Azure Web App deploy: Web Deploy cannot modify the file on the destination because it is locked by an external process

Question

I am using the "Azure Web App Deployment" build step in VSTS to publish an ASP.NET Core API to an Azure Web App:

Occasionally, this step breaks with the following error:

[error]Microsoft.Web.Deployment.DeploymentDetailedClientServerException: Web Deploy cannot modify the file 'MyProject.Api.exe' on the destination because it is locked by an external process. In order to allow the publish operation to succeed, you may need to either restart your application to release the lock, or use the AppOffline rule handler for .Net applications on your next publish attempt. Learn more at: http://go.microsoft.com/fwlink/?LinkId=221672#ERROR_FILE_IN_USE.

This GitHub issue raises the same issue, but there is no suggested solution using the Azure Web App Deployment build step.

Answer 1

As per a separate thread in the Microsoft Github repo here, there's a hacky workaround where if you add the following key to the Azure Appsettings, it can help resolve the locked file deployment error:

MSDEPLOY_RENAME_LOCKED_FILES = 1 

I'm not sure how long this appsetting hack will be supported, but it did help solve the issue for me personally.

Answer 2

I was struggling with the same locking issue.
There are now a new Tasks (in Preview) that you can add for starting and stopping the App Service:

Add a stop task before deployment and a start task after the deployment.

This did the trick for me.