Why ILogger File Logging Fails in Production (and How to Fix It)

Many .NET developers face a confusing issue:

Logging to file works perfectly in Development,
but no log file is created in Production.

This problem appears so often that it’s easy to think it’s a bug in .NET or ILogger.
In reality, it’s a misunderstanding of how logging works in ASP.NET Core.

In this article, we’ll explain:

• Why this happens
• What ILogger actually does (and doesn’t)
• The most common production pitfalls
• A correct, production-ready file logging setup

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1. ILogger Does NOT Support File Logging

The first and most important fact:

Microsoft.Extensions.Logging has no built-in file logger

ILogger is just an abstraction.
It forwards logs to providers, such as:

• Console
• Debug
• EventSource
• Third-party providers (Serilog, NLog, etc.)

So this will never create a file by itself:

ILogger<MyService> logger;
logger.LogInformation("Hello World");

If file logging “worked” in Development, it was because:

• You added a provider indirectly
• Or your IDE showed Debug output
• Or configuration was loaded only in Development

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2. Why It Works in Development but Fails in Production

Here are the real reasons behind the issue.

Reason 1: Logging configured only in appsettings.Development.json

ASP.NET loads configuration in this order:

1. appsettings.json
2. appsettings.{Environment}.json
3. Environment variables

If file logging is configured only in:

appsettings.Development.json

Then in Production:

• That config is never loaded
• File logging simply doesn’t exist

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Reason 2: Log directory does not exist

ASP.NET does not create directories automatically.

If you configure:

"path": "Logs/app.log"

But /Logs does not exist → no file is created

No exception. No warning. Just silence.

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Reason 3: Missing write permissions (MOST COMMON)

In Production, your app usually runs as:

• IIS App Pool identity
• Docker container user
• Linux service account

That user often cannot write to disk.

So file creation fails silently.

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3. The Correct Way: Use a Real File Logger (Serilog)

Let’s fix everything properly.

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4. Install Required Packages

dotnet add package Serilog.AspNetCore
dotnet add package Serilog.Sinks.File

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5. Configure Serilog in Program.cs

using Serilog;

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseSerilog((context, services, configuration) =>
{
    configuration
        .ReadFrom.Configuration(context.Configuration)
        .Enrich.FromLogContext();
});

var app = builder.Build();

app.MapGet("/", (ILogger<Program> logger) =>
{
    logger.LogInformation("Application started successfully");
    return "Hello World";
});

app.Run();

---

6. Configure Logging in appsettings.json (NOT Development-only)

{
  "Serilog": {
    "Using": [ "Serilog.Sinks.File" ],
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft": "Warning",
        "System": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "Logs/app-.log",
          "rollingInterval": "Day",
          "shared": true
        }
      }
    ]
  }
}

This configuration works in Development AND Production

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7. Ensure the Log Folder Exists

Create it manually:

/Logs

Or programmatically:

Directory.CreateDirectory("Logs");

Best practice: create it before logging starts

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8. Fix Production Permissions

IIS

Grant write access to:

IIS AppPool\YourAppPoolName

Linux

chmod -R 755 Logs
chown -R appuser:appuser Logs

Docker

Mount a writable volume:

volumes:
  - ./Logs:/app/Logs

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9. Final Checklist (Production Safe)

Before blaming .NET, check this list:

• Using Serilog / NLog
• Logging config in appsettings.json
• Log directory exists
• App has write permissions
• Not relying on Debug output

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Conclusion

ILogger is not broken in Production.
It simply does exactly what it’s designed to do — nothing more.

File logging failures are almost always caused by:

• Missing providers
• Wrong configuration scope
• File system permissions

Once you understand this, logging becomes predictable, stable, and production-safe.

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I’m Morteza Jangjoo and “Explaining things I wish someone had explained to me”