How can I use the new DI to inject an ILogger into an Azure Function using IWebJobsStartup?

Question

I am using Azure Function v2. Here is my function that uses the constructor injection:

public sealed class FindAccountFunction
{
    private readonly IAccountWorkflow m_accountWorkflow;

    private readonly IMapper m_mapper;

    private readonly ILogger m_logger;

    public FindAccountFunction(ILogger logger, IMapper mapper, IAccountWorkflow accountWorkflow)
    {
        m_logger = logger;
        m_mapper = mapper;
        m_accountWorkflow = accountWorkflow;
    }

    [FunctionName("FindAccount")]
    public async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Function, Verbs.Get, Route = "v1/accounts/")] HttpRequest httpRequest, ILogger logger)
    {
        // Do stuff.
    }
}

I am declaring all the dependencies that I want to inject into my Azure Function in the Startup class that derives from IWebJobsStartup:

    public sealed class Startup : IWebJobsStartup
    {
        public void Configure(IWebJobsBuilder webJobsBuilder)
        {
            //  Registers the application settings' class.
            webJobsBuilder.Services.AddSingleton<IApplicationSettings, ApplicationSettings>();

            //  ** Registers the ILogger instance **
            //  ** ?? **

            //  Registers the IMapper instance for the contracts.
            var mapperConfiguration = new MapperConfiguration(cfg => cfg.AddProfile(new MyProfile()));

     webJobsBuilder.Services.AddSingleton(mapperConfiguration.CreateMapper());

            // Registers custom services.
            webJobsBuilder.Services.AddTransient<IStorageService, StorageService>();

            webJobsBuilder.Services.AddTransient<IAccountWorkflow, AccountWorkflow>();
        }
   }

The Azure Function calls other injected services that do depends on the ILogger as well, such as the IAccountWorkflow:

public sealed class AccountWorkflow : IAccountWorkflow
{  
    public AccountWorkflow(ILogger logger, IStorageService storageService)
    {
        if(logger is null)
            throw new ArgumentNullException();
    }
}

The problem is that the DI is unable to find any ILogger implementation and fails to resolve services since a null ILogger is injected.

Question

How can I setup the injection of the ILogger in IWebJobsStartup?

Answer 1

UPDATE

Reference Use dependency injection in .NET Azure Functions

Registering services

To register services, you can create a configure method and add components to an IFunctionsHostBuilder instance. The Azure Functions host creates an IFunctionsHostBuilder and passes it directly into your configured method.

To register your configure method, you must add an assembly attribute that specifies the type for your configure method using the FunctionsStartup attribute.

So in this case

[assembly: FunctionsStartup(typeof(MyNamespace.Startup))]    
namespace MyNamespace {
    public class Startup : FunctionsStartup {
        public override void Configure(IFunctionsHostBuilder builder) {
            //  ** Registers the ILogger instance **
            builder.Services.AddLogging();

            //  Registers the application settings' class.
            //...

            //...omitted for brevity    
        }
    }
}

ORIGINAL

I believe since you have access to the service collection, you should be able to add logging to it

public void Configure(IWebJobsBuilder webJobsBuilder) {       

    //  ** Registers the ILogger instance **
    webJobsBuilder.Services.AddLogging();

    //OR
    //webJobsBuilder.Services.AddLogging(builder => {
    //    //...
    //});

    //  Registers the application settings' class.
    //...

    //...removed for brevity
}

and having anILoggerFactory in the Function's constructor.

//...

//Ctor
public FindAccountFunction(ILoggerFactory loggerFactory, IMapper mapper, IAccountWorkflow accountWorkflow) {
    m_logger = loggerFactory.CreateLogger<FindAccountFunction>();
    m_mapper = mapper;
    m_accountWorkflow = accountWorkflow;
}

//...

Answer 2

I managed to resolve this problem:

Injecting into my class as below:

MyClass.cs:

public class MyClass
{
    private readonly ILogger<MyClass> _logger;

    public MyClass(ILogger<MyClass> logger)
    {
        _logger = logger;
    }
}

Startup.cs:

[assembly: FunctionsStartup(typeof(Namespace.Startup))]   

namespace Namespace {    
public class Startup : FunctionsStartup 
{
    public override void Configure(IFunctionsHostBuilder builder) 
    {
        builder.Services.AddLogging(); 
    }
  }
}

Answer 3

You should remove the call of AddLogging method from your startup class. The default logger is already setup by the azure function host.

[assembly: WebJobsStartup(typeof(StartUp))]
public class StartUp : IWebJobsStartup
{
    public void Configure(IWebJobsBuilder builder)
    {
        builder.Services.AddSingleton<AppSettings>();

        builder.Services.AddTransient<IMyService, MyService>();
    }
}

public MyFunction(IMyService service, ILogger<IMyService> logger)
{
    this.service = service;
    this.logger = logger;
}

Instance methods are now supported with azure function since Azure Functions Runtime 2.0.12265

Answer 4

In addition to registering the class in function Startup class, we would need to add the namespace in host.json file as well in order to log the messages to App insights. If we don't add it, it will simply log the message to console locally but when deployed on azure, it won't log anything and won't give any error either.

{
  "version": "2.0",
  "logging": {
    "logLevel": {
      "FunctionProjectNameSpace.RegisteredClass": "Information"
    }
  }
}

Sample code here for reference - https://gist.github.com/nareshnagpal06/82c6b4df2a987087425c32adb58312c2

Answer 5

You can add

  "logging": {
    "fileLoggingMode": "debugOnly",
    "logLevel": {
      "default": "Information"
    }
  }

without the need to add DI if you want to use IloggerFactory