File Transform task fails to transform XML configurations on zipped package - azure

Question

I'm working on Release pipeline, which will perform transformation on App Service Worker configs, then will publish workers + web application.
My input package is a zip package produced out of MsBuild publish (from ASP.NET build pipeline).
...\PackageTmp\app_data\jobs\triggered\BillingWorker\App.Prod.config
...\PackageTmp\app_data\jobs\triggered\BillingWorker\App.Test.config
...\PackageTmp\app_data\jobs\triggered\BillingWorker\BillingWorker.exe.config
...\PackageTmp\app_data\jobs\triggered\EtlWorker\App.Prod.config
...\PackageTmp\app_data\jobs\triggered\EtlWorker\App.Test.config
...\PackageTmp\app_data\jobs\triggered\EtlWorker\EtlWorker.exe.config
...\PackageTmp\Web.config
...\PackageTmp\Web.Test.config
...\PackageTmp\Web.Prod.config
...\PackageTmp\many other files
Transformation of Web.config is done correctly by Publish to Azure Web App task. However, workers configs aren't transformed automatically, so I added a File Transform task with following config:
This step doesn't work and here is the output:
2019-08-14T15:41:01.1435779Z ##[section]Starting: File Transform: config
2019-08-14T15:41:01.1576716Z ==============================================================================
2019-08-14T15:41:01.1576853Z Task : File transform
2019-08-14T15:41:01.1576932Z Description : Replace tokens with variable values in XML or JSON configuration files
2019-08-14T15:41:01.1576994Z Version : 1.156.0
2019-08-14T15:41:01.1600786Z Author : Microsoft Corporation
2019-08-14T15:41:01.1600885Z Help : https://learn.microsoft.com/azure/devops/pipelines/tasks/utility/file-transform
2019-08-14T15:41:01.1600986Z ==============================================================================
2019-08-14T15:41:01.6339900Z ##[warning]Unable to apply transformation for the given package. Verify the following.
2019-08-14T15:41:01.6351367Z ##[warning]Unable to apply transformation for the given package. Verify the following.
2019-08-14T15:41:01.8369297Z Initiated variable substitution in config file :
...
... many lines about variable subsitution
...
This output looks wrong, as it produces warning without declared explanation. How to workaround this warning?

Answer 1

The problem is that File Transform task strongly relies on names of both files - the one being transformed and the one containing transformation rules. Strict naming convention is required which can be described in following words:
A template named Name.xml can be transformed only by files named Name.Debug.xml, Name.Release.xml, and more general - Name.{anything-here}.xml.
What's happening here is that App.config file is renamed to {YourApplicationName}.exe.config during build thus the tranformation using App.Debug.config fails.
I see 2 workarounds:
1. Preserve the original name App.config
a. In a project file, set App.config file's property to Copy to output directory: Copy always
b. Setup "File Transform task" with args -transform *.Debug.config -xml *.config -result {YourApplicationName}.exe.config
c (optional). If you didn't specify -result in task, you need to setup another task to rename App.config to {YourApplicationName}.exe.config after the transformation has finished (for example a Command Line task with command copy App.config {YourApplicationName}.exe.config /Y)
2. Write custom transformator script
a. Unzip package into temp folder
b. Transform file using Powershell (make use of Microsoft.Web.XmlTransform.dll installed on agent)
c. Zip again and replace the original zip.

Answer 2

The native step in the official task doesn't support transformation in zip files. You can use another task for do it before the deploy task.
I used this and it worked fine to me:
https://marketplace.visualstudio.com/items?itemName=solidify-labs.vsts-task-tokenize-in-archive