Order of Settings Precedence for .NET Applications

The post Flexible Leveraging of appsettings.json in .NET Applications examined how to utilize appsettings.json files for storing and loading settings under various conditions.

The post Setting the Staging & Production Environments During Development examined how to leverage the active environment to control settings.

The post Overriding appsettings.json via Command Line looked at how to override settings via command line arguments.

And finally, the post Overriding appsettings.json via Environment Variables looked at how to override settings via environment variables.

The question arises - what if you use all of these at once? Which will take precedence?

For the files, it will depend on how you have written your code.

If you don’t do anything at all in the startup, the precedence will be as follows:

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

If your startup is like this:

using ApplicationSettings.Properties;
using Microsoft.Extensions.Options;

var builder = WebApplication.CreateBuilder(args);

// Check if we are running in development
if (builder.Environment.IsDevelopment())
{
    // Load optional developer-specific settings
    builder.Configuration.AddJsonFile($"appsettings.{Environment.MachineName}.json", optional: true);
}

// Configure options DI
builder.Services.AddOptions<SystemSettings>()
    .Bind(builder.Configuration.GetSection(nameof(SystemSettings)));

var app = builder.Build();

app.MapGet("/", (IOptions<SystemSettings> options) =>
{
    var settings = options.Value;
    return settings;
});

app.Run();

The precedence will be as follows:

Development Environment

1. appsettings.json
2. appsettings.Development.json
3. appsettings.{Machine Name}.json

Staging / Production Environment

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

We can verify this empirically.

Our appsettings.json is as follows:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "SystemSettings": {
    "ForegroundColour": "White",
    "BackgroundColour": "Black"
  }
}

In the terminal, we set the environment variables as follows:

export SystemSettings__ForegroundColour=Neon
export SystemSettings__BackgroundColour=Mauve

And finally, we run our application like this:

dotnet run --SystemSettings:ForegroundColour=Maroon --SystemSettings:BackgroundColour=Pink

You will see the following:

The order is thus as follows:

1. appsettings.json (and all its descendants)
2. Environment Variables
3. Command Line Arguments

TLDR

Settings are loaded in the following order: appsettings.json, then environment variables, and finally command-line arguments.

The code is in my GitHub.

Happy hacking!