.NET Core Hello World Web App and Docker

 1. Create a new web app from command line using the command: 

dotnet new web -o myWebApp

2.  Open the myWebApp.csproj file. It will have following text: 

<Project Sdk="Microsoft.NET.Sdk.Web">

     <PropertyGroup>

    <TargetFramework>net5.0</TargetFramework>

  </PropertyGroup>

</Project>

Change the target framework to netcoreapp3.1 and save the file. 

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>

    <TargetFramework>netcoreapp3.1</TargetFramework>

  </PropertyGroup>

</Project>

3. Create a dockerfile in the project in the same folder as the .csproj file. 

Enter the following text in it and save the file. 

FROM mcr.microsoft.com/dotnet/aspnet:3.1 AS base

FROM mcr.microsoft.com/dotnet/sdk:3.1 AS build

WORKDIR /src

COPY ["myWebApp.csproj", "."]  #captalisation important!!

RUN dotnet restore "./myWebApp.csproj"

COPY . .

WORKDIR "/src/."

RUN dotnet publish "myWebApp.csproj" -c Release -o /app/publish

FROM base

WORKDIR /app

COPY --from=build /app/publish .

ENTRYPOINT ["dotnet", "myWebApp.dll"]

Note 1 : The version of .NET core is taken as 3.1, which is matching to the one in .csproj file. 

2. Take care of capitalisation of file names. In the above file, if you spell "myWepApp.csproj" as "mywebapp.csproj", docker will not be able to find the file. 

4. Check that docker is runing. If not, run the Docker QuickStart Terminal .  ( I am talking this about Windows machine below 10, mine is Windows 8.1 and I require docker tool box insalled). 

If your docker is running you should get "Running" as a response to "docker-machine status default" command. 

5. Build the docker image: 

docker build -t mywebapptag . 

Here mywebapptag is the image tag and "." is the path of docker file /context. 

You should get an output like the following: 

E:\RajeshWorks\myWebApp>docker build -t mywebapptag .

Sending build context to Docker daemon  20.48kB

Step 1/12 : FROM mcr.microsoft.com/dotnet/aspnet:3.1 AS base

 ---> dd0cb488d08f

Step 2/12 : FROM mcr.microsoft.com/dotnet/sdk:3.1 AS build

 ---> 5dbfe879d2f7

Step 3/12 : WORKDIR /src

 ---> Using cache

 ---> 8aa0dcb0d5b1

Step 4/12 : COPY ["myWebApp.csproj", "."]  #captalisation important!!

 ---> Using cache

 ---> 4cfe0fcb97e9

Step 5/12 : RUN dotnet restore "./myWebApp.csproj"

 ---> Running in faacadf31de2

  Determining projects to restore...

  Restored /src/myWebApp.csproj (in 219 ms).

Removing intermediate container faacadf31de2

 ---> a4c8792fa8b1

Step 6/12 : COPY . .

 ---> 066f423bf5cd

Step 7/12 : WORKDIR "/src/."

 ---> Running in 2db699fe1c13

Removing intermediate container 2db699fe1c13

 ---> 04d5b634c493

Step 8/12 : RUN dotnet publish "myWebApp.csproj" -c Release -o /app/publish

 ---> Running in fe6064693b56

Microsoft (R) Build Engine version 16.7.2+b60ddb6f4 for .NET

Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...

  Restored /src/myWebApp.csproj (in 236 ms).

  myWebApp -> /src/bin/Release/netcoreapp3.1/myWebApp.dll

  myWebApp -> /app/publish/

Removing intermediate container fe6064693b56

 ---> dec97175c592

Step 9/12 : FROM base

 ---> dd0cb488d08f

Step 10/12 : WORKDIR /app

 ---> Using cache

 ---> 9af8e3a6945b

Step 11/12 : COPY --from=build /app/publish .

 ---> 03eba5ecb2f0

Step 12/12 : ENTRYPOINT ["dotnet", "myWebApp.dll"]

 ---> Running in 7a375a435725

Removing intermediate container 7a375a435725

 ---> 461cbdc4bee4

Successfully built 461cbdc4bee4

Successfully tagged mywebapptag:latest

SECURITY WARNING: You are building a Docker image from Windows against a non-Win

dows Docker host. All files and directories added to build context will have '-r

wxr-xr-x' permissions. It is recommended to double check and reset permissions f

or sensitive files and directories.

6. The image is now ready, you can confirm it with the command "docker ps -a" 

REPOSITORY                        TAG                 IMAGE ID            CREATED             SIZE

mywebapptag                       latest              27ee7997303a        53 seconds ago      208MB

<none>                            <none>              44b18da96e75        53 seconds ago      711MB

mcr.microsoft.com/dotnet/aspnet   3.1                 dd0cb488d08f        8 days ago          208MB

mcr.microsoft.com/dotnet/sdk      3.1                 5dbfe879d2f7        8 days ago          710MB

7. Check the ip of the docker machine, so that you may use it to browse your web site. 

"docker-machine ip default" 

=> 192.168.99.100

8. Run the docker image : 

docker run -d -p 5000:80 --name mywebappcontainer mywebapptag 

This will return you a large hex number. 

"docker container ls" command will return the following : 

CONTAINER ID   IMAGE                  COMMAND                    CREATED             STATUS              

6237a2fecded        mywebapptag         "dotnet myWebApp.dll"   2 minutes ago       Up 2 minutes

PORTS                         NAMES

0.0.0.0:5000->80/tcp   mywebappcontainer

9. Browse to the url  http://192.168.99.100:5000

You should be able to see "Hello World!". 

Note that the IP address is the one we got in step 7.