Transform web.config

By Vijay Ramakrishnan and Luke Latham

Transformations to the web.config file can be applied automatically when an app is published based on:

These transformations occur for either of the following web.config generation scenarios:

  • Generated automatically by the Microsoft.NET.Sdk.Web SDK.
  • Provided by the developer in the content root of the app.

Build configuration

Build configuration transforms are run first.

Include a web.{CONFIGURATION}.config file for each build configuration (Debug|Release) requiring a web.config transformation.

In the following example, a configuration-specific environment variable is set in web.Release.config:

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <location>
    <system.webServer>
      <aspNetCore>
        <environmentVariables xdt:Transform="InsertIfMissing">
          <environmentVariable name="Configuration_Specific" 
                               value="Configuration_Specific_Value" 
                               xdt:Locator="Match(name)" 
                               xdt:Transform="InsertIfMissing" />
        </environmentVariables>
      </aspNetCore>
    </system.webServer>
  </location>
</configuration>

The transform is applied when the configuration is set to Release:

dotnet publish --configuration Release

The MSBuild property for the configuration is $(Configuration).

Profile

Profile transformations are run second, after Build configuration transforms.

Include a web.{PROFILE}.config file for each profile configuration requiring a web.config transformation.

In the following example, a profile-specific environment variable is set in web.FolderProfile.config for a folder publish profile:

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <location>
    <system.webServer>
      <aspNetCore>
        <environmentVariables xdt:Transform="InsertIfMissing">
          <environmentVariable name="Profile_Specific" 
                               value="Profile_Specific_Value" 
                               xdt:Locator="Match(name)" 
                               xdt:Transform="InsertIfMissing" />
        </environmentVariables>
      </aspNetCore>
    </system.webServer>
  </location>
</configuration>

The transform is applied when the profile is FolderProfile:

dotnet publish --configuration Release /p:PublishProfile=FolderProfile

The MSBuild property for the profile name is $(PublishProfile).

If no profile is passed, the default profile name is FileSystem and web.FileSystem.config is applied if the file is present in the app's content root.

Environment

Environment transformations are run third, after Build configuration and Profile transforms.

Include a web.{ENVIRONMENT}.config file for each environment requiring a web.config transformation.

In the following example, a environment-specific environment variable is set in web.Production.config for the Production environment:

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <location>
    <system.webServer>
      <aspNetCore>
        <environmentVariables xdt:Transform="InsertIfMissing">
          <environmentVariable name="Environment_Specific" 
                               value="Environment_Specific_Value" 
                               xdt:Locator="Match(name)" 
                               xdt:Transform="InsertIfMissing" />
        </environmentVariables>
      </aspNetCore>
    </system.webServer>
  </location>
</configuration>

The transform is applied when the environment is Production:

dotnet publish --configuration Release /p:EnvironmentName=Production

The MSBuild property for the environment is $(EnvironmentName).

When publishing from Visual Studio and using a publish profile, see Visual Studio publish profiles for ASP.NET Core app deployment.

The ASPNETCORE_ENVIRONMENT environment variable is automatically added to the web.config file when the environment name is specified.

Custom

Custom transformations are run last, after Build configuration, Profile, and Environment transforms.

Include a {CUSTOM_NAME}.transform file for each custom configuration requiring a web.config transformation.

In the following example, a custom transform environment variable is set in custom.transform:

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <location>
    <system.webServer>
      <aspNetCore>
        <environmentVariables xdt:Transform="InsertIfMissing">
          <environmentVariable name="Custom_Specific" 
                               value="Custom_Specific_Value" 
                               xdt:Locator="Match(name)" 
                               xdt:Transform="InsertIfMissing" />
        </environmentVariables>
      </aspNetCore>
    </system.webServer>
  </location>
</configuration>

The transform is applied when the CustomTransformFileName property is passed to the dotnet publish command:

dotnet publish --configuration Release /p:CustomTransformFileName=custom.transform

The MSBuild property for the profile name is $(CustomTransformFileName).

Prevent web.config transformation

To prevent transformations of the web.config file, set the MSBuild property $(IsWebConfigTransformDisabled):

dotnet publish /p:IsWebConfigTransformDisabled=true

Additional resources