Question:

When to use Configure() to set up dependency injection?

Problem:

I understand the differences between AddTransient(), AddScoped() and AddSingleton() when configuring services. But I'm having trouble finding good information about Configure().

It seems I can use them all interchangeably. The only real difference I see is that when you use Configure(), you have to deal with that somewhat annoying IOptions component.

Are there hard and fast rules about when I should use Configure() instead any of the Add... methods? Can someone link to a good article on this. (Every time I Google it, I just get a discussion on the differences between AddTransient(), AddScoped() and AddSingleton().)

Solution:

OP's question is actually on service.Configure<> vs AddTransient(), AddScoped() and AddSingleton().

I will just supplement on this >answer.

>service.Configure

Registers a configuration instance that TOptions will bind against, and updates the options when the configuration changes.

It's used to bind a section of the configuration to a strongly typed object. It allows you to define options by binding configuration sections to instances of classes representing those options.

From >source, You will see this method under the hood eventually does the following:

Add IOptionsSnapshot<> service with lifetime Scoped.
Add IOptionsMonitor<> service with lifetime Singleton.
Add IOptionsFactory<> service with lifetime transient.
Add IOptionsMonitorCache<> with Singleton lifetime.
Add IOptions<> with Singleton Lifetime to DI Container.

As far as using AddTransient or AddScoped to add IOptions<TOptions> is inadvisable, if you want to read configuration changes take a look at >IOptionsMonitor,>IOptionsSnapshot