Semantic Logging In Akka.NET: A Feature Enhancement

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Semantic Logging Support in Akka.NET: A Detailed Enhancement

In the realm of modern application development, logging plays a pivotal role in monitoring, debugging, and maintaining the health of systems. For Akka.NET, a powerful toolkit for building concurrent and distributed applications, enhancing the existing logging capabilities with native semantic logging support is a significant leap forward. Let's dive into the proposal for adding default semantic logging support to Akka.NET, addressing the current problems, desired solutions, and design considerations.

The Case for Semantic Logging

Current Challenges

Currently, Akka.NET users who wish to employ semantic or structured logging—akin to what's offered by Serilog and Microsoft.Extensions.Logging (MEL)—encounter friction. The primary pain point is that the intuitive, property-named syntax (e.g., Logger.Info("OnCreateBet BetId:{BetId} created", BetId);) doesn't play well with Akka.NET's EventFilter during tests. Instead, developers are forced to resort to older, positional formatting (e.g., Logger.Info("OnCreateBet BetId:{0} created", BetId);), which is less readable and maintainable.

To illustrate, consider the scenario where a developer wants to verify that a specific log message is emitted when a CreateBet event occurs. Using the desired semantic syntax, the EventFilter might fail, whereas the positional syntax would work. This inconsistency necessitates workarounds and reduces the overall developer experience.

The crux of the issue lies in the fact that while Akka.NET's infrastructure has been prepared for semantic logging (as noted in related issues like #5135), a default semantic logging formatter that works out-of-the-box—without requiring plugin-specific code—is still missing.

Addressing the Problem

The goal is to enable Akka.NET to natively support semantic logging, so developers can leverage {PropertyName} template syntax by default. This means that using standard Context.GetLogger() should seamlessly integrate with semantic logging conventions familiar to users of MEL, Serilog, and NLog. The essence is to allow developers to write expressive log messages that capture the intent and context of the logged event.

Proposed Solution: Native Semantic Logging Support

The core of the solution involves several key components:

  1. Default {PropertyName} Template Syntax Support: Implement support for {PropertyName} template syntax out-of-the-box. This removes the need for provider-specific APIs when using the standard Context.GetLogger(). The aim is to align with established conventions from MEL, Serilog, and NLog, making it easier for developers to adopt and use semantic logging.
  2. Storing Template and Properties in LogEvent: Enhance the LogEvent class to store both the template and properties of the log message. For instance, if the log message is "OnCreateBet BetId:{BetId} created", the template would be the entire string, and the properties would be a dictionary containing {"BetId": "12345"}. The formatted message, "OnCreateBet BetId:12345 created", would also be stored for backward compatibility.
  3. Updating EventFilter: Modify the EventFilter to match against both the semantic templates and the formatted strings. This ensures that tests can accurately verify log messages using either the template pattern or the traditional formatted string. Backward compatibility with existing {0} format tests must be maintained.
  4. Maintaining Backward Compatibility: Ensure that existing {0} style formatting continues to work and that existing EventFilter tests don't break. The changes should be non-breaking API-wise, allowing existing Akka.NET applications to adopt semantic logging without requiring significant code modifications.

Design Choices and Considerations

Leveraging Microsoft.Extensions.Logging (MEL)

One of the primary design considerations is whether to leverage existing .NET libraries or build a custom parser. The recommended approach is to leverage Microsoft.Extensions.Logging (MEL). MEL already provides battle-tested template parsing for {PropertyName} syntax and integrates seamlessly with the .NET ecosystem. By reusing existing infrastructure, the development effort is reduced, and the solution benefits from the robustness and maturity of MEL.

Alternatively, building a custom parser would offer more control but would also entail a higher maintenance burden. It would require replicating the template parsing logic already present in Serilog and MEL. This approach is generally less desirable unless there are specific constraints or requirements that MEL cannot satisfy.

Key Questions and Considerations

Several key questions arise when designing the solution:

  • Should we support both {PropertyName} and {0} syntax simultaneously? The answer is yes. Maintaining backward compatibility is crucial, so existing {0} syntax should continue to work alongside the new {PropertyName} syntax.
  • Should we build our own parser or leverage MEL's infrastructure? As mentioned, leveraging MEL's infrastructure is the preferred approach due to its robustness and integration with the .NET ecosystem.
  • How do provider-specific implementations (Serilog, NLog) interact with this? The default implementation should work without requiring plugins. Serilog, NLog, and MEL adapters can then provide enhanced formatting if needed, without breaking existing provider implementations.
  • What's the role of ILogMessageFormatter from #5135 in this solution? The ILogMessageFormatter can be used to provide custom formatting logic for specific log messages or properties. It allows developers to extend the default formatting behavior without modifying the core Akka.NET code.

Implementation Outline

To illustrate the proposed changes, consider the following implementation sketch:

Extending LogEvent

The LogEvent class would be extended to include the message template and properties:

public class LogEvent
{
    public string Message { get; } // Formatted message (backwards compat)
    public string? MessageTemplate { get; } // Semantic template
    public IReadOnlyDictionary<string, object>? Properties { get; } // Structured data
    public bool IsSemanticLog => MessageTemplate != null;
}

Updating EventFilter

The EventFilter would be updated to match against both the message template and the formatted message:

internal bool Matches(LogEvent logEvent)
{
    // Try template matching first (semantic logs)
    if (logEvent.MessageTemplate != null && MatchesPattern(logEvent.MessageTemplate))
        return true;
        
    // Fall back to formatted message (backwards compat)
    return MatchesPattern(logEvent.Message);
}

Provider Integration

The default implementation would work seamlessly without plugins. Serilog, NLog, and MEL adapters can provide enhanced formatting, ensuring no breaking changes to existing provider implementations.

Benefits of Semantic Logging

Adopting native semantic logging in Akka.NET brings several benefits:

  • Alignment with Modern .NET Logging Practices: Semantic logging aligns Akka.NET with modern .NET logging practices, making it easier for developers familiar with MEL, Serilog, and NLog to adopt and use Akka.NET.
  • Improved Structured Logging: Semantic logging enables better structured logging in production environments. Structured logs are easier to query, analyze, and visualize, providing valuable insights into the behavior of Akka.NET applications.
  • Resolution of EventFilter Limitations: The current limitations of EventFilter in tests are resolved, allowing developers to write more accurate and reliable tests.
  • Backward Compatibility: The changes are designed to be backward-compatible, ensuring that existing Akka.NET applications can adopt semantic logging without significant code modifications.
  • Foundation for Future Enhancements: Semantic logging provides a foundation for future enhancements, such as log enrichment and correlation.

Future Possibilities

This enhancement also lays the groundwork for several related features:

  • ILoggingAdapter.WithPrefix() with semantic context: This allows adding contextual information to log messages, making it easier to trace the flow of events through the system. Imagine being able to automatically include the actor's name or ID in every log message, providing instant context without having to manually add it each time.
  • Adding SpanId/ActivityId to LogEvent: This enables distributed tracing, making it easier to diagnose performance issues and understand the interactions between different services. By including these IDs, you can trace a single request as it moves through multiple actors and services, identifying bottlenecks and points of failure.
  • Future log enrichment scenarios: Support for dynamically adding extra information to log entries based on the current context. Think of being able to automatically add the user's ID or the current transaction ID to log messages when they occur within a specific scope.

In conclusion, the addition of default semantic logging support to Akka.NET represents a significant improvement in the toolkit's capabilities. By aligning with modern .NET logging practices, resolving existing limitations, and laying the foundation for future enhancements, this feature will greatly benefit Akka.NET developers.