Using Docker with .NET Core

Posted by minati biswal on September 9th, 2019

.NET Core is modular and faster when compared to the .NET framework and helps in running applications side by side, where each application is running its own set of CLR libraries and runtime. This makes it perfect for running on Docker containers. The image of .NET Core is far smaller when compared to the image having the .NET framework installed. .NET Core uses a Windows Nano Server or Linux image, which is a lot smaller than the Windows service core image. As .NET Core runs cross-platform, we can also create Docker images of other platforms and run applications on them.

With Visual Studio 2017, we can choose Docker while creating a .NET Core or ASP.NET Core project, and it auto scaffolds the Docker files and sets up the basic configuration to run applications on Docker. The following screenshot shows the Docker options available in Visual Studio 2017 to provision Docker containers:
Alternatively, if the project is already created, we can add Docker support by right-clicking on the .NET Core project and clicking on the Add | Docker Support option.

Once we create or enable Docker support in our application, it creates the Docker files in our project and also adds another project, named docker-compose, as follows:

The docker-compose project contains set of YAML (.yml) files that contain the configuration related to the application hosted in the container and a reference to the path of the Dockerfile created for the project when Docker support was added. Here is the sample docker-compose.yml file that contains two services having details such as the image name, dockerfile path, and so on. This file is from the sample application we discussed previously:

version: '1' 

 services: 

  vendor.api: 

    image: vendor.api 

    build: 

      context: . 

      dockerfile: srcmicroservicesVendorVendor.APIDockerfile 

   identity.api: 

    image: identity.api 

    build: 

      context: . 

      dockerfile: srcmicroservicesAuthServerIdentity.AuthServerDockerfile 

The following is the content of the Dockerfile residing inside the Vendor.API project we created in the sample application above:

FROM microsoft/aspnetcore:2.0-nanoserver-1709 AS base 

WORKDIR /app 

EXPOSE 80 

 FROM microsoft/aspnetcore-build:2.0-nanoserver-1709 AS build 

WORKDIR /src    

COPY *.sln ./ 

COPY src/microservices/Vendor/Vendor.API/Vendor.API.csproj src/microservices/Vendor/Vendor.API/ 

RUN dotnet restore 

COPY . . 

WORKDIR /src/src/microservices/Vendor/Vendor.API 

RUN dotnet build -c Release -o /app 

 FROM build AS publish 

RUN dotnet publish -c Release -o /app 

FROM base AS final 

WORKDIR /app 

COPY --from=publish /app . 

ENTRYPOINT ["dotnet", "Vendor.API.dll"] 

 The preceding Dockerfile starts referencing a base image Microsoft/aspnetcore:2.0-nano server-1709 that will be used to create a Docker container. The COPY command is the actual path where the project files reside. It will then use dotnet CLI commands such as dotnet restore to restore all the NuGet packages inside the container, dotnet build to build the application, and dotnet publish to build and publishes the compiled output into a publish folder inside the container.

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