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

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?

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.