How to setup Serilog with Azure Functions v4 correctly?

For those that got here because they can't properly config their logging in an azure function with the app insights sink this is what works for me:

private static void ConfigureLogging(IServiceCollection services)
{
   Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Information()
        .MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
        .MinimumLevel.Override("System", LogEventLevel.Warning)
        .MinimumLevel.Override("Worker", LogEventLevel.Warning)
        .MinimumLevel.Override("Host", LogEventLevel.Warning)
        .MinimumLevel.Override("Function", LogEventLevel.Warning)
        .MinimumLevel.Override("Azure", LogEventLevel.Warning)
        .MinimumLevel.Override("DurableTask", LogEventLevel.Warning)
        .Enrich.FromLogContext()
        .Enrich.WithExceptionDetails()
        .WriteTo.ApplicationInsights(
            TelemetryConfiguration.CreateDefault(),
            TelemetryConverter.Events,
            LogEventLevel.Information)
        .CreateLogger();
        services.AddLogging(configure => configure.AddSerilog(Log.Logger));
}

The example here at the time of writing doesn't seem to work. The logging scope doesn't get captured in the output.

Serilog Version: 2.11.0

Serilog.Sinks.ApplicationInsights Version: 4.0.0

Linked example for the future:

[assembly: FunctionsStartup(typeof(MyFunctions.Startup))]
namespace MyFunctions
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.Services.AddSingleton<ILoggerProvider>((sp) => 
            {
                Log.Logger = new LoggerConfiguration()
                    .Enrich.FromLogContext()
                    .WriteTo.ApplicationInsights(sp.GetRequiredService<TelemetryClient>(), TelemetryConverter.Traces)
                    .CreateLogger();
                return new SerilogLoggerProvider(Log.Logger, true);
            });
        }
    }
}

For a Functions v4/ Isolated .NET 7 version of this

builder.ConfigureServices((hostingContext, services) =>
{ 
    Log.Logger = new LoggerConfiguration()
        .ReadFrom.Configuration(config)
        .Enrich.FromLogContext()
        .WriteTo.Console()
        .WriteTo.ApplicationInsights(TelemetryConfiguration.CreateDefault(), TelemetryConverter.Traces)
        .CreateLogger();

    services.AddLogging(lb => lb.AddSerilog(Log.Logger, true));
    services.AddApplicationInsightsTelemetryWorkerService();
    services.AddInterventionCalculatorServices(config);//injecting my services
});

Gets you serilog with sinks for console and Insights.

You can also configure the default logger within the hosts.json file

{
  "version": "2.0",
  "logging": {
    "logLevel": {
      "Function.MyFunctionName.User": "Information",
      "Function": "Error"
    }
}

To remove duplicate messages (there may be a way to turn off console entirely from here, but I've not found one).

After this, you should only be seeing your serilog sinks and only 1 set of the important console messages.

Note that recent versions of Visual studio have had some issues with copying files on "F5" (latest patch 17.7.0 Preview 3.0 to VS Community is supposed to resolve this, but I'm not sure its 100%). Make sure to rebuild after changing your hosts.json file and to verify whats in your deployed folder to retain your sanity...

To set up Serilog.ILogger instead of ILogger<T> you can add Serilog as Singleton

builder.AddSingleton<ILogger>(Log.Logger);

instead of

services.AddLogging(configure => configure.AddSerilog(Log.Logger));

and then in the function inject ILogger from Serilog instead of ILoggerFactory and log as

_logger.Information("awesome log");

I run isolated function in .net7

I'm answering it for Azure Functions v4 (Isolated mode).

Firstly, the Functions.csproj file structure is outlined below, allowing one to add the Serilog packages I am using.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <LangVersion>latest</LangVersion>
    <AzureFunctionsVersion>v4</AzureFunctionsVersion>
    <OutputType>Exe</OutputType>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
    <!-- Application Insights isn't enabled by default. See https://aka.ms/AAt8mw4. -->
    <!-- <PackageReference Include="Microsoft.ApplicationInsights.WorkerService" Version="2.22.0" /> -->
    <!-- <PackageReference Include="Microsoft.Azure.Functions.Worker.ApplicationInsights" Version="2.0.0" /> -->
    <PackageReference Include="Microsoft.Azure.Functions.Worker" Version="2.0.0" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore" Version="2.0.0" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.ServiceBus" Version="5.22.0" />
    <PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="2.0.0" />
    <PackageReference Include="Polly" Version="8.5.1" />
    <PackageReference Include="Refit.HttpClientFactory" Version="8.0.0" />
    <PackageReference Include="Serilog" Version="4.2.0" />
    <PackageReference Include="Serilog.Extensions.Logging" Version="9.0.0" />
    <PackageReference Include="Serilog.Settings.Configuration" Version="9.0.0" />
    <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0" />
    <PackageReference Include="Serilog.Sinks.Seq" Version="9.0.0" />
  </ItemGroup>
  <ItemGroup>
    <None Update="host.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="local.settings.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <CopyToPublishDirectory>Never</CopyToPublishDirectory>
    </None>
  </ItemGroup>
  <ItemGroup>
    <Using Include="System.Threading.ExecutionContext" Alias="ExecutionContext" />
  </ItemGroup>
</Project>

