Access Azure App Service ConnectionString from ASP.NET Core

Question

I've got an azure app service that I've set up like this:

But when I call IConfiguration.GetConnectionString("db") I get null back.

I've read articles like this https://mderriey.com/2018/08/21/azure-app-service-connection-strings-and-asp-net-core/ which say "it just works", but they're all several years old. I assume something's changed, but what?

Enumerating over all settings in my IConfiguration object I've got no connection strings. I do in development, where my appsettings.development.json has a connectionStrings: { db: "" } defined.

I can see and read the ENV variable: POSTGRESQLCONNSTR_db from within code, and it's value is correct (what I've set via the Azure portal).

Should I expect to be able to do IConfiguration.GetConnectionString("db")? Or am I expected to switch between reading env variables in prod vs dev.

Do I need to include some nuget package to make IConfiguration work under Azure with these ENV variables and their mad prefixes?

My startup.cs basically looks like:

        public Startup(IConfiguration configuration)
        {
            this.Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

Nothing else in there of interest to this question.

Answer 1

I got confused as well, so here it is:

You have two options to specify Connection String locally:

1. launchSettings.json (environmentVariables section)

  "environmentVariables": {
     "ASPNETCORE_ENVIRONMENT": "Development",
     "SQLAZURECONNSTR_SomeConnectionString": "DefaultEndpointsProtocol=blah"
   }

2. appSettings.json

  "ConnectionStrings": {
    "SomeConnectionString": "DefaultEndpointsProtocol=blah"
  }

Having either way will allow you to get the connection string setting by calling:

IConfiguration.GetConnectionString("SomeConnectionString")

Function call above will also work when deployed to Azure, as it is using EnvironmentVariables configuration provider to read settings.

Answer 2

The POSTGRESQLCONNSTR_ prefix isn't supported by the environment variables configuration provider. The docs shows this, in an indirect fashion, where it states that the following prefixes are supported:

• CUSTOMCONNSTR_
• MYSQLCONNSTR_
• SQLAZURECONNSTR_
• SQLCONNSTR_

It's also apparent in the source code for the provider.

There are a couple of options for working around this:

1. Change the Type to Custom in the Connection strings section of the Azure portal.
2. Change to an Application setting of ConectionStrings:db in the Azure portal.

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This is being tracked on GitHub: https://github.com/dotnet/runtime/issues/36123.