Upgrade Azure App Service Deployment task to v4

Task 'Azure App Service deploy' version 3 (AzureRmWebAppDeployment@3) is deprecated

Azure release pipeline

Yes, this is not a post about the Sitecore platform as such but as it is related to one of my Sitecore projects it might be related to (many) more. For a Sitecore website deployed in Azure PAAS we are using Azure DevOps to deploy and we recently noticed in the release pipeline that some stages gave warnings - although they still succeeded. 

The warnings said the Azure App Service deploy task is deprecated and we should use the newer version:

Task 'Azure App Service deploy' version 3 (AzureRmWebAppDeployment@3) is deprecated
The AzureRmWebAppDeployment@3 task is deprecated, please use a newer version of the AzureRmWebAppDeploy...

So I checked the release pipeline and decided to "upgrade" the related tasks called AzureRmWebAppDeployment from v3 to v4. It looked pretty simple - just a few minor changes in the configuration and we were set to go. 

As a test I created a new release and the deployment steps seemed to work but our Unicorn sync failed with a disturbing message: the path /unicorn.aspx was not found. When we checked the files on the server with the App Service Editor we noticed the file wasn't there.. actually, almost all files were gone. 

Not knowing what had happened I redeployed the stage to see if it was some temporary issue. The second attempt however failed rather quickly: An error was encountered when processing operation 'Create File' on 'C:\home\site\wwwroot\ApplicationInsights.config. Was something really wrong with this v4? I reversed the task back to v3 and tried again, but the same error appeared. So it was not the deploy task but probably the Azure instance itself. 

Next attempt was to try and create a config file manually with the App Service Editor. Strangely that failed as well (error 409). Clearly the Web App was not behaving as expected but didn't show any errors, nor issues in the resource health. It was when I checked the Advance Tools that I finally started to get an idea of the issue. 

When opening Kudu I got this warning:

So I start searching what this WEBSITE_RUN_FROM_PACKAGE means. I noticed that this environment variable was indeed created. When I delete it, I can create files again. At that point it was time to read the documentation 🙂

I found the readme files for both version 3 and version 4 of the Azure App Service Deployment task and especially that last one was interesting as it did explain about this RunFromPackage.

RunFromPackage

Creates the same deployment package as Zip Deploy. However, instead of deploying files to the wwwroot folder, the entire package is mounted by the Functions runtime. With this option, files in the wwwroot folder become read-only.

Apparently, by default (when 'Select deployment method' is not checked) the task tries to select the appropriate deployment technology given the input package, app service type and agent OS. Maybe it was because we deploy zip files (especially for serialization files this is much faster) but Azure clearly thought it had to use the RunFromPackage. This created the environment variable causing our Web App to set the wwwroot read-only.  Problem found!

To fix it, we had to set the deployment method specifically for all the deploy steps in all stages.  

 Once we removed the WEBSITE_RUN_FROM_PACKAGE environment variable again and deployed with the deployment method set everywhere all was working fine and we have no more warnings.