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How does the command-line configuration provider let you override settings via arguments when running an application? How does the order of configuration provider registration affect which value wins when the same key is defined in multiple sources? What is the difference between IOptions<T>, IOptionsSnapshot<T>, and IOptionsMonitor<T>? How does the configuration binder handle nested objects, arrays, and complex types when binding a JSON section to a C# class? How does configuration hot-reload work with reloadOnChange for appsettings.json, and what are its limitations? How would you write a custom configuration provider to load settings from an unsupported source, like a remote database? How would you design configuration for a multi-tenant application where each tenant needs different settings resolved at runtime?
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.NET › Configuration & Options

How does named options support configuring multiple distinct instances of the same options type?

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Answer

Named options let you register multiple configurations of the same C# options class under different string names (via Configure<T>(name, ...)), then resolve a specific named instance using IOptionsSnapshot<T>.Get(name) or IOptionsMonitor<T>.Get(name) -- useful when you need several independently-configured instances of the same settings shape, like multiple SMTP configurations for different notification types.
builder.Services.Configure<SmtpSettings>("Marketing", builder.Configuration.GetSection("Smtp:Marketing"));
builder.Services.Configure<SmtpSettings>("Transactional", builder.Configuration.GetSection("Smtp:Transactional"));

public class EmailService {
    public EmailService(IOptionsSnapshot<SmtpSettings> options) {
        var marketingSettings = options.Get("Marketing");
        var transactionalSettings = options.Get("Transactional");
    }
}
Real-world example An application sending both marketing newsletters (via a bulk email provider) and transactional receipts (via a different, more reliable SMTP relay) uses named options to maintain two independently-configured SmtpSettings instances from the same class definition.

Common follow-ups: How does the default (unnamed) options instance relate to named ones?;Can you validate each named instance independently?

Configuration & Options;Dependency Injection
All 15 Configuration & Options questions