How to use ASP.NET 4.8 ConfigBuilders with system.serviceModel section of web.config

Question

I have an ASP.NET 4.8 app that I am trying to integrate configuration builders into. I have installed the NuGet package Microsoft.Configuration.ConfigurationBuilders.Environment and added the required sections to Web.config (heavily truncated here).

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <section name="configBuilders" type="System.Configuration.ConfigurationBuildersSection, System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" restartOnExternalChanges="false" requirePermission="false"/>
  </configSections>

  <configBuilders>
    <builders>
      <add name="EnvironmentExpand" mode="Expand" type="Microsoft.Configuration.ConfigurationBuilders.EnvironmentConfigBuilder, Microsoft.Configuration.ConfigurationBuilders.Environment" />
    </builders>
  </configBuilders>

  <system.serviceModel configBuilders="EnvironmentExpand">
....
  </system.serviceModel>
</configuration>

When I run the application I get an HTTP 500 response from every action, with the message Unrecognized attribute 'configBuilders'. Intellisense in Visual Studio also highlights configBuilders and says The configBuilders attribute is not allowed.

If I remove the configBuilders attribute from system.serviceModel the application runs correctly although of course none of the placeholders in that section are expanded.

If I remove the configBuilders attribute from system.serviceModel and add it to another section, for instance connectionStrings, the application runs and the placeholders in the connectionStrings section are replaced.

Clearly there's something different about the system.serviceModel section but I don't understand what or how I can work around it so that I can replace placeholders in there.

Answer 1

If you look at your machine.config, you'll see that system.serviceModel is a sectionGroup and not a section. ConfigurationBuilders only apply at the section level. WCF and ASP.Net for better or worse have their large configuration divided into multiple sections.