Azure and .NET nested JSON sections. Did you know?

.NET Core (and ASP.NET Core) supports (hierarchical configuration data)¹, which is represented by nesting JSON sections.

Let's look at this JSON configuration file:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet"
  },
  "SecretSettings": {
    "SqlConnectionString": "Sql connection string",
    "BlobConnectionString": "Blob connection string"
  }
}

We have variables nested within sections of the JSON. i.e.: SecretSettings:SqlConnectionString.

When .NET reads this information, it uses the Configuration Providers hooked up as middlewares, i.e.:

var config = new ConfigurationBuilder()
  .SetBasePath(appDirectory)
  .AddJsonFile(Path.Combine(appDirectory, "settings.json"), optional: true, reloadOnChange: true) // config provider
  .AddEnvironmentVariables() // config provider
  .Build();

The Configuration API then reads the hierarchical configuration data by flattening it with the use of a delimiter in the configuration keys. The delimiters can be either : (colon) or __ (double underscore).

Did you know that depending on the underlying platform you need to specify the correct delimiter?

If you are on a Linux app service or container, you must use __, but if you are on the Windows platform you can use either __ or :. This is used as environment variables loaded when running apps.

Microsoft says the same in this article

In a default Linux app service or a custom Linux container, any nested JSON key structure in the app setting name like ApplicationInsights:InstrumentationKey needs to be configured in App Service as ApplicationInsights__InstrumentationKey for the key name. In other words, any : should be replaced by __ (double underscore).