To use NLog's InternalLogger, properties InternalLogger.LogFile and InternalLogger. LogLevel need to be set.

I was able to use your code (corrected and modified for reproduction):
CloudWatchLogger.cs

using Amazon.Runtime;
using NLog.Config;
using NLog.Layouts;
using NLog.Targets;
using NLog;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NLog.AWS.Logger;

namespace NLogTestNet8
{
    public class CloudWatchLogger
    {
        static CloudWatchLogger()
        {
            // Setup the NLog configuration
            var config = new LoggingConfiguration();

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

            var awsTarget = new AWSTarget()
            {
                LogGroup = "TestCloudWatchLoggerLogGroup",
                // (Optional) How often batches of log messages should be pushed to AWS CloudWatch
                BatchPushInterval = TimeSpan.FromSeconds(3),
                FlushTimeout = TimeSpan.FromSeconds(10),

                // (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) 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-errors.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 = $"{Path.GetTempPath()}/Logs/Log_{date:format=yyyyMMdd}.txt", 
                Layout = new SimpleLayout("[${date}] ${message} ${exception}")
            };
            config.AddRule(LogLevel.Error, LogLevel.Fatal, fileTarget);

            InternalLogger.LogFile = $"{Path.GetTempPath()}/NLogInternalLogger.log";

            LogManager.Configuration = config;
        }

        //create logMessage
        public static void LogMessage(string message)
        {
            var log = LogManager.GetCurrentClassLogger();
            string msg = string.Empty;
            try
            {
                msg = message;
                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}");
            }
        }
    }
}

Program.cs

namespace NLogTestNet8
{
    internal class Program
    {
        static void Main(string[] args)
        {
            CloudWatchLogger.LogMessage("Test Message");
        }
    }
}

Executing above code:

• Created (default) aws-logger-errors.txt at the path of executing assembly and logged the error with stack trace.
• Created file <%TEMP_PATH%>\ NLogInternalLogger.log and logged similar error with stack trace.

Such exceptions are not propagated to calling (user) code since the logging is being done as part of a event loop, with logs flushed at regular configured interval (imagine web application being crashed due to just logging error, which should essentially happen in background without affecting the application).