Example of multitenant with generic host in C#

Question

I have not found a solution (or example of) using multitenancy with a generic host in C#.

The examples given in the Autofac repository (ConsoleApp, MVC and WCF) uses a strategy that is not supported (as I see it) with generic host (Autofac needs access to an IContainer instance to create multitenancy container(s)).

Is there a way to use multitenancy with generic host and Autofac?

Thanks!

I've read the examples in the Autofac github repository and experimented a bit, but did not find a solution.

Here are the links to the examples

• Generic host
• Console app
• MVC app
• WCF app

To be more concrete, this is a standard generic host example that is from the code when experimenting, and I've put comments to highlight the issue at hand

using Autofac;
using Autofac.Extensions.DependencyInjection;
using Autofac.Multitenant;

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace AutoFacMultiTenantExploration;

internal class Program
{
    static async Task Main(string[] args)
    {
        AutofacServiceProviderFactory factory = new();

        var host = Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(factory)
            .ConfigureServices(ConfigureServices)
            .ConfigureContainer<ContainerBuilder>(ConfigureContainer)
            .UseConsoleLifetime()
            .Build();

        //var mtc = new MultitenantContainer(_myTenantIdentificationStrategy, IContainer instance needed here...);

        await host.RunAsync();
    }

    private static void ConfigureServices(HostBuilderContext context, IServiceCollection collection)
    {
        //var mtc = new MultitenantContainer(_myTenantIdentificationStrategy, IContainer instance needed here...);

        collection.AddHostedService<HostedService>();
        collection.AddSingleton<MyTenantIdentificationStrategy>();
    }

    private static void ConfigureContainer(HostBuilderContext context, ContainerBuilder builder)
    {
        //var mtc = new MultitenantContainer(_myTenantIdentificationStrategy, IContainer instance needed here...);

        builder.RegisterType<Logger>().As<ILogger>();
    }
}

// IContainer is not registered by the generic host, so it's not possible to inject an instance here with the service IHostedService
internal class HostedService(ILogger logger) : IHostedService
{
    private readonly ILogger _logger = logger;

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Starting hosted service");

        //var mtc = new MultitenantContainer(_myTenantIdentificationStrategy, IContainer instance needed here...);


        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Stopping hosted service");
        return Task.CompletedTask;
    }
}
internal class Logger : ILogger
{
    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
    {
        Console.Out.WriteLineAsync($"Logger: {formatter.Invoke(state, exception)}");
    }

    public bool IsEnabled(LogLevel logLevel)
    {
        throw new NotImplementedException();
    }

    public IDisposable? BeginScope<TState>(TState state) where TState : notnull
    {
        throw new NotImplementedException();
    }
}

internal class MyTenantIdentificationStrategy : ITenantIdentificationStrategy
{
    public int Identity { get; set; } = 0;

    public bool TryIdentifyTenant(out object? tenantId)
    {
        tenantId = Identity;
        return true;
    }
}

Answer 1

The docs for ASP.NET Core integration show how this can work, but you might need to mold it a little to your needs. The Autofac.AspNetCore.Multitenant package is the key.

For example, you could do something like this:

public static class Program
{
    public static async Task Main(string[] args)
    {
        await Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(
               new AutofacMultitenantServiceProviderFactory(ConfigureMultitenantContainer))
            .ConfigureServices(ConfigureServices)
            .ConfigureContainer<ContainerBuilder>(ConfigureContainer)
            .RunConsoleAsync();
    }


    private static void ConfigureServices(IServiceCollection services)
    {
        // Register things with MS DI.
    }

    private static void ConfigureContainer(ContainerBuilder containerBuilder)
    {
        // Register things that are shared across all tenants.
    }

    private static MultitenantContainer ConfigureMultitenantContainer(IContainer container)
    {
        var strategy = new YourTenantIdStrategy();
        var multitenantContainer = new MultitenantContainer(strategy, container);
        // Register things for various tenants.
        return multitenantContainer;
    }
}