Containerizing C# Applications with Docker: A Step-by-Step Guide

Why does your C# project need Docker?

Imagine this scenario: you wrote a cool C# application on your Windows 11 laptop, installed all the libraries, configured the database, and it works perfectly. But when you hand the project over to a colleague on macOS or upload it to a Linux server, the nightmare begins: "I have a different version of .NET", "where is SQL Server?", "you hardcoded the file paths in the code"... Sound familiar?

This is exactly where containerizing C# applications with Docker comes to the rescue. Docker allows you to package your application together with all its dependencies, settings, and even the operating system into a lightweight container. And it will work identically everywhere: on your PC, on your colleague's server, in the AWS or Azure cloud.

In this article, we will break down how to containerize C# applications with Docker from A to Z. You will learn how to create a Dockerfile for ASP.NET Core, how to optimize the image size, and how to run it all with a single command. Let's go!

What is Docker and why does a C# developer need it?

Docker is a platform for containerizing applications. A container is an isolated environment that contains your application and everything it needs to run: runtime, libraries, environment variables, configs. Unlike virtual machines, containers share the host OS kernel, so they start faster and take up less space.

For a .NET developer, Docker offers several killer features:

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• Eliminates the "it works on my machine" problem — the container guarantees a consistent environment
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• Simplifies CI/CD — you build the image once and use it everywhere
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• Microservice architecture — each C# service lives in its own container
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• Scalability — easily launch 10 copies of your API in seconds
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• Isolation — dependencies of one project do not conflict with another
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If you are not yet using .NET application containerization, now is the perfect time to start. And we will do it right now.

Preparation: what you need to install

Before starting containerizing C#, make sure you have installed:

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1. Docker Desktop — download from the official website. For Windows, be sure to enable WSL 2 (hints will be provided during installation).
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2. .NET SDK 8.0 (or 7.0/9.0 — it doesn't matter) — download from Microsoft.
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3. VS Code or Visual Studio 2022 — for convenient code editing.
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Verify the installation with these terminal commands:

docker --version\ndotnet --version

If both commands return a version number — you are all set for Docker development for .NET.

Creating a simple C# application for containerization

For demonstration, let's take a minimal ASP.NET Core Web API. Create a project in an empty folder:

dotnet new webapi -n MyDockerApp\ncd MyDockerApp

Open the Program.cs file and simplify it to look like this (for clarity):

var builder = WebApplication.CreateBuilder(args);\nvar app = builder.Build();\n\napp.MapGet("/", () => "Hello from Dockerized C# App!");\n\napp.Run();

Run it locally to make sure everything works:

dotnet run

Navigate in your browser to http://localhost:5000 (or the port the console shows). See the greeting? Great. Now let's package this application into Docker.

Writing a Dockerfile for a C# application

Dockerfile is the instruction for building an image. For <