How to override ASP.NET Core configuration array settings using environment variables

Question

TL;DR

In an ASP.NET Core app, I have an appsettings.json config file which uses a JSON array to configure a collection of settings.

How do I override a setting of one of the array objects using environment variables?

Background

I'm using Serilog in an ASP.NET Core application and using the Serilog.Settings.Configuration, to allow it to be configured using appsettings.json.

The configuration is like this:

{
  "Serilog": {
    "Using":  ["Serilog.Sinks.Literate"],
    "MinimumLevel": "Debug",
    "WriteTo": [
      { "Name": "File", "Args": { "path": "%TEMP%\\Logs\\serilog-configuration-sample.txt" } }
    ],
    "Enrich": ["FromLogContext", "WithMachineName", "WithThreadId"],
    "Properties": {
        "Application": "Sample"
    }
  }
}

When deployed, I want to override some of the settings, e.g. the MinimumLevel, and the path to the log file. My preferred option is to do this via environment variables as I'm deploying to an Azure App Service, so I'll use the App settings through the Azure management portal (these are realised as environment variables).

I can easily set the MinimumLevel by adding an environment variable with the name: Serilog:MinimumLevel and the application name Serilog:Properties:Application.

What is the format for specifying a setting with an array?

Solution

After looking at the configuration in the debugger I found the answer.

• Serilog__WriteTo__0__Args__path (All platforms)
• Serilog:WriteTo:0:Args:path (Windows)
• Serilog--WriteTo--0--Args--path (sourced From Azure Key Vault)

Note: The Configuration in ASP.NET Core documentation now covers this.

So I need to use the array index (zero-based) as if it were a name.

Here is the screenshot of the debugger, also (thanks to Victor Hurdugaci in the comments), the unit tests are a good place to look for examples.

Comments

[Dumitru]

I had the same problem - I could not stand the magic of names, colons and array indexes (Serilog:WriteTo:0:Args:path) and couple of months ago I wrote a new configuration provider to make this kind of configuration easier - github.com/dsbenghe/NotMicrosoft.Configuration

[Victor Hurdugaci]

The tests are another great place to look for examples: github.com/aspnet/Configuration/blob/dev/test/…

[Jaanus Varus]

@VictorHurdugaci Link is dead. Here's an updated one: github.com/aspnet/Configuration/blob/…

[Jaanus Varus]

@JamesSkimming Ah right, I only checked the link in the comment :)

[halllo]

If you use this environment variable in a unix system, you have to replace the : with __: Serilog__WriteTo__0__Args__path

[Nate Zaugg]

The now documentation suggests always using the __ form over the : form, even on Windows.

[James Skimming]

@Jacob, you should ask that as a new question. It's outside the scope of this question and, there may be several answers which could be worth expanding upon.