When you are having different people working on one project remotely you will get some problem with web.config, as everybody was having different version of web.config. So at that time once you check in your web.config with your latest changes the other people have to get latest that web.config and made some specific changes as per their local environment. Most of people who have worked things from remotely has faced that problem. I think most common example would be connection string and app settings changes.

For this kind of situation this will be a best solution. We can divide particular section of web.config into the multiple files. For example we could have separate ConnectionStrings.config file for connection strings and AppSettings.config file for app settings file.

Most of people does not know that there is attribute called ‘configSource’ where we can  define the path of external config file and it will load that section from that external file. Just like below.

<configuration>
 <appSettings configSource="AppSettings.config"/>
 <connectionStrings configSource="ConnectionStrings.config"/>
</configuration>

And you could have your ConnectionStrings.config file like following.

<connectionStrings>
  <add name="DefaultConnection" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=aspnet-WebApplication1-20120523114732;Integrated Security=True"
    providerName="System.Data.SqlClient" />
</connectionStrings>

Same way you have another AppSettings.Config file like following.

<appSettings>
  <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
  <add key="ValidationSettings:UnobtrusiveValidationMode" value="WebForms" />
</appSettings>