Dev Azure Pipeline Web Config Transform

The web.config transform appears at first glance to be somewhat orphaned in Azure DevOps. If you are deploying to a WebApp then the pipeline wizard will probably have given you this snippet for your Build step:

- task: VSBuild@1
solution: '$(solution)'
msbuildArgs: '/p:DeployOnBuild=true /p:WebPublishMethod=Package /p:PackageAsSingleFile=true /p:SkipInvalidConfigurations=true /p:DesktopBuildPackageLocation="$(build.artifactStagingDirectory)\" /p:DeployIisAppPath="Default Web Site"'
platform: '$(buildPlatform)'
configuration: '$(buildConfiguration)'

To run config transforms you can add the additional parameter /p:TransformConfigFile=true to your msbuildArgs.

The replacement, of course, is the independent FileTransform task (which can also work within zip files). But once your site is packaged the Web.Release.Config is left behind; so you have to run the FileTransform task before, not after, the build step. (Similarly the WebAppDeployment task can't transform a Web.Release.config that isn't inside the package).

Slightly magically, the default parameter for the FileTransform is exactly what you typically want for web.Release.config transforms:

#xmlTransformationRules: '-transform **\*.Release.config -xml **\*.config-transform **\*.$(Release.EnvironmentName).config -xml **\*.config' # Optional

FileTransform can also do variable substitution, and you can have multiple FileTransform steps in your pipeline. I also like to see some diagnostic feedback so I include script step to show the xml transform result. But I put it before variable substitution, because the variables often include secrets:

- task: FileTransform@1
displayName: Transform Release.Config
folderPath: '$(System.DefaultWorkingDirectory)/Ui/'
enableXmlTransform: true
xmlTransformationRules: -transform **/*.Release.config -xml **/*.config

- task: PowerShell@2
displayName: "Confirm web.config transform"
targetType: 'inline'
script: 'cat $env:System_DefaultWorkingDirectory/Ui/web.config'
errorActionPreference: 'continue'

- task: FileTransform@1
displayName: Variable substitution *.config
folderPath: '$(System.DefaultWorkingDirectory)/Ui/'
fileType: 'xml'
targetFiles: '**/*.config'

- task: VSBuild@1