Why is the ILogger injected in my Azure Function v2 missing the APPINSIGHTS_INSTRUMENTATIONKEY?

I got confused with different variants of setup (ILogger vs ILoggerFactory vs other stuff).

In my Startup class, it is correct to call AddLogging (with a minimum level or not, as long as it is defined somewhere here or in the host.json file).

using InjectionHttpClientFactory;using Microsoft.Azure.WebJobs;using Microsoft.Azure.WebJobs.Hosting;using Microsoft.Extensions.DependencyInjection;using Microsoft.Extensions.Logging;[assembly: WebJobsStartup(typeof(Startup))]namespace InjectionHttpClientFactory{    public sealed class Startup : IWebJobsStartup    {        public void Configure(IWebJobsBuilder webJobsBuilder)        {            webJobsBuilder.Services.AddLogging();        }    }}

In the Azure Function, I have an error if I specify HttpClient as a parameter:

Microsoft.Extensions.DependencyInjection.Abstractions: Unable to resolve service for type 'Microsoft.Extensions.Logging.ILogger' while attempting to activate 'XXX'

However, it does work if I specify an ILoggerFactory. The instrumentation key property that was empty somehow has no impact.

I have updated the host.json file to include the logging information with the minimum severity level as well as configuration information for Application Insights:

{  "version": "2.0",  "logging": {    "fileLoggingMode": "debugOnly",    "logLevel": {      "default": "Trace"    },    "applicationInsights": {        "samplingSettings": {          "isEnabled": true,          "maxTelemetryItemsPerSecond" : 5        }    }  }}

Update

As mentioned in comments, Microsoft released an update which introduces the FunctionsStartup class which should be the preferred way of doing this.

[assembly: FunctionsStartup(typeof(MyNamespace.Startup))]namespace MyNamespace{    public class Startup : FunctionsStartup    {        public override void Configure(IFunctionsHostBuilder builder)        {            builder.Services.AddHttpClient();            builder.Services.AddSingleton((s) => {                return new CosmosClient(Environment.GetEnvironmentVariable("COSMOSDB_CONNECTIONSTRING"));            });            builder.Services.AddSingleton<ILoggerProvider, MyLoggerProvider>();        }    }}

    services.AddSingleton(context =>         {            var factory = context.GetRequiredService<ILoggerFactory>();            var loggingConfiguration = <get your app insights's instrumentation key from your configuration provider>;            var logger = new LoggerConfiguration()                    .WriteTo                    .ApplicationInsightsEvents(loggingConfiguration.ApplicationInsightsKey)                    .CreateLogger();            return factory.AddSerilog(logger).CreateLogger("MyLogger");        });

Logger needs to be configured prior to ingest telemetry with your app-insights. Design Usage(Serilog) pattern may be different as this is just a stub to explain.

Logger is passed as a function argument:

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