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Visual Studio Tools for Docker with ASP.NET Core This article walks through using Visual Studio 2017 tooling and Docker for Windows to containerize an ASP.NET Core application. Docker,ASP.NET Core,Visual Studio,container spboyer scaddie wpickett 09/26/2017 article asp.net-core aspnet 1f3b9a68-4dea-4b60-8cb3-f46164eedbbf publishing/vs-tools-for-docker

Visual Studio Tools for Docker

Microsoft Visual Studio 2017 with Docker for Windows supports building, debugging, and running .NET Framework and .NET Core web and console applications using Windows and Linux containers.

Prerequisites

Installation and setup

Install Microsoft Visual Studio 2017 with the .NET Core workload.

For Docker installation, review the information at Docker for Windows: What to know before you install and install Docker For Windows.

A required configuration is to setup Shared Drives in Docker for Windows. The setting is required for the volume mapping and debugging support.

Right-click the Docker icon in the System Tray, click Settings, and select Shared Drives. Select the drive where Docker will store your files and apply changes.

Shared Drives

Create an ASP.NET Web Application and add Docker Support

Using Visual Studio, create a new ASP.NET Core Web Application. When the application is loaded, either select Add Docker Support from the Project Menu or right-click the project from the Solution Explorer and select Add > Docker Support.

Project Menu

Project Add Docker Support

Project Context Menu

Right-Click Add Docker Support

When you add Docker support to your project, you can choose either Windows or Linux containers. (The Docker host must be running the same container type. If you need change the container type in the running Docker instance, right-click the Docker icon in the System Tray, and choose Switch to Windows containers or Switch to Linux containers.)

The following files are added to the project:

  • Dockerfile: the Docker file for ASP.NET Core applications is based on the microsoft/aspnetcore image. This image includes the ASP.NET Core NuGet packages, which have been pre-jitted improving startup performance. When building .NET Core Console Applications, the Dockerfile FROM will reference the most recent microsoft/dotnet image.
  • docker-compose.yml: base Docker Compose file used to define the collection of images to be built and run with docker-compose build/run.
  • docker-compose.dev.debug.yml: additional docker-compose file with for iterative changes when your configuration is set to debug. Visual Studio will call -f docker-compose.yml -f docker-compose.dev.debug.yml to merge these together. This compose file is used by Visual Studio development tools.
  • docker-compose.dev.release.yml: additional Docker Compose file to debug your release definition. It will volume mount the debugger so it doesn't change the contents of the production image.

The docker-compose.yml file contains the name of the image that is created when project is run.

version '2'

services:
  hellodockertools:
    image:  user/hellodockertools${TAG}
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "80"

In this example, image: user/hellodockertools${TAG} generates the image user/hellodockertools:dev when the application is run in Debug mode and user/hellodockertools:latest in Release mode respectively.

You will want to change the user to your Docker Hub username if you plan to push the image to the registry. For example, spboyer/hellodockertools, or change to your private registry URL privateregistry.domain.com/ depending on your configuration.

Debugging

Select Docker from the debug drop-down in the toolbar and use F5 to start debugging the application.

  • The microsoft/aspnetcore image is acquired (if not already in your cache)
  • ASPNETCORE_ENVIRONMENT is set to Development within the container
  • PORT 80 is EXPOSED and mapped to a dynamically assigned port for localhost. The port is determined by the docker host and can be queried with docker ps.
  • Your application is copied to the container
  • Default browser is launched with the debugger attached to the container, using the dynamically assigned port.

The resulting Docker image built is the dev image of your application with the microsoft/aspnetcore images as the base image.

Note: The dev image is empty of your app contents as Debug configurations use volume mounting to provide the iterative experience. To push an image, use the Release configuration.

REPOSITORY                  TAG         IMAGE ID            CREATED         SIZE
spboyer/hellodockertools    dev         0b6e2e44b3df        4 minutes ago   268.9 MB
microsoft/aspnetcore        1.0.1       189ad4312ce7        5 days ago      268.9 MB

The application is running using the container, which you can see by running the docker ps command.

CONTAINER ID        IMAGE                          COMMAND               CREATED             STATUS              PORTS                   NAMES
3f240cf686c9        spboyer/hellodockertools:dev   "tail -f /dev/null"   4 minutes ago       Up 4 minutes        0.0.0.0:32769->80/tcp   hellodockertools_hellodockertools_1

Edit and Continue

Changes to static files and/or razor template files (.cshtml) are automatically updated without the need of a compilation step. Make the change, save, and tap refresh in the browser to view the update.

Modifications to code files require compiling and a restart of Kestrel within the container. After making the change, use CTRL + F5 to perform the process and start the application within the container. The Docker container is not rebuilt or stopped; using docker ps in the command line, you can see that the original container is still running as of 10 minutes ago.

CONTAINER ID        IMAGE                          COMMAND               CREATED             STATUS              PORTS                   NAMES
3f240cf686c9        spboyer/hellodockertools:dev   "tail -f /dev/null"   10 minutes ago      Up 10 minutes       0.0.0.0:32769->80/tcp   hellodockertools_hellodockertools_1

Publishing Docker images

Once you have completed the develop and debug cycle of your application, the Visual Studio Tools for Docker will help you create the production image of your application. Change the debug dropdown to Release and build the application. The tooling will produce the image with the :latest tag which you can push to your private registry or Docker Hub.

Using the docker images command, you can see the list of images.

REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
spboyer/hellodockertools   latest              8184ae38ba91        5 seconds ago       278.4 MB
spboyer/hellodockertools   dev                 0b6e2e44b3df        About an hour ago   268.9 MB
microsoft/aspnetcore       1.0.1               189ad4312ce7        5 days ago          268.9 MB

There may be an expectation for the production or release image to be smaller in size by comparison to the dev image; however, through the use of the volume mapping, the debugger and application were actually being run from your local machine and not within the container. The latest image has packaged the entire application code needed to run the application on a host machine, therefore the delta is the size of your application code.