Configuration and the Options pattern — Modern .NET — Hosting, Configuration, DI & Deployment

4. Configuration and the Options pattern

Basic★ Must knowLesson 4 of 9

Sources, later overrides earlier: appsettings.json → appsettings.{ASPNETCORE_ENVIRONMENT}.json → User Secrets (Development) → environment variables → command-line args. Also Azure Key Vault and Azure App Configuration providers.

json

{
  "ConnectionStrings": { "Db": "Server=.;Database=Shop;Trusted_Connection=True;TrustServerCertificate=True" },
  "Smtp": { "Host": "smtp.example.com", "Port": 587 }
}

csharp

var host = builder.Configuration["Smtp:Host"];                   // ':' separates sections
// env var override: Smtp__Host=smtp.prod.example.com              ('__' in environment variables)
builder.Services.AddOptions<SmtpOptions>().BindConfiguration("Smtp").ValidateDataAnnotations().ValidateOnStart();

bash

dotnet user-secrets init
dotnet user-secrets set "Smtp:Password" "local-only-secret"