[Visual Studio 2017](https://www.visualstudio.com/) supports building, debugging, and running ASP.NET Core apps targeting either .NET Framework or .NET Core. Both Windows and Linux containers are supported.
For Docker installation, review the information at [Docker for Windows: What to know before you install](https://docs.docker.com/docker-for-windows/install/#what-to-know-before-you-install) and install [Docker For Windows](https://docs.docker.com/docker-for-windows/install/).
**[Shared Drives](https://docs.docker.com/docker-for-windows/#shared-drives)** in Docker for Windows must be configured to support volume mapping and debugging. Right-click the System Tray's Docker icon, select **Settings...**, and select **Shared Drives**. Select the drive where Docker stores files. Select **Apply**.
The ASP.NET Core project's target framework determines the supported container types. Projects targeting .NET Core support both Linux and Windows containers. Projects targeting .NET Framework only support Windows containers.
When adding Docker support to a project, choose either a Windows or a Linux container. The Docker host must be running the same container type. To change the container type in the running Docker instance, right-click the System Tray's Docker icon and choose **Switch to Windows containers...** or **Switch to Linux containers...**.
The Visual Studio Tools for Docker don't support adding Docker to an existing ASP.NET Core project targeting .NET Framework. For ASP.NET Core projects targeting .NET Core, there are two options for adding Docker support via the tooling. Open the project in Visual Studio, and choose one of the following options:
* *.dockerignore*: Contains a list of file and directory patterns to exclude when generating a build context.
* *docker-compose.yml*: The base [Docker Compose](https://docs.docker.com/compose/overview/) file used to define the collection of images to be built and run with `docker-compose build` and `docker-compose run`, respectively.
* *docker-compose.override.yml*: An optional file, read by Docker Compose, containing configuration overrides for services. Visual Studio executes `docker-compose -f "docker-compose.yml" -f "docker-compose.override.yml"` to merge these files.
A *Dockerfile*, the recipe for creating a final Docker image, is added to the project root. Refer to [Dockerfile reference](https://docs.docker.com/engine/reference/builder/) for an understanding of the commands within it. This particular *Dockerfile* uses a [multi-stage build](https://docs.docker.com/engine/userguide/eng-image/multistage-build/) containing four distinct, named build stages:
The *Dockerfile* is based on the [microsoft/aspnetcore](https://hub.docker.com/r/microsoft/aspnetcore) image. This base image includes the ASP.NET Core NuGet packages, which have been pre-jitted to improve startup performance.
In the preceding example, `image: hellodockertools` generates the image `hellodockertools:dev` when the app runs in **Debug** mode. The `hellodockertools:latest` image is generated when the app runs in **Release** mode.
Prefix the image name with the [Docker Hub](https://hub.docker.com/) username (for example, `dockerhubusername/hellodockertools`) if the image will be pushed to the registry. Alternatively, change the image name to include the private registry URL (for example, `privateregistry.domain.com/hellodockertools`) depending on the configuration.
Select **Docker** from the debug drop-down in the toolbar, and start debugging the app. The **Docker** view of the **Output** window shows the following actions taking place:
* The *microsoft/aspnetcore* runtime image is acquired (if not already in the cache).
* The *microsoft/aspnetcore-build* compile/publish image is acquired (if not already in the cache).
* The *ASPNETCORE_ENVIRONMENT* environment variable 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 the `docker ps` command.
* The app is copied to the container.
* The default browser is launched with the debugger attached to the container using the dynamically-assigned port.
The resulting Docker image is the *dev* image of the app with the *microsoft/aspnetcore* images as the base image. Run the `docker images` command in the **Package Manager Console** (PMC) window. The images on the machine are displayed:
> The dev image lacks the app contents, as **Debug** configurations use volume mounting to provide the iterative experience. To push an image, use the **Release** configuration.
Changes to static files and Razor views are automatically updated without the need for a compilation step. Make the change, save, and refresh the browser to view the update.
Modifications to code files requires compiling and a restart of Kestrel within the container. After making the change, use CTRL + F5 to perform the process and start the app within the container. The Docker container isn't rebuilt or stopped. Run the `docker ps` command in PMC. Notice the original container is still running as of 10 minutes ago:
Once the develop and debug cycle of the app is completed, the Visual Studio Tools for Docker assist in creating the production image of the app. Change the configuration drop-down to **Release** and build the app. The tooling produces the image with the *latest* tag, which can be pushed to the private registry or Docker Hub.
> The `docker images` command returns intermediary images with repository names and tags identified as *\<none>* (not listed above). These unnamed images are produced by the [multi-stage build](https://docs.docker.com/engine/userguide/eng-image/multistage-build/) *Dockerfile*. They improve the efficiency of building the final image—only the necessary layers are rebuilt when changes occur. When the intermediary images are no longer needed, delete them using the [docker rmi](https://docs.docker.com/engine/reference/commandline/rmi/) command.
There may be an expectation for the production or release image to be smaller in size by comparison to the *dev* image. Because of the volume mapping, the debugger and app were running from the local machine and not within the container. The *latest* image has packaged the necessary app code to run the app on a host machine. Therefore, the delta is the size of the app code.
