Web.Config and Machine.Config

• Manage settings at application level.
• XML Format
• Visual Studio create we.config for each project (by default).
• Application can execute without web.config, but debug cannot.
• Changes in web.config, no need reboot the web server.
• Sub Folder web conig can be overwrrite main web config.
• Able to reference another config <appSettings configSource="appSettings.config" />

1. Config Sections
• Handle configuration section.
2. Application Settings
• Storing application-wide name-value pairs for read only access.
3. Connection Strings
4. System.Web
• Authentication
• Authorization
• Caching
• CustomErrors
• Deployment
• HostingEnvironment
• Identity
• Membership
• Pages
• URL Mappings
• Web Controls
• Web Services
• ......

Machine.Config

• Master configuration file on your system with a lot of default settings. 
• The settings of Machine.config file are applied to the whole asp.net applications on your server.
• Web.config is the file for the local settings to be applied for a website or application.
• Each .NET Framework version has only one machine.config file , at the same time, each web application has its own web.config file.
• The machine.config file is at the highest level in the configuration hierarchy while Web.config file is to override the settings from the machine.config file.
• Get the Machine Config Path Response.Write(ConfigurationManager.OpenMachineConfiguration().FilePath);
• C:\Windows\Microsoft.NET\Framework\v2.0.50727\CONFIG\machine.config