Amazon CloudWatch Logs and .NET Logging Frameworks

You can use Amazon CloudWatch Logs to monitor, store, and access your application’s logs. To get log data into CloudWatch Logs, you can use an AWS SDK or install the CloudWatch Log agent to monitor certain log folders. Today, we’ve made it even easier to use CloudWatch Logs with .NET applications by integrating CloudWatch Logs with several popular .NET logging frameworks.

The supported .NET logging frameworks are NLog, Log4net, and the new built-in ASP.NET Core logging framework. For each framework, all you need to do is add the appropriate NuGet package, add CloudWatch Logs as an output source, and then use your logging library as you normally would.

For example to use CloudWatch Logs with a .NET application using NLog, add the AWS.Logger.NLog NuGet package, and then add the AWS target into your NLog.config file. Here is an example of an NLog.config file that enables both CloudWatch Logs and the console as output for the log messages.

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      throwExceptions="true">
  <targets>
    <target name="aws" type="AWSTarget" logGroup="NLog.ConfigExample" region="us-east-1"/>
    <target name="logfile" xsi:type="Console" layout="${callsite} ${message}" />
  </targets>
  <rules>
    <logger name="*" minlevel="Info" writeTo="logfile,aws" />
  </rules>
</nlog>

After performing these steps, when you run your application the log messages written with NLog will be sent to CloudWatch Logs. Then you can view your application’s log messages in near real time from the CloudWatch Logs console. You can also set up metrics and alarms from the CloudWatch Logs console, based on your application’s log messages.

These logging plugins are all built on top of the AWS SDK for .NET, and use the same behavior used by the SDK to find AWS credentials. The credentials used by the logging plugins must have the following permissions to access CloudWatch Logs.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "logs:CreateLogGroup",
        "logs:CreateLogStream",
        "logs:PutLogEvents",
        "logs:DescribeLogGroups"
      ],
      "Resource": [
        "arn:aws:logs:*:*:*"
      ]
    }
  ]
}

For .NET Lambda functions it is recommended to not use these packages because they batch logging messages in a queue and send messages to CloudWatch Logs using a background thread. The use of the background thread means that the messages are not guaranteed to be delivered when used in AWS Lambda. The reason is because the background thread will be frozen once a Lambda event is processed and may not ever be unfrozen if more Lambda events are not received for some time.

When using Lambda it is recommended to use either the ILambdaContext.Logger.LogLine or the Amazon.Lambda.Logging.AspNetCore package.

The AWS .NET logging plugins are a new open source project on GitHub. All of the plugins are there, including samples and instructions on how to configure CloudWatch Logs for each of the supported .NET logging frameworks.

For any comments or issues for the new libraries, open an issue in the GitHub repository.