500.19 Error using Autofac MultiTenancy in Webforms - webforms

Question

I'm trying to modernize an existing multi-tenant WebForms with dependency injection using Autofac.
When I try to browse to a tenant directory, I get a 500.19 error.
HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid.
Config Error Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to 'ContainerDisposal'
Config Source:
60: <modules>
61: <add name="ContainerDisposal" type="Autofac.Integration.Web.ContainerDisposalModule, Autofac.Integration.Web" preCondition="managedHandler" />
62: <add name="PropertyInjection" type="Autofac.Integration.Web.Forms.PropertyInjectionModule, Autofac.Integration.Web" preCondition="managedHandler" />
These values are definitely not duplicated. I can browse to a page outside of the tenant directory without getting the error.
Here's how I'm creating the multitenant container.
var context = new TenantDbContext();
var tenantRepository = new TenantRepository(context);
var tenantService = new TenantService(tenantRepository);
var tenants = tenantService.List();
var builder = new ContainerBuilder();
var tenantIdStrategy = new TenantIdentificationStrategy();
builder.RegisterType<TenantDbContext>().InstancePerLifetimeScope();
builder.RegisterType<TenantRepository>().As<ITenantRepository>().SingleInstance();
builder.RegisterInstance(tenantIdStrategy).As<ITenantIdentificationStrategy>();
var multitenantContainer = new MultitenantContainer(tenantIdStrategy, builder.Build());
foreach (var tenant in tenants)
{
var connectionString = tenant.Provider;
multitenantContainer.ConfigureTenant(tenant.Name, b =>
{
b.Register(appContext => new AppDbContext(connectionString))
.InstancePerTenant()
.AsSelf();
b.RegisterType<CourseRepository>()
.As<ICourseRepository>();
});
}
_containerProvider = new ContainerProvider(multitenantContainer);
The example application can be found here: https://github.com/TonyaT3PO/WebForms.AutoFac.MultiTenant

Answer 1

I spent about 15 minutes trying to use your repro to see what's up but:
The instructions in the README to just run those EF commands doesn't work. The web app is where the connection strings are defined, but the data project is where the migrations are. Even if you get past that...
The connection strings refer to three different .mdf files that aren't checked in and don't get automatically created.
For future questions, I'd recommend coming up with a minimal repro. For example, the problem isn't with the database, so the repro doesn't need EF or databases or anything. The problem doesn't have to do with bundles or DTOs or repositories or any of that, so all that can go. There's a great article over here about creating a minimal reproducible example.
A minimal repro helps folks answer you. Like, if I can't get your repro running because it's too complex, I'm usually going to bail out and just not answer. If I can get it running - or, better, if the repro is small enough to fit right here in the question - then I'm far more likely to try helping out.
A minimal example can help you, too. I do this myself - remove moving pieces one by one until stuff starts working as expected, then add stuff back until it breaks again. You'll know which thing was added that started breaking and that's the bit you need to fix or ask about.
In the meantime:
I agree that you don't have ContainerDisposal defined twice. However, web.config has inheritance which is why you can define one at the root of your web app and one in a subfolder with overrides.
This is important to know because something that could be happening is that the server or machine level web.config may already have ContainerDisposal defined for you in which case it's not defined twice in the app-level web.config but once inheritance is applied, it is defined twice.
That inheritance thing isn't something we can debug from the repro - that's going to be something on the machine where you're running the app and seeing the problem.
If I could have run your repro, I could have verified whether or not I also see it; but since I can't, I'll have to leave you with "an exercise for the reader" to check that out. This blog article appears old, but it's still valid for web.config inheritance info. Hopefully it can help.

Answer 2

The 500.19 error was probably a red herring. My applicationHost.config file became corrupted. I got the same error running a known good project.
After Travis's feedback, I created a new, stripped-down project that mimics the minimal things I needed to accomplish.
Each tenant has its own directory.
The tenant pages load a user control.
The user control displays the tenant's data.
Pass the tenant's connection string to a class that needs it to get the data.
The new example can be found here https://github.com/TonyaT3PO/WebForms.Autofac.MultiTenant.Minimal