Configuration

ASP.NET Core configuration merges appsettings.json, environment-specific files, environment variables, and command-line args into one key-value system—accessed via IConfiguration or strongly typed options.

appsettings.json example

{
  "ConnectionStrings": {
    "Default": "Server=.;Database=AppDb;Trusted_Connection=true"
  },
  "Logging": { "LogLevel": { "Default": "Information" } }
}

Reading configuration

var conn = builder.Configuration.GetConnectionString("Default");
builder.Services.Configure<SmtpOptions>(
    builder.Configuration.GetSection("Smtp"));

Environment overrides

appsettings.Development.json overrides base settings when ASPNETCORE_ENVIRONMENT=Development. Production secrets belong in environment variables or Azure Key Vault—not committed JSON.

Important interview questions and answers

1. Q: Where store production secrets?
   A: Environment variables, secret managers, Key Vault—never plain text in git.
2. Q: IOptions vs IConfiguration?
   A: IOptions binds a section to a typed POCO with validation; IConfiguration is raw key lookup.

Self-check

1. Which file typically holds connection strings?
2. How does Development settings override Production defaults?