Building an ASP.Net Core Web App Docker image

 In this post we shall see how to create a basic Asp.Net core Hello World App and package it into a Docker image. We will deploy the image as a Docker container and execute the Asp.Net Core application from Docker.

First let us start by creating an Asp.Net Core application using Visual Studio 2019

Choose Web Application (MVC), make sure to check the Enable Docker Support and select Windows. This will automatically create the Dockerfile and .dockerignore files for the Application.

We will name the project HelloCore

The project gets created as follows, notice that the Dockerfile is automatically created.

The .dockerignore file has the following exclusions which will not be included in the Docker image.
**/.classpath

**/.dockerignore

**/.env

**/.git

**/.gitignore

**/.project

**/.settings

**/.toolstarget

**/.vs

**/.vscode

**/*.*proj.user

**/*.dbmdl

**/*.jfm

**/azds.yaml

**/bin

**/charts

**/docker-compose*

**/Dockerfile*

**/node_modules

**/npm-debug.log

**/obj

**/secrets.dev.yaml

**/values.dev.yaml

LICENSE

README.md

Let’s make a small update to the message displayed in the Home page.
We will update the Home/Index view to display a welcome message as follows
@{

    ViewData["Title"] = "Home Page";

}

<div class="text-center">

    <h3 class="display-4">Welcome to Asp.Net Core Docker</h3>   

</div>

When we build the docker image, it will try to restore the NuGet packages for which it needs to download the packages from internet. If you are in a corporate firewall behind the proxy then we need to set the proxy congifuration so that it can download and restore the packages.
Add the below 2 lines to configure proxy for http & https with the proxy server and credentials

WORKDIR /src

COPY ["HelloCore.csproj", ""]

ARG HTTP_PROXY="http://<username>:<password>@<proxyserver>:8080"

ARG HTTPS_PROXY="http://<username>:<password>@<proxyserver>:8080"

RUN dotnet restore "./HelloCore.csproj"

We can build the docker image for the Hello World Asp.Net Core project as follows

>docker build -t hellocore .

Sending build context to Docker daemon  4.395MB

Step 1/16 : FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-nanoserver-1803 AS base

3.1-nanoserver-1803: Pulling from dotnet/core/aspnet

e46172273a4e: Pull complete

4e0aad55be14: Pull complete

84b221f7a453: Pull complete

1fe099edc738: Pull complete

a091df200146: Pull complete

92ed030ab670: Pull complete

fc1b71d39b32: Pull complete

773dcb962d4f: Pull complete

Digest: sha256:3b4383b72b53a00895267571d08e9591eab1b914f35b2c2c4a2413d178eca089

Status: Downloaded newer image for mcr.microsoft.com/dotnet/core/aspnet:3.1-nanoserver-1803

 ---> 22613f6353d7

Step 2/16 : WORKDIR /app

 ---> Running in deeef4b1b75a

Removing intermediate container deeef4b1b75a

 ---> 37555b9de604

Step 3/16 : EXPOSE 80

 ---> Running in c8ff0e885975

Removing intermediate container c8ff0e885975

 ---> 74425e01227b

Step 4/16 : FROM mcr.microsoft.com/dotnet/core/sdk:3.1-nanoserver-1803 AS build

3.1-nanoserver-1803: Pulling from dotnet/core/sdk

e46172273a4e: Already exists

4e0aad55be14: Already exists

d4ab8b1aa41b: Pull complete

6a78bc115e4e: Pull complete

b17f9e12a86e: Pull complete

f54f0fc0b6ad: Pull complete

d04f75b18a67: Pull complete

4d403afe1106: Pull complete

1b87aeb9ca18: Pull complete

Digest: sha256:32929dc0b6d20a038c4bc082ccce9dcd1e87f3150fcabdc2f9430853c4a040d0

Status: Downloaded newer image for mcr.microsoft.com/dotnet/core/sdk:3.1-nanoserver-1803

 ---> 72e582217dbf

Step 5/16 : WORKDIR /src

 ---> Running in d9077abc552c

Removing intermediate container d9077abc552c

 ---> 18c5c795d2ec

Step 6/16 : COPY ["HelloCore.csproj", ""]

 ---> 1bc261605621

Step 7/16 : RUN dotnet restore "./HelloCore.csproj"

 ---> Running in 5cb3675173b4

  Restore completed in 740.01 ms for C:\src\HelloCore.csproj.

