Logging in ASP.NET Core
💡 Concept Name
Logging in ASP.NET Core
📘 Quick Intro
Logging in ASP.NET Core allows you to track application behavior and errors using built-in or third-party providers. It's fully integrated and supports structured logging, configuration via appsettings.json, and scopes.
🧠 Analogy / Short Story
Imagine flying an airplane without any dashboard indicators. That’s a system without logging. Logs are like your dashboard—showing you the altitude, fuel, and alerts so you can act quickly. In web apps, logs tell you what’s happening under the hood.
🔧 Technical Explanation
ASP.NET Core uses ILogger interface from Microsoft.Extensions.Logging. The system supports multiple logging providers like Console, Debug, EventSource, Application Insights, and more. You can configure log levels in appsettings.json or programmatically.
Structured logging (like Serilog) enhances this further with output formatting, sinks, and JSON logging for observability tools.
🎯 Purpose & Use Case
- ✅ Debug issues and exceptions
- ✅ Monitor application health
- ✅ Track user actions or system events
- ✅ Integrate with third-party tools like Seq, Kibana, or Splunk
- ✅ Set up custom logging per environment
💻 Real Code Example
Example: Logging setup in Program.cs
var builder = WebApplication.CreateBuilder(args);
builder.Logging.ClearProviders();
builder.Logging.AddConsole();
builder.Logging.AddDebug();
var app = builder.Build();
app.MapGet("/", (ILogger<Program> logger) => {
logger.LogInformation("Hello logged at {time}", DateTime.UtcNow);
return "Hello Logging!";
});
app.Run();
Configuration in appsettings.json:
"Logging": {
"LogLevel": {
"Default": "Information",
"Microsoft": "Warning",
"Microsoft.Hosting.Lifetime": "Information"
}
}
❓ Interview Q&A
Q1: What is the use of ILogger in ASP.NET Core?
A: It’s used for logging messages to different providers like Console, Debug, etc.
Q2: How do you add a logging provider?
A: Using methods like AddConsole(), AddDebug() in Program.cs.
Q3: Where is logging configuration done?
A: In appsettings.json or Program.cs.
Q4: What is the purpose of ClearProviders()?
A: It removes the default logging providers to let you add only the ones you need.
Q5: Name some popular third-party logging libraries?
A: Serilog, NLog, Log4Net.
Q6: Can logs be filtered based on levels?
A: Yes. Levels like Information, Warning, Error, etc., can be configured per namespace.
Q7: Is logging asynchronous?
A: By default, most built-in providers are synchronous. Third-party providers may offer async logging.
Q8: How to log exception stack trace?
A: Use logger.LogError(ex, "message").
Q9: What are scopes in logging?
A: Used to group logs for a single operation or request.
Q10: Can logs be written to a database?
A: Yes, using providers like Serilog with SQL sinks.
📝 MCQs
📝 MCQs
Q1. Which interface is used for logging in ASP.NET Core?
- ILogger
- ILog
- LoggerService
- ILoggerFactory
Q2. Which provider logs to the command line?
- Debug
- Console
- Trace
- ApplicationInsights
Q3. Where do you configure log levels?
- Startup.cs
- Program.cs
- appsettings.json
- launchSettings.json
Q4. Which logging library supports sinks and structured logging?
- Log4Net
- NLog
- Serilog
- Console
Q5. What does ClearProviders() do?
- Adds all providers
- Resets logging
- Removes all default logging providers
- Flushes logs
Q6. Can you filter logs by category?
- No
- Yes
- Only in Debug mode
- Only in Release mode
Q7. What is the purpose of scopes in logging?
- Change logging level
- Enable async logging
- Send to DB
- Group logs by request or operation
Q8. Which method logs an error with stack trace?
- WriteLog()
- LogInfo()
- LogError(ex, message)
- Debug.Write()
Q9. Which package is required for Serilog?
- Serilog.Base
- Serilog.Core
- Serilog.AspNetCore
- Microsoft.Extensions.Logging
Q10. Which log level represents detailed debug info?
- Error
- Warning
- Trace
- Info
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