Configuration & appsettings.json in ASP.NET Core
💡 Concept Name
Configuration & appsettings.json in ASP.NET Core
📘 Quick Intro
ASP.NET Core uses a flexible configuration system that supports hierarchical key-value pairs from multiple sources like appsettings.json, environment variables, and command-line arguments.
🧠 Analogy / Short Story
Think of configuration like a personal assistant managing your preferences: one assistant reads your written notes (appsettings.json), another listens to your voice (environment variables), and another reads sticky notes you place (CLI). Whichever speaks last, wins.
🔧 Technical Explanation
ASP.NET Core builds configuration using the ConfigurationBuilder. It reads from sources in order and stores them as key-value pairs, which you can inject using the IConfiguration interface.
- appsettings.json: Default file for settings.
- appsettings.{Environment}.json: Overrides for specific environments.
- Environment Variables: Useful in Docker/Kubernetes.
- CLI Args: Highest priority if used.
🎯 Purpose & Use Case
- ✅ Store app configuration values
- ✅ Use different settings per environment
- ✅ Read connection strings and feature toggles
- ✅ Secure secrets via external providers
- ✅ Simplify config management in DevOps pipelines
💻 Real Code Example
Sample appsettings.json:
{
"Logging": {
"LogLevel": {
"Default": "Information",
"Microsoft": "Warning"
}
},
"ConnectionStrings": {
"DefaultConnection": "Server=.;Database=AppDb;Trusted_Connection=True;"
}
}
Reading values in C# (Program.cs or controller):
var config = builder.Configuration;
var connectionString = config.GetConnectionString("DefaultConnection");
var logLevel = config["Logging:LogLevel:Default"];
🎯 Interview Q&A
- Q: What is
IConfigurationin ASP.NET Core?
A: It provides a way to read config values from multiple sources like JSON, ENV, CLI, etc. - Q: How does ASP.NET Core load
appsettings.json?
A: It is added by default to the configuration pipeline inCreateDefaultBuilder. - Q: How to access strongly typed config in controllers?
A: Bind a POCO class and inject it usingIOptions<T>. - Q: What happens if multiple config sources have the same key?
A: Last source added overrides previous ones (later wins). - Q: Can you change config without restarting the app?
A: Yes, useIOptionsSnapshotfor scoped services. - Q: How to secure secrets instead of putting in appsettings?
A: Use environment variables orSecret Manager. - Q: Is
appsettings.Production.jsonautomatically used?
A: Yes, ifASPNETCORE_ENVIRONMENTis set to "Production". - Q: What is
ConfigureServicesmethod used for?
A: It registers services and configuration logic into DI. - Q: How to bind nested sections in config?
A: UseGetSection("Section")multiple times or bind whole object. - Q: What is the use of
AddJsonFilemethod?
A: It explicitly adds JSON config files to the configuration builder.
📝 MCQs
📝 MCQs
Q1. What interface is used to access configuration in ASP.NET Core?
- IConfig
- IOptions
- IConfiguration
- IAppSettings
Q2. What file format is used for default config in ASP.NET Core?
- XML
- YAML
- JSON
- INI
Q3. How to access settings in a strongly typed way?
- IValue
- IAppConfig
- IOptions
- IBind
Q4. What happens if ENV and appsettings.json have the same key?
- JSON wins
- ENV value wins
- Both fail
- It throws error
Q5. Which method loads appsettings.json by default?
- ConfigureBuilder
- AddConfig
- CreateDefaultBuilder
- UseDefaults
Q6. Which config source is used for command line arguments?
- EnvConfig
- CommandLine
- RuntimeArgs
- ConsoleReader
Q7. How can secrets be securely stored?
- appsettings.json
- public.json
- Environment.cs
- Secret Manager
Q8. Which method binds config section to POCO?
- UseConfig()
- GetValue()
- GetSection().Bind()
- MapConfig()
Q9. What is the use of IOptionsSnapshot?
- Singleton access
- Scoped config updates
- Logging
- Debugging
Q10. How to use different config for prod & dev?
- Multiple apps
- Rewrite settings
- Environment-specific JSON files
- Change app.cs
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