Second Program.cs as below

using ADS.Functions.Http;
using Microsoft.Azure.Functions.Worker.Builder;
using Microsoft.Extensions.Hosting;
using Serilog;

var builder = FunctionsApplication.CreateBuilder(args);
builder.Services.ConfigureServices(builder.Configuration);

try
{
    var app = builder.Build();
    Log.Information("Starting ADS.Functions...");
    app.Run();
}
catch (Exception ex)
{
    Log.Fatal(ex, "ADS.Functions startup failed.");
}
finally
{
    Log.CloseAndFlush();
}

And then service extensions are shown below.

using System.Text.Json;
using ADS.Functions.Services;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Refit;
using Serilog;

namespace ADS.Functions.Http;

public static class ServiceExtensions
{
    public static void ConfigureServices(this IServiceCollection services, IConfiguration configuration)
    {
        services.ConfigureLogging(configuration);        
    }

    private static void ConfigureLogging(this IServiceCollection services, IConfiguration configuration)
    {
        Log.Logger = new LoggerConfiguration()
            .ReadFrom.Configuration(configuration.GetSection("Serilog"))
            .Enrich.FromLogContext()
            .Enrich.WithProperty("ApplicationName", "ADS Functions")
            .WriteTo.Console()
            .CreateLogger();

        services.AddLogging(loggingBuilder =>
        {
            loggingBuilder.ClearProviders(); // Removes default Azure Functions logging
            loggingBuilder.AddSerilog();
        });
    }

    private static void ConfigureMtpApiHttpClient(this IServiceCollection services, IConfiguration configuration)
    {
        var apiBaseUrl = GetMtpApiBaseUrl(configuration);
        var refitSettings = CreateRefitSettings();

        services.AddRefitClient<IMtpApiAuthentication>(refitSettings)
            .ConfigureHttpClient(client => client.BaseAddress = apiBaseUrl);

        services.AddTransient<MtpAuthenticationHandler>();

        services.AddRefitClient<IMtpApi>(refitSettings)
            .ConfigureHttpClient(client => client.BaseAddress = apiBaseUrl)
            .AddHttpMessageHandler<MtpAuthenticationHandler>();
    }

    private static Uri GetMtpApiBaseUrl(IConfiguration configuration)
    {
        var baseUrl = configuration["MtpApi:BaseUrl"];
        if (string.IsNullOrWhiteSpace(baseUrl))
        {
            Log.Fatal("MTP API Base URL is missing in configuration.");
            throw new InvalidOperationException("MTP API Base URL is required.");
        }

        return new Uri(baseUrl);
    }

    private static RefitSettings CreateRefitSettings()
    {
        var jsonOptions = new JsonSerializerOptions
        {
            PropertyNamingPolicy = null // Ensures PascalCase serialization
        };

        return new RefitSettings
        {
            ContentSerializer = new SystemTextJsonContentSerializer(jsonOptions)
        };
    }
}

Finally the local.settings.json file as below

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"    
  },
  "Serilog": {
    "Using": ["Serilog.Sinks.Console", "Serilog.Sinks.Seq"],
    "LevelSwitches": {
      "$appLogLevel": "Information",
      "$seqSwitch": "Information",
      "$consoleSwitch": "Information"
    },
    "MinimumLevel": {
      "ControlledBy": "$appLogLevel",
      "Override": {
        "Default": "Warning",
        "Host": "Warning",
        "Function": "Warning",
        "System": "Warning",
        "Microsoft": "Warning",
        "Azure.Core": "Warning",
        "Worker": "Warning",
        "Microsoft.Hosting.Lifetime": "Information",
        "Microsoft.EntityFrameworkCore": "Warning",
        "Microsoft.AspNetCore.Authentication": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "Console",
        "Args": {
          "levelSwitch": "$consoleSwitch",
          "theme": "Serilog.Sinks.SystemConsole.Themes.SystemConsoleTheme::Literate, Serilog.Sinks.Console",
          "outputTemplate": "[{Timestamp:HH:mm:ss} {Level:u3}] {SourceContext} {Message:lj}{NewLine}{Exception}"
        }
      },
      {
        "Name": "Seq",
        "Args": {
          "levelSwitch": "$seqSwitch",
          "serverUrl": "http://localhost:5341",
          "outputTemplate": "{Timestamp:HH:mm:ss} [{Level:u3}] {SourceContext} {Message}{NewLine}{Exception} {Properties:j}",
          "shared": true
        }
      }
    ],
    "Enrich": ["FromLogContext", "WithMachineName"]
  }
}

If configured correctly, you will only see a single log from Serilog.