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The Currency Exchange API uses appsettings.json for configuration management, following .NET’s standard configuration patterns.

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Configuration Files

The application supports multiple configuration files for different environments:
  • appsettings.json - Base configuration for all environments
  • appsettings.Development.json - Development-specific overrides
  • appsettings.Production.json - Production-specific overrides (create as needed)

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appsettings.json Structure

Here’s the complete structure of the main configuration file: 
{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },

  "Kestrel": {
    "Endpoints": {
      "MyHttpEndpoint": {
        "Url": "http://*:8080"
      }
    }
  },
  
  "ConnectionStrings": {
    "CurrencyExchangeDBContext": "Host=postgres;Database=currencies;Port=5432;User ID=alexpg;Password=76t34qVBh3;CommandTimeout=1200;"
  },
  
  "CorsConfig": {
    "Origin": [
      "http://localhost:4200"
    ]
  },
  
  "ExternalUrls": {
    "CBRUrl": "https://www.cbr-xml-daily.ru/daily_utf8.xml"
  },
  
  "CurrencyReceiptPeriod": {
    "Period": "300"
  },
  
  "AllowedHosts": "*"
}

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Configuration Sections

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Logging

Controls the logging behavior of the application: 
"Logging": {
  "LogLevel": {
    "Default": "Information",
    "Microsoft.AspNetCore": "Warning"
  }
}
SettingDefaultDescription
DefaultInformationDefault log level for all categories
Microsoft.AspNetCoreWarningLog level for ASP.NET Core framework logs
Available Log Levels: Trace, Debug, Information, Warning, Error, Critical, None

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Kestrel Web Server

Configures the HTTP endpoints for the Kestrel web server: 
"Kestrel": {
  "Endpoints": {
    "MyHttpEndpoint": {
      "Url": "http://*:8080"
    }
  }
}
The API listens on port 8080 by default. The * wildcard means it accepts connections on all network interfaces.

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Connection Strings

Defines database connection parameters: 
"ConnectionStrings": {
  "CurrencyExchangeDBContext": "Host=postgres;Database=currencies;Port=5432;User ID=alexpg;Password=76t34qVBh3;CommandTimeout=1200;"
}
Connection String Parameters:
ParameterValueDescription
HostpostgresDatabase server hostname (Docker service name)
DatabasecurrenciesDatabase name
Port5432PostgreSQL port
User IDalexpgDatabase user
Password76t34qVBh3Database password
CommandTimeout1200Command timeout in seconds (20 minutes)
Never commit passwords directly in configuration files for production. Use environment variables or secure secret management instead.

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CORS Configuration

Configures Cross-Origin Resource Sharing (CORS) policies: 
"CorsConfig": {
  "Origin": [
    "http://localhost:4200"
  ]
}
The CORS configuration is implemented in Program.cs (lines 52-58): 
app.UseCors(policy =>
    {
        policy.WithHeaders().AllowAnyHeader();
        policy.WithOrigins(corsConfig);
        policy.WithMethods().AllowAnyMethod();
    }
);
Features:
  • Allows any HTTP headers
  • Allows any HTTP methods (GET, POST, PUT, DELETE, etc.)
  • Restricts origins to those listed in the configuration
Add your frontend URL to the Origin array to allow cross-origin requests from your client application.

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External URLs

Configures external API endpoints: 
"ExternalUrls": {
  "CBRUrl": "https://www.cbr-xml-daily.ru/daily_utf8.xml"
}
ParameterDescription
CBRUrlCentral Bank of Russia (CBR) daily exchange rates XML feed
The application uses this URL to fetch current exchange rates from the Russian Central Bank.

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Currency Receipt Period

Controls how frequently the application fetches exchange rates: 
"CurrencyReceiptPeriod": {
  "Period": "300"
}
ParameterDefaultDescription
Period300Time in seconds between exchange rate updates (5 minutes)
This is configured in Program.cs (lines 29-33): 
builder.Services.AddHostedService(provider =>
{
    var scopeFactory = provider.GetRequiredService<IServiceScopeFactory>();
    return new CBRExchangeRate(scopeFactory, currencyReceiptPeriod);
});

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Allowed Hosts

"AllowedHosts": "*"
Specifies which host headers are allowed. The wildcard * allows all hosts.
For production deployments, specify exact hostnames instead of using the wildcard:
"AllowedHosts": "api.yourdomain.com;yourdomain.com"

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Environment Variables

You can override any configuration setting using environment variables with the following pattern: 
# Format: Section__SubSection__Property
export ConnectionStrings__CurrencyExchangeDBContext="Host=localhost;Database=currencies;Port=5432;User ID=admin;Password=secret;"
export CorsConfig__Origin__0="http://localhost:3000"
export ExternalUrls__CBRUrl="https://alternative-url.com/rates.xml"
export CurrencyReceiptPeriod__Period="600"
1

Create an environment file

Create a .env file in your deployment directory:
# Database Configuration
DB_HOST=postgres
DB_NAME=currencies
DB_PORT=5432
DB_USER=alexpg
DB_PASSWORD=your_secure_password

# CORS Origins (comma-separated)
CORS_ORIGINS=http://localhost:4200,https://yourdomain.com

# External APIs
CBR_URL=https://www.cbr-xml-daily.ru/daily_utf8.xml

# Update frequency (seconds)
RATE_UPDATE_PERIOD=300
2

Load environment variables in Docker

Update your docker-compose.yaml or Docker run command to use the environment file:
services:
  app:
    image: currencyexchangeback
    env_file:
      - .env
    environment:
      ConnectionStrings__CurrencyExchangeDBContext: "Host=${DB_HOST};Database=${DB_NAME};Port=${DB_PORT};User ID=${DB_USER};Password=${DB_PASSWORD};CommandTimeout=1200;"
      CorsConfig__Origin__0: "${CORS_ORIGINS}"
      ExternalUrls__CBRUrl: "${CBR_URL}"
      CurrencyReceiptPeriod__Period: "${RATE_UPDATE_PERIOD}"

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Production Configuration

For production deployments, create an appsettings.Production.json file: 
{
  "Logging": {
    "LogLevel": {
      "Default": "Warning",
      "Microsoft.AspNetCore": "Error"
    }
  },
  
  "ConnectionStrings": {
    "CurrencyExchangeDBContext": "Host=${DB_HOST};Database=${DB_NAME};Port=${DB_PORT};User ID=${DB_USER};Password=${DB_PASSWORD};CommandTimeout=1200;"
  },
  
  "CorsConfig": {
    "Origin": [
      "https://yourdomain.com",
      "https://www.yourdomain.com"
    ]
  },
  
  "AllowedHosts": "api.yourdomain.com;yourdomain.com"
}
The application automatically loads the correct configuration file based on the ASPNETCORE_ENVIRONMENT environment variable.

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Configuration Best Practices

Use Environment Variables

Store sensitive information like passwords and API keys in environment variables, not in configuration files.

Separate by Environment

Maintain separate configuration files for development, staging, and production environments.

Secure CORS Settings

Only allow specific trusted origins in production. Never use wildcards.

Monitor Logs

Use appropriate log levels for each environment. More verbose in development, less in production.

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Validation

The application validates critical configuration settings at startup (see Program.cs:12-13): 
var corsConfig = builder.Configuration.GetSection("CorsConfig:Origin").Get<string[]>()
                 ?? throw new ArgumentNullException(@"CorsConfig:Origin is required.");
If required configuration is missing, the application will fail to start with a clear error message.

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Configuration Reference

For more information about .NET configuration, see:

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