Using Application settings of Azure App Service resulting into an HTTP 500 error

Question

I am using Shared tier to deploy my .NET Core web app to Azure.

Below is my app.config file,

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <appSettings>
    <add key="SASToken" value="" />
    <add key="StorageAccountPrimaryUri" value="" />
    <add key="StorageAccountSecondaryUri" value="" />
  </appSettings>
</configuration>

Under Application settings on Azure Portal, I have updated the following things,

But, when I access my API, I get Http 500 error with the below exception details,

System.ArgumentException: The argument must not be empty string. Parameter name: sasToken at Microsoft.WindowsAzure.Storage.Core.Util.CommonUtility.AssertNotNullOrEmpty(String paramName, String value) at Microsoft.WindowsAzure.Storage.Auth.StorageCredentials..ctor(String sasToken) at ProfileVariable.DataAccessor.AzureTableStorageAccount.TableStorageAccount.ConfigureAzureStorageAccount() in C:\Users\sranade\Source\Repos\ProfileVariableService\ProfileVariable.DataAccessor\AzureTableStorageAccount\TableStorageAccount.cs:line 22

Answer 1

For .NET Core web app, we usually put settings in appsettings.json.

{
  "SASToken": "TOKENHERE",
  "StorageAccountPrimaryUri":"CONNECTIONSTRING",
  ...
}

To get value in appsetting.json, leverage IConfiguration object injected.

1. Refactor your code with Interface and add IConfiguration field.

   public interface ITableStorageAccount { string Method(); }
   
   public class TableStorageAccount : ITableStorageAccount
   {
   
       private readonly IConfiguration Configuration;
   
       public TableStorageAccount(IConfiguration configuration)
       {
           Configuration = configuration;
       }
   
       // an example return table storage uri
       public string Method()
       {
           string cre = Configuration["SASToken"];
           CloudTableClient table = new CloudTableClient(new Uri("xxx"), new StorageCredentials(cre));
           return table.BaseUri.AbsolutePath;
       }
   }
   

2. Config dependency injection in startup.cs

   public void ConfigureServices(IServiceCollection services)
   {
       ...
       services.AddSingleton<ITableStorageAccount, TableStorageAccount>();
   }
   

3. Use the service in controller.

   private readonly ITableStorageAccount TableStorageAccount;
   
   public MyController(ITableStorageAccount TableStorageAccount)
   {
       this.TableStorageAccount = TableStorageAccount;
   }
   

In Program.cs template.

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .Build();

CreateDefaultBuilder() does the work of loading configurations like appsetting.json, see more details in docs.