Removing intermediate container 5cb3675173b4

 ---> d98146917164

Step 8/16 : COPY . .

 ---> ae9f3bbe1b66

Step 9/16 : WORKDIR "/src/."

 ---> Running in 8c7f8aa6b6b7

Removing intermediate container 8c7f8aa6b6b7

 ---> 483b78d9da18

Step 10/16 : RUN dotnet build "HelloCore.csproj" -c Release -o /app/build

 ---> Running in 740cb7897afb

Microsoft (R) Build Engine version 16.4.0-preview-19529-02+0c507a29b for .NET Core

Copyright (C) Microsoft Corporation. All rights reserved.

 

  Restore completed in 46.26 ms for C:\src\HelloCore.csproj.

  You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview

  HelloCore -> C:\app\build\HelloCore.dll

  HelloCore -> C:\app\build\HelloCore.Views.dll

 

Build succeeded.

    0 Warning(s)

    0 Error(s)

 

Time Elapsed 00:00:08.23

Removing intermediate container 740cb7897afb

 ---> d4a1042d579c

Step 11/16 : FROM build AS publish

 ---> d4a1042d579c

Step 12/16 : RUN dotnet publish "HelloCore.csproj" -c Release -o /app/publish

 ---> Running in 9bdcd9164c5f

Microsoft (R) Build Engine version 16.4.0-preview-19529-02+0c507a29b for .NET Core

Copyright (C) Microsoft Corporation. All rights reserved.

 

  Restore completed in 46.36 ms for C:\src\HelloCore.csproj.

  You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview

  HelloCore -> C:\src\bin\Release\netcoreapp3.1\HelloCore.dll

  HelloCore -> C:\src\bin\Release\netcoreapp3.1\HelloCore.Views.dll

  HelloCore -> C:\app\publish\

Removing intermediate container 9bdcd9164c5f

 ---> d80159b14f36

Step 13/16 : FROM base AS final

 ---> 74425e01227b

Step 14/16 : WORKDIR /app

 ---> Running in 352109c49f01

Removing intermediate container 352109c49f01

 ---> a2776878bd59

Step 15/16 : COPY --from=publish /app/publish .

 ---> 8f6a898955a7

Step 16/16 : ENTRYPOINT ["dotnet", "HelloCore.dll"]

 ---> Running in 5b8ae4f5c5d6

Removing intermediate container 5b8ae4f5c5d6

 ---> c6d171b63436

Successfully built c6d171b63436

Successfully tagged hellocore:latest

 

Once the build is completed run the image ls command to make sure that the image is created.

>docker image ls

REPOSITORY                             TAG                   IMAGE ID            CREATED             SIZE

hellocore                              latest                c6d171b63436        2 minutes ago       472MB

mcr.microsoft.com/dotnet/core/sdk      3.1-nanoserver-1803   72e582217dbf        9 months ago        854MB

mcr.microsoft.com/dotnet/core/aspnet   3.1-nanoserver-1803   22613f6353d7        9 months ago        467MB

 

Next run the docker image and export port#7000. Map port 80 from the Docker image to port 7000 in the machine.

>docker run -d -p 7000:80 hellocore

8e73c87223090b1f36d8e5088701fcb567d8dd44d8312808270b426489917646

 

Run the container ls command to make sure that the Docker image is live and running

>docker container ls

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES

8e73c8722309        hellocore           "dotnet HelloCore.dll"   9 seconds ago       Up 7 seconds        0.0.0.0:7000->80/tcp   loving_hypatia 

To view details of the running container run the docker ps command

>docker ps

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES

8e73c8722309        hellocore           "dotnet HelloCore.dll"   17 seconds ago      Up 14 seconds       0.0.0.0:7000->80/tcp   loving_hypatia 

Open a browser and enter the address http://localhost:7000

You can see the Asp.Net core application is now running inside the docker container. Notice that the application is exposed through port# 7000, which we configured when running the Docker container.