Coding Challenge: Implement Logging in a Weather API

Objective

You are given a simple Weather API built in .NET 9.
Your task is to implement structured, configurable, and reliable logging throughout the system.

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Starter Project

The API currently exposes two endpoints:

• GET /weather/current?city=... → returns current weather.
• GET /weather/forecast?city=... → returns a 5-day forecast.

It uses a fake in-memory service to simulate weather data.
⚠️ At the moment, there is no logging at all.

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Requirements

1. Structured Logging

• Use ILogger (built-in) or integrate a logging library (e.g., Serilog, NLog).
• Each log entry should include:
  • Timestamp (UTC)
  • Log level (Information, Warning, Error, Critical)
  • Message
  • Correlation/request ID
  • Contextual data (e.g., city name for requests)
  • Assembly Version
  • Environment
  • Api name

2. Log Levels

• Information: For successful requests and system events.
• Warning: For recoverable issues (e.g., incomplete forecast data).
• Error: For failed operations (e.g., weather service unavailable).
• Critical: For unhandled exceptions.

3. Request Tracing

• Generate a correlation ID for each request.
• Include the ID in all related log entries.
• Return the correlation ID in the API response headers.

4. Error Handling

• Log unhandled exceptions.
• Return safe, user-friendly error responses (no internal stack traces).

5. Configuration

• Log level should be configurable via User-Secrets.
• Default: Console logging.
• (Optional) Add file logging or JSON output.

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Challenge Steps

1. Set up logging

   • Configure logging providers in Program.cs.

2. Add request/response logging

   • Log incoming requests (method, path, city parameter).
   • Log outgoing responses (status code, duration).

3. Add service logging

   • Log at Information when weather is successfully fetched.
   • Log at Warning for partial/missing forecast data.
   • Log at Error when the fake service fails.
   • Log at Critical for unhandled exceptions.

4. Add correlation IDs

   • Generate one per request.
   • Pass through all logs for traceability.

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Bonus Challenges

1. File or JSON Logging

   • Write logs to a file in JSON format.

2. Request Duration Metrics

   • Log duration for each request.
   • Trigger a warning if it exceeds a threshold.

3. Centralized Logging

   • Integrate with Seq, ELK, or Application Insights.

4. Log Filtering

   • Allow filtering by log level or source.

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Evaluation Criteria

• Proper use of log levels.
• Consistent correlation ID handling.
• No sensitive data in logs.
• Configurable logging (easy to change providers/levels).
• Clean, maintainable, testable code.