Use logging in ConfigureAppConfiguration method in ASP.NET Core

Question

I have certian code in ConfigureAppConfiguration method I want to add few logs here I tried writing below code but it fails how can I fix this? Or is there any other way to do logging in this method:

public static IWebHostBuilder AddKeyVault(this IWebHostBuilder builder)
{
    return builder.ConfigureAppConfiguration(
        (context, config) =>
        {
            var loggerFactory = builder.Build().Services.GetRequiredService<ILoggerFactory>(); // code fails here
            var logger = loggerFactory.CreateLogger(typeof(WebHostBuilderCustomExtension));
            //  if (context.HostingEnvironment.IsProduction())
            {
                var cert = new X509Certificate2(File.ReadAllBytes("keyvaultcertificate.pfx"));
            
                var builtConfig = config.Build();
                
                config.AddAzureKeyVault(builtConfig["vaultname"], "8c372a04-8578-4c38-a58d-a821d85212cb",cert);
                logger.LogInformation($"connected to key vault {builtConfig["azure.keyvault.uri"]}");
            }

        });
}

I get the error below when I run this code:

This is how this method is called:

return WebHost.CreateDefaultBuilder(args).AddKeyVault()
    .UseStartup<Startup>();

If you say something like "it fails" or "there's an error", that should immediately and always be followed with a description of the problem and/or exception and stack trace. — Chris Pratt
– Chris Pratt, Commented Aug 2, 2019 at 13:41
How did you call return builder.ConfigureAppConfiguration? Share us your current program.cs. What is the relationship between your first part and last part code? — Edward
– Edward, Commented Aug 5, 2019 at 7:13
@TaoZhou program.cs contains only last part of code , i updated first part of code it is under extension method AddKeyVault() which i created — ankush
– ankush, Commented Aug 5, 2019 at 8:58

Edward · Accepted Answer · 2019-08-05 09:43:20Z

3

For IWebHostBuilder, you could not build it twice as the error indicates.

For ServiceCollection, you will not be able to access the services like ILoggerFactory before build the host.

For a workaround, you will need to initialize your own ILoggerFactory manually like.

public static class WebHostBuilderCustomExtension
{
    public static IWebHostBuilder AddKeyVault(this IWebHostBuilder builder)
    {
        return builder.ConfigureAppConfiguration(
                        (context, config) =>
                        {
                            var loggerFactory = new LoggerFactory(); 
                            loggerFactory.AddConsole();
                            var logger = loggerFactory.CreateLogger(typeof(WebHostBuilderCustomExtension));
                            logger.LogInformation($"connected to key vault ");
                        });
    }
}

answered Aug 5, 2019 at 9:43

Edward

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2 Comments

ankush Over a year ago

loggerFactory.AddConsole(); gives an obsolete warning how to handle that?

Edward Over a year ago

@ankush loggerFactory.AddConsole(); is a demo code which is used to add ConsoleLoggerProvider, add your own logerProvider.

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