Role and env based configurations

 <configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/">

    <sitecore role:require="Standalone or ContentManagement">

<unicorn>

And then in the web.config in 

<appSettings>

     <add key="role:define" value="ContentDelivery" />

<add key="env:define" value="$(env)"/> or hardcode the value here but htat will required config transform