Multistage builds in Docker and dotnetcore

Introduction: Docker has revolutionized the world of application deployment with its lightweight and portable containerization solution. In this comprehensive blog post, we will delve into the process of running a .NET Core application using Docker’s powerful multistage build feature. Additionally, we will leverage Mermaid diagrams to visually illustrate the containerization process and a sequence diagram to provide a clear understanding of the multistage build steps.

Prerequisites:

Before we begin, ensure you have the following software installed on your system:

1. Docker Desktop (Download from https://www.docker.com/products/docker-desktop)
2. .NET SDK (Download from https://dotnet.microsoft.com/download)

Step 1: Create a .NET Core Application We will start by creating a simple .NET Core application. Open your terminal or command prompt and execute the following command to create a new console application:

dotnet new console -n MyDotNetApp

Step 2: Implement the .NET Core Application Open the MyDotNetApp/Program.cs file and add the following code to the Main method:

using System;

namespace MyDotNetApp
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("Hello, Docker!");
        }
    }
}

*Step 3: Create the Dockerfile Next, create a Dockerfile in the root of your project to define the Docker image build process:

Stage 1: Build the .NET Core application

FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /app

COPY . .
RUN dotnet publish -c Release -o out

Stage 2: Create a runtime image

FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app
COPY --from=build /app/out .

Set the entry point for the application

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

Step 4: Build the Docker Image In your terminal or command prompt, navigate to the root of your project where the Dockerfile is located. Build the Docker image using the following command:

docker build -t my-dotnet-app .

Step 5: Run the Docker Container Once the Docker image is built, run a container with the following command:

docker run --rm my-dotnet-app` 

Step 6: Verify the Output If everything is set up correctly, you should see the “Hello, Docker!” message printed in the terminal.

Understanding the Multistage Build Process with a Sequence Diagram

To gain a deeper understanding of the Docker multistage build process, let’s create a sequence diagram:

# Stage 1: Build the .NET Core application
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /app

COPY . .
RUN dotnet publish -c Release -o out

# Stage 2: Create a runtime image
FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app
COPY --from=build /app/out .

# Set the entry point for the application
ENTRYPOINT ["dotnet", "MyDotNetApp.dll"]

Conclusion:

In this comprehensive blog post, we explored the process of running a .NET Core application using Docker’s multistage build feature. By leveraging Docker’s containerization, we effortlessly packaged our application along with its dependencies, ensuring consistent deployment across various environments. The multistage build effectively reduced Docker image size, enhancing efficiency and expediting deployment.