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Learn how to effectively configure `Serilog` for structured logging in ASP.NET Core while including essential source context information formatted as JSON.
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Mastering Serilog with a Custom Template and JSON Formatter in ASP.NET Core

Logging is an essential feature in any application, especially web applications built on frameworks like ASP.NET Core. One of the most powerful logging libraries available is Serilog, which allows for structured logging, making it easier to track down issues and understand application behavior. A common challenge developers face when using Serilog is how to customize logging templates while still utilizing JSON formatting. In this guide, we will address these concerns and provide a clear solution.

The Problem: Custom Template and JSON Formatting Conflict

When using Serilog with ASP.NET Core, particularly version 2.1, developers often want to include elements like {SourceContext} in their log output. However, there is a known limitation where you cannot specify both an outputTemplate and a formatter simultaneously. This creates confusion and frustration, especially in scenarios where structured logging is desired.

The Specific Issue

You may have attempted to configure Serilog in your appsettings.json like this:

[[See Video to Reveal this Text or Code Snippet]]

This would lead to conflicts, preventing the desired log output from being generated properly.

The Solution: Updated Configuration for Serilog

Good news! Changes have occurred in the Serilog library, and newer versions now handle this configuration conflict more gracefully, especially if you are working with Serilog.AspNetCore version 3.4.0 on ASP.NET Core 5.

Key Configuration Steps

To resolve the issue, you can maintain the structured logging feature while avoiding the conflict between outputTemplate and formatter. Here’s how you can do it:

Remove the Output Template: Instead of trying to combine both settings, simply remove the outputTemplate definition from your configuration.

Use the JSON Formatter: Keep the formatter setting for compact JSON output, which will allow you to still capture valuable log data in a structured format.

Here’s an example of how the updated configuration should look in your appsettings.json file:

[[See Video to Reveal this Text or Code Snippet]]

Resulting Log Variables

Using this updated configuration, you will benefit from receiving essential log variables such as:

@ t: The timestamp of the log entry.

@ mt: Message template used for the log entry.

@ l: Log level (excluding for default information level).

SourceContext: The context in which the logging occurred.

It is important to note that the variable @ l will not be shown if the log level is Information, as it is considered the default.

Conclusion

By understanding the configuration conflicts and adapting to Serilog’s capabilities in newer versions, you can successfully achieve customized logging templates along with structured JSON outputs. This configuration will enhance your application's logging strategy, making it more robust and insightful. Remember, adapting to changes in libraries like Serilog is crucial for making the most out of your logging experiences in ASP.NET Core.

For more information on how to implement logging in your applications effectively, consider exploring additional features of Serilog and other available formats for logging!