Integrating Autofac With Dotnet

Register Autofac with ASP.NET Core

Overview

When migrating from ASP.NET Framework to ASP.NET Core, Autofac integration changes significantly. The old pattern of manually building a container and setting DependencyResolver is replaced by registering Autofac as the host's service provider factory. This ensures Autofac participates in the standard DI lifecycle rather than bypassing it.

> Related skill: If the goal is to remove Autofac entirely and replace with built-in DI, use migrating-autofac-to-dotnet-di instead.

Workflow

Migration Progress:
- [ ] Step 1: Verify Autofac usage
- [ ] Step 2: Install required package
- [ ] Step 3: Locate and extract existing registrations
- [ ] Step 4: Register Autofac as service provider factory
- [ ] Step 5: Migrate container registrations
- [ ] Step 6: Remove obsolete integration code
- [ ] Step 7: Validate

Step 1: Verify Autofac usage

• Confirm the project uses Autofac for dependency injection. If not, skip — inform the user there is nothing to do.
• Check if Program.cs already calls UseServiceProviderFactory(new AutofacServiceProviderFactory()). If so, verify the container configuration is correct and skip remaining steps.

Step 2: Install required package

Install Autofac.Extensions.DependencyInjection with a version matching the project's target framework. This package provides the AutofacServiceProviderFactory bridge between Autofac and the .NET hosting model.

Step 3: Locate and extract existing registrations

Search for Autofac registration code that builds a container — typically in Global.asax.cs, Startup.cs, or other top-level initialization classes. Record all ContainerBuilder registrations and module registrations before removing that code.

> Why remove first? The old code manually calls builder.Build() and sets a DependencyResolver, which conflicts with the host-managed container lifecycle in ASP.NET Core.

Step 4: Register Autofac as service provider factory

Add to Program.cs:

builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());

Step 5: Migrate container registrations

Move all extracted registrations into a ConfigureContainer block in Program.cs:

builder.Host.ConfigureContainer<ContainerBuilder>(containerBuilder =>
{
    containerBuilder.RegisterType<MyService>().As<IMyService>();
    containerBuilder.RegisterModule(new MyAutofacModule());
});

Omit any calls to builder.Build() or resolver setup — the host handles container building automatically.

Step 6: Remove obsolete integration code

Delete ASP.NET Framework-specific Autofac wiring such as:

• DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
• GlobalConfiguration.Configuration.DependencyResolver = resolver;
• Manual ContainerBuilder.Build() calls in startup code

Step 7: Validate

• Build the project and fix any compilation errors.
• Verify services resolve correctly at runtime.

Example

Before (Global.asax.cs or Startup.cs):

var builder = new ContainerBuilder();
builder.RegisterType<MyService>().As<IMyService>();
builder.RegisterType<MyRepository>().As<IRepository>();
builder.RegisterModule<MyModule>();
var container = builder.Build();
DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

After (Program.cs):

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());

builder.Host.ConfigureContainer<ContainerBuilder>(containerBuilder =>
{
    containerBuilder.RegisterType<MyService>().As<IMyService>();
    containerBuilder.RegisterType<MyRepository>().As<IRepository>();
    containerBuilder.RegisterModule<MyModule>();
});

var app = builder.Build();

Success Criteria

• Autofac.Extensions.DependencyInjection package installed
• UseServiceProviderFactory configured in Program.cs
• All registrations and modules migrated to ConfigureContainer block
• Obsolete DependencyResolver and manual Build() calls removed
• Project compiles and services resolve correctly at runtime