Archives de catégorie : Container

Fail to pull Windows Core/Nano Server container images with Docker for Windows ‘unknown blob’

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During my last session preparation, I switched Docker for Windows to use Windows containers, to be honest I don’t have use it for some times (my nested virtualized Windows Server 2016 do the job) and I had the following error when downloading the microsoft/nanoserver image : unknow blob

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The issue may be that your Docker for Windows daemon is not completely switch to Windows container. So execute the following line to switch it : & ‘C:\Program Files\Docker\Docker\DockerCli.exe’ –SwitchDaemon

Then pull your image again and things should work :

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Fail to run a new ASP.NET Core solution with Docker in Visual Studio 2017

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Sometimes you want to make a demo to a good friend of you about Docker support in Visual Studio 2017. So your start Visual Studio 2017, create a blank ASP.NET Core (Docker support enabled), press F5 to run the application but things are not really happening like your want. In my case, I had the following message :

The specified framework ‘Microsoft.NETCore.App’, version ‘1.1.2’ was not found.
  – Check application dependencies and target a framework version installed at:
      /usr/share/dotnet/shared/Microsoft.NETCore.App
  – The following versions are installed:
      1.1.1
  – Alternatively, install the framework version ‘1.1.2’.

The issue comes from the fact that Visual Studio 2017 builds a project based on .NET Core 1.1.2 but your Docker image only supports .NET Core 1.1.1 ‘(see message). Why your image doesn’t support 1.1.2 ? Maybe simply because your image is outdated with no support for 1.1.2. So the trick is quite easy and it consists to execute the pull again the image to force Docker to update the base image :

docker pull microsoft/aspnetcore:1.1

This should solve your issue after several minutes of downloading the updated image layer.

Docker ASP.NET MVC image creation issue ‘GetFileAttributesEx : The system cannot find the path specified’

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When using Visual Studio 2017 and trying to create a Docker image for your ASP.NET web app from the standard microsoft\aspnet image (or another image), you may have the following error message : GetFileAttributesEx bin\Release\PublishOutput : The system cannot find the path specified

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This error is caused by the .dockerignore file generated by Visual Studio 2017 (more information on .dockerignore file : https://docs.docker.com/engine/reference/builder/#dockerignore-file).

How to solve the issue

  1. Open and edit the .dockerignore file located at the root of your Visual Studio project
  2. Remove the first line with the ‘*’ (this is the guilty line !)
  3. Save the modified .dockerignore file
  4. Re execute your docker build command (ex : docker build –t <your tag> .)

Original Visual Studio 2017 .dockerignore file :

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The corrected .dockerignore file :

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Check your web app to know if everything works fine

  1. First, you won’t be able to use the URL http://localhost, you need the IP address of the container. To find it, execute this command in Powershell :

    2. docker inspect -f « {{ .NetworkSettings.Networks.nat.IPAddress }} » ncit_liasse

  2. Open your favorite browser and enter the URL http//<your ip address> to show you web app shining

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More documentation on the use of this image at https://hub.docker.com/r/microsoft/aspnet/

Useful documentation on how to migrate an ASP.NET MVC application to Docker : https://docs.microsoft.com/en-us/aspnet/mvc/overview/deployment/docker-aspnetmvc

Now enjoy migrating your ASP.NET MVC web apps to Docker containers !