Nick's .NET Travels

Continually looking for the yellow brick road so I can catch me a wizard....

Debugging ASP.NET Core with Visual Studio and Docker Desktop

With Visual Studio 2019 hot off the press I’ve been experimenting with a few of the new project templates and the improvements that have been made in Visual Studio. In this post I’m going to cover how to solve a particularly annoying problem I encountered when attempting to run and debug an ASP.NET Core 3 application from within Visual Studio, hosted within a Docker image. I’ll walk through the whole process of creating the new project and the issue I ran into when first attempting to debug the application.

When you launch Visual Studio 2019, or go to create a new project, you’ll see the Create a new project dialog. We’re going to select the ASP.NET Core Web Application template.

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Next we need to provide the standard project information such as name and location.

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The next stage is to provide more information about how the template should be configured. Here we’re selecting the API template from the left of the screen, and checking both the https and the Enable Docker Support.

Note: At this point if you haven’t already downloaded and installed Docker Desktop, do it now. It’s a half Gb or so download, so not small, and may take a while based on your network bandwidth.

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After creating the template, you’ll see that there are a number of options available to us in order to run the application. We’re going to proceed with the Docker option.

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If you haven’t already, make sure you have launched Docker Desktop, otherwise you’ll see the following warning in Visual Studio when you attempt to run the application.

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Unless you’ve previously setup Docker Desktop you’ll most likely see the following error. Essentially you need to award Docker Desktop access to a drive in order to create images etc.

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Right-click the Docker icon in the tray and select Settings

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Under Shared Drives tab, check the local drives you want to make available to Docker Desktop.

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When you click Apply you’ll be prompt to authenticate. It will detect the credentials of the current user, which for me is an Azure Active Directory user.

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Important: Unfortunately after providing my password and clicking OK, Docker Desktop decides that it will uncheck the drive that I had selected. This seems to be a common issue, raised by a couple of different people online. Anyhow, the following steps demonstrate how to setup a different account and using it to allow Docker Desktop to access the drive. Whilst a bit hacky, this does seem to be the only work around for this issue.

To setup a new account launch Settings, click Other users and then click the + button under Other users.

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When prompted to enter email or phone number, instead click the “I don’t have this persons’ sign-in information” option.

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Next, click the “Add a user without a Microsoft account” option

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When prompted, enter username, password and some security questions. Next you need to change this user to be an administrator, so expand out the account under Other users and click Change account type.

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Change Account type to Administrator

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Return now to Docker Desktop and enter the new account as part of setting up the shared drive. You shouldn’t see any further issues within the Docker Desktop application.

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Attempting to run the application from within Visual Studio again reveals an error, this time complaining it doesn’t have authority to crLeate or adjust folders (including creating files). 

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Locate the folder indicated in the error message, right-click on the folder and select Properties. From the Security tab, click Edit.

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Add the local account you just created and make sure it’s assigned all permissions.

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You may need to repeat this process for 2 or 3 folders that Docker Desktop requires access to, and in some case assigning permissions can take a minute or two. Once done, your application will be launched from within a Docker image, with the Visual Studio debugger attached.

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