Logging Exercises

Logging - Practice Exercises

Practice structured logging for production-grade .NET services.

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Foundations

Exercise 1: Structured Logging Basics

Q: Log a trade event using structured logging.

A:

_logger.LogInformation("Trade executed {TradeId} {Symbol} {Quantity}", trade.Id, trade.Symbol, trade.Quantity);

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Exercise 2: Log Levels

Q: When do you use Debug vs Information vs Warning?

A: Debug for developer diagnostics, Information for normal business events, Warning for unusual but handled conditions.

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Exercise 3: Correlation IDs

Q: Attach a correlation ID to all logs in a request.

A: Use middleware to set a scope with the correlation ID.

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Exercise 4: Log Scopes

Q: Use BeginScope to include request context.

A:

using (_logger.BeginScope(new Dictionary<string, object> { ["CorrelationId"] = cid }))
{
    _logger.LogInformation("Processing request");
}

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Exercise 5: Avoid Logging PII

Q: Identify PII and prevent it from being logged.

A: Redact names, emails, tokens, and account numbers; log hashes or partial values.

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Exercise 6: Request Logging Middleware

Q: Log incoming requests with path, method, and latency.

A: Use middleware to time and log the request before and after the next delegate.

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Exercise 7: Exception Logging

Q: Log an exception with relevant context.

A:

_logger.LogError(ex, "Order {OrderId} failed for {Symbol}", orderId, symbol);

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Exercise 8: Message Templates

Q: Why should you avoid string interpolation in log messages?

A: Templates allow structured fields and defer formatting until needed.

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Exercise 9: ILogger Injection

Q: Inject and use a typed logger in a handler.

A:

public class PlaceOrderHandler
{
    private readonly ILogger<PlaceOrderHandler> _logger;
}

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Exercise 10: Configure Providers

Q: Configure console and JSON logging in ASP.NET Core.

A: Use AddConsole() and a JSON formatter or Serilog for structured sinks.

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Intermediate

Exercise 11: Serilog File Sink

Q: Configure Serilog to write JSON logs to a file.

A:

Log.Logger = new LoggerConfiguration()
    .WriteTo.File(new JsonFormatter(), "logs/app.json")
    .CreateLogger();

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Exercise 12: Enrichers

Q: Add machine name and environment to each log.

A: Use Serilog enrichers or custom scope properties.

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Exercise 13: Sampling

Q: Reduce log volume for high-frequency debug events.

A: Apply sampling filters or log only every Nth event.

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Exercise 14: Aggregation Pipelines

Q: Why send logs to a centralized system?

A: Centralized logs enable search, correlation, and retention policies across services.

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Exercise 15: Distributed Tracing Context

Q: Include trace/span IDs in logs.

A: Enrich logs with Activity.Current.TraceId and SpanId.

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Exercise 16: EventId Usage

Q: Use EventId for stable log classification.

A:

_logger.LogWarning(new EventId(2001, "RiskLimit"), "Risk limit reached");

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Exercise 17: Avoid Expensive Formatting

Q: Log only when level is enabled.

A:

if (_logger.IsEnabled(LogLevel.Debug))
    _logger.LogDebug("Payload: {Payload}", Serialize(payload));

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Exercise 18: HTTP Body Logging

Q: When is it safe to log request/response bodies?

A: Only for non-sensitive data and in non-production or sampled paths.

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Exercise 19: Background Service Logging

Q: Add structured logs around a scheduled job.

A: Log job start, duration, and items processed with metrics-like fields.

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Exercise 20: Domain Event Logging

Q: Log domain events without leaking internal state.

A: Log identifiers and summaries, not full objects or secrets.

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Advanced

Exercise 21: Correlation Across Queues

Q: Propagate correlation IDs across message queues.

A: Include correlation ID in message headers and restore it into logging scopes.

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Exercise 22: Redaction and Masking

Q: Implement masking for account numbers.

A:

string Mask(string value) => value.Length <= 4 ? "****" : $"****{value[^4..]}";

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Exercise 23: Logs vs Metrics

Q: When should you emit a metric instead of a log?

A: Use metrics for high-frequency counters and latency percentiles.

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Exercise 24: Logging Failures

Q: What happens if a logging sink fails?

A: Use async/buffered sinks and avoid crashing the app on logging errors.

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Exercise 25: High-Throughput Logging

Q: How do you minimize logging overhead in hot paths?

A: Use minimal log levels, sampling, and avoid allocations in message construction.

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Exercise 26: Retention Policies

Q: Define a retention strategy for logs.

A: Retain high-value audit logs longer and rotate verbose logs faster.

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Exercise 27: Compliance Considerations

Q: What logging considerations exist for regulated domains?

A: PII redaction, audit trails, tamper resistance, and controlled access.

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Exercise 28: OpenTelemetry Logging

Q: Export logs using OpenTelemetry.

A: Configure OTel logging provider and export to your collector.

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Exercise 29: Testing Logs

Q: Assert that a handler writes a warning log.

A: Use a test logger or capture logs via ILoggerProvider.

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Exercise 30: Log Schema Design

Q: Define common fields for log consistency.

A: Use fields like correlation_id, service, environment, event, and duration_ms.