.net core kestrel service can’t use configuration

I have set up a .net core application on linux using nginx. It works perfectly with dotnet MyProject.dll. However, using the instructions in this link, when I try setting up a kestrel service, it doesn’t seem to be able to use the Configuration in the startup class. Here is my Program

public class Program
{

    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args)
    {

        var configEnv = new ConfigurationBuilder().AddEnvironmentVariables().Build();

        return WebHost.CreateDefaultBuilder(args)
            .UseKestrel()
            .ConfigureAppConfiguration((ctx, builder) =>
            {
                var keyVaultEndpoint = configEnv["KEYVAULT_ENDPOINT"];
                if (!string.IsNullOrEmpty(keyVaultEndpoint))
                {
                    var azureServiceTokenProvider = new AzureServiceTokenProvider();
                    var keyVaultClient = new KeyVaultClient(
                        new KeyVaultClient.AuthenticationCallback(
                            azureServiceTokenProvider.KeyVaultTokenCallback));
                    builder.AddAzureKeyVault(
                    keyVaultEndpoint, keyVaultClient, new DefaultKeyVaultSecretManager());
                }
            })
            .UseStartup<Startup>()
            .UseUrls("http://localhost:5050")
            .Build();
    }
}

My start up class has the following:

services.AddDbContext<ApplicationDBContext>(config => {
    config.UseMySql(Configuration["ConnectionString"]);
});

I keep getting an error saying that the connectionString parameter attribute can’t be null when I run it with kestrel. The connection string is set up in azure key vault. This and all other secrets work when I do dotnet MyProject.dll. When using the kestrel service, I have also tried setting the environment variable, it still doesn’t shows the same error.

This is my kestrel service:

[Unit]
Description=Example.NET Web API App running on Ubuntu

[Service]
WorkingDirectory =/ home / MyProject / publish2 / files
ExecStart=/usr/bin/dotnet /home/MyProject/publish2/files/MyProject.dll
Restart = always
RestartSec=10  # Restart service after 10 seconds if dotnet service crashes
SyslogIdentifier=dotnet-example
User = www - data
#Environment=ASPNETCORE_ENVIRONMENT=Production
#Environment=DOTNET_PRINT_TELEMETRY_MESSAGE=false/etc/systemd/system/

[Install]
WantedBy=multi-user.target

I had tried with and without commenting the environment variables above. same result. Is there something I have to add for my kestrel service?

Update Even tried setting Environment=ConnectionString in the service file, still the same.

Answer

It turns out the only environment variables the .net core reads when ran using a service are the variables configured within the service file. Adding it in this file resolved the issue:

Environment=KEYVAULT_ENDPOINT=myendpointurlhere

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Answer