Configuration Providers in ASP.NET Core
💡 Concept Name
Configuration Providers
📘 Quick Intro
Configuration in ASP.NET Core is handled through a flexible system of providers—sources like JSON files, environment variables, command-line arguments, and even custom sources. These are layered in a specific order, allowing overriding behavior at runtime.
🧠 Analogy / Short Story
Imagine planning a trip with instructions from multiple people: a tour guide book (JSON), text messages from your friend (env vars), and last-minute tips from a driver (CLI args). The latest advice overrides the earlier ones. That’s how ASP.NET Core configuration works—layered and override-friendly.
🔧 Technical Explanation
ASP.NET Core uses an IConfigurationBuilder to set up its configuration pipeline. Providers are added in the desired order—
appsettings.jsonappsettings.{Environment}.json- Environment Variables
- Command-line Arguments
Each subsequent provider can override keys from earlier ones. This allows flexibility for local development, staging, and production environments.
🎯 Purpose & Use Case
- ✅ Load static configuration from
appsettings.json - ✅ Use env vars for sensitive secrets (e.g., API keys)
- ✅ Override settings at runtime via CLI for Docker/K8s
- ✅ Enable per-environment configuration
- ✅ Create custom providers (e.g., from database or Azure Key Vault)
💻 Real Code Example
var builder = WebApplication.CreateBuilder(args);
builder.Configuration
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json", optional: false)
.AddJsonFile($"appsettings.{builder.Environment.EnvironmentName}.json", optional: true)
.AddEnvironmentVariables()
.AddCommandLine(args);
var app = builder.Build();
Key Highlight: The order of providers decides override behavior. Command-line args override environment vars, which override JSON config.
❓ Interview Q&A
Q1: What are configuration providers in ASP.NET Core?
A: They are sources of app settings like JSON, env vars, CLI args, etc.
Q2: What’s the default order of configuration sources?
A: JSON → env vars → command-line.
Q3: How do you load secrets securely in ASP.NET Core?
A: Use environment variables or user-secrets in dev.
Q4: Can you override JSON values using env vars?
A: Yes, later sources override earlier ones.
Q5: What’s the purpose of AddCommandLine in config?
A: To override or provide values during runtime (e.g., docker).
Q6: Can you create a custom provider?
A: Yes, implement ConfigurationProvider.
Q7: Where does ASP.NET Core store env-specific config?
A: In appsettings.{env}.json files.
Q8: How do you bind configuration to POCO classes?
A: Using builder.Configuration.GetSection().Bind()
Q9: Are all config sources required?
A: No, they are optional and additive.
Q10: What’s IConfiguration in ASP.NET Core?
A: It is the abstraction used to access config data regardless of source.
📝 MCQs
Which file is commonly used to store configuration in ASP.NET Core?
Answer: appsettings.json
What overrides appsettings.json by default?
Answer: Environment variables
Which method adds environment variable provider?
Answer: AddEnvironmentVariables()
Which config provider runs last in the typical order?
Answer: Command-line arguments
What does AddCommandLine(args) do?
Answer: Adds CLI args as config values
Can you add multiple JSON config files?
Answer: Yes
What interface is used to access config values?
Answer: IConfiguration
What extension method binds config to classes?
Answer: Bind()
Where do you put app config for Docker?
Answer: Command-line or env vars
How to structure config per environment?
Answer: Use appsettings.{env}.json
💡 Bonus Insight
Using layered config makes your app portable and environment-friendly. Always follow the order: base config (JSON) → secrets (env) → overrides (CLI).
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