Exercise - Build a container image for your .NET microservice

5 minutes

In this exercise, you create a microservice endpoint and containerize it by using the .NET SDK and Docker.

Note

You can complete this exercise in an instance of GitHub Codespaces that has Docker and the .NET SDK preinstalled. When you use these tools and techniques in your own development environment, make sure that you have these prerequisites installed.

Open the development environment

You can choose to use a GitHub codespace that hosts the exercise, or complete the exercise locally in Visual Studio Code.

To use a codespace, create a preconfigured GitHub Codespace with this Codespace creation link.

GitHub takes several minutes to create and configure the codespace. When the process completes, you see the code files for the exercise. The code used for the remainder of this module is in the /dotnet-docker directory.

To use Visual Studio Code, clone the https://github.com/MicrosoftDocs/mslearn-dotnet-cloudnative repository to your local machine. Then:

Install any system requirements to run Dev Container in Visual Studio Code.
Make sure Docker is running.
In a new Visual Studio Code window open the folder of the cloned repository
Press Ctrl+Shift+P to open the command palette.
Search: >Dev Containers: Rebuild and Reopen in Container
Select eShopLite - dotnet-docker from the drop-down. Visual Studio Code creates your development container locally.

Use .NET publish to create the Products back-end image

The latest .NET 8 release improves support for containerization. You can use the dotnet publish command to create a Docker image for your microservices. The command creates a rootless container image that runs services under an app account. Running rootless containers is great for security and performance. The command knows how to pick the best base image by checking the settings in the project file.

To create the images for all the eShopLite services, go to the TERMINAL tab and run this command:

cd ./dotnet-docker 
 dotnet publish /p:PublishProfile=DefaultContainer

You see output like the following messages:

DataEntities -> /workspaces/mslearn-dotnet-cloudnative/dotnet-docker/DataEntities/bin/Release/net8.0/publish/
Products -> /workspaces/mslearn-dotnet-cloudnative/dotnet-docker/Products/bin/Release/net8.0/Products.dll
Products -> /workspaces/mslearn-dotnet-cloudnative/dotnet-docker/Products/bin/Release/net8.0/publish/
Store -> /workspaces/mslearn-dotnet-cloudnative/dotnet-docker/Store/bin/Release/net8.0/Store.dll
Store -> /workspaces/mslearn-dotnet-cloudnative/dotnet-docker/Store/bin/Release/net8.0/publish/
Building image 'store' with tags 'latest' on top of base image 'mcr.microsoft.com/dotnet/aspnet:8.0'.
Building image 'products' with tags 'latest' on top of base image 'mcr.microsoft.com/dotnet/aspnet:8.0'.
Pushed image 'store:latest' to local registry via 'docker'.
Pushed image 'products:latest' to local registry via 'docker'.

The command reads the solution file, determined it contains three projects, built them, and created images for the store and products projects. The images are named after the projects and published into the local docker registry.

Check the images are available in docker:

docker images

You see output like the following messages:

REPOSITORY                          TAG       IMAGE ID       CREATED              SIZE
products                            latest    63614e340088   About a minute ago   293MB
store                               latest    e9458c3abdb1   About a minute ago   218MB

Use a Dockerfile to create the Products back-end image

If you want more control of how the images are built, you can use a Dockerfile to create an image for the Products web service.

In the EXPLORER pane, create a file named Dockerfile in ./dotnet-docker/Products. The file is empty.
Enter the following code:
```
FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build

WORKDIR /DataEntities
COPY "DataEntities/DataEntities.csproj" .
RUN dotnet restore
COPY "DataEntities" .
RUN dotnet publish -c release -o /app
```
After completing the following steps, this code will set up the DataEntities library in the Products docker image:
- Pull the mcr.microsoft.com/dotnet/sdk:8.0 image and name the image build.
- Set the working directory within the image to /DataEntities.
- Copy the file named DataEntities.csproj found locally to the /DataEntities directory that you created.
- Call dotnet restore on the project.
- Copy everything in the local DataEntities directory to the image.
- Call dotnet publish on the project.
Directly below the last line, enter this code:
```
 WORKDIR /src
 COPY Products/Products.csproj .
 RUN dotnet restore
 COPY Products .
 RUN dotnet publish -c release -o /app
```
This code does the following steps sequentially when invoked:
- Set the working directory within the image to /src.
- Copy the file named Products.csproj found locally to the /src directory that you created.
- Call dotnet restore on the project.
- Copy everything in the local Products directory to the image.
- Call dotnet publish on the project.
Directly below the last line, enter this code:
```
 FROM mcr.microsoft.com/dotnet/aspnet:8.0
 WORKDIR /app
 EXPOSE 80
 EXPOSE 443
 COPY --from=build /app .
 ENTRYPOINT ["dotnet", "Products.dll"]
```
This code does the following steps sequentially when invoked:
- Pull the mcr.microsoft.com/dotnet/aspnet:8.0 image.
- Set the working directory within the image to /app.
- Expose port 80 and 443.
- Copy everything from the app directory of the build image you created into the app directory of this image.
- Set the entry point of this image to dotnet and pass Products.dll as an argument.

Create the Docker image

Having completed the Dockerfile, the next step is to use it to create a Docker image:

To create the image for the Products back-end service, go to the TERMINAL tab and run this command:
```
cd ./dotnet-docker 
 docker build -t productsbackend:latest -f Products/Dockerfile .
```
This runs the commands in Dockerfile in the current directory and applies the tag productsbackend:latest to the resulting image.

After much output, the image will be built. Entering docker images shows you a list of all images in your codespace including productsbackend. The other image is the one for the codespace itself.

You see output like the following messages:

REPOSITORY                          TAG       IMAGE ID       CREATED              SIZE
products                            latest    63614e340088   10 minutes ago       293MB
store                               latest    e9458c3abdb1   10 minutes ago       218MB
productsbackend                     latest   190783f7e06f    About a minute ago   293MB

Think about the difference between using dotnet publish and having to manually create the Dockerfiles for each microservice in your apps.

Run the container and test the service

Now you can use the image to run and host the Products service.

To create and run a container from the new products image and expose the service on port 32001, run this command:
```
docker run -it --rm -p 32001:8080  products
```
Or if you'd like to run the image you created using the Dockerfile, run:
```
docker run -it --rm -p 32001:8080 productsbackend
```
To test the service, switch to the PORTS tab then, to the right of the local address for the Back End port, select the globe icon. The browser opens a new tab at that address.

To query some products, append the address with /api/product and then press Enter. You should see some product information listed in JSON format.

[
    {
        "id": 1,
        "name": "Solar Powered Flashlight",
        "description": "A fantastic product for outdoor enthusiasts",
        "price": 19.99,
        "imageUrl": "product1.png"
    },
    {
        "id": 2,
        "name": "Hiking Poles",
        "description": "Ideal for camping and hiking trips",
        "price": 24.99,
        "imageUrl": "product2.png"
    },
    {
        "id": 3,
        "name": "Outdoor Rain Jacket",
        "description": "This product will keep you warm and dry in all weathers",
        "price": 49.99,
        "imageUrl": "product3.png"
    },
    ...
]

Exercise - Build a container image for your .NET microservice

Open the development environment

Use .NET publish to create the Products back-end image

Use a Dockerfile to create the Products back-end image

Create the Docker image

Run the container and test the service

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