.NET Containerization with Docker: A Complete Guide

By Sandeep Mhaske | Feb 2025

Table of Contents

1. Introduction
2. Why Containerization for .NET Applications?
3. Docker Basics
4. Creating a Dockerfile for a .NET Application
5. Using Docker Compose for .NET Applications
6. Best Practices for Containerizing .NET Applications
7. Tutorial: Containerizing an ASP.NET Core App
8. Conclusion

Introduction

In the era of cloud-native development, containerization has become a key practice for deploying scalable and portable applications. Docker, the leading containerization platform, makes it possible to package .NET applications with all their dependencies into containers, ensuring consistency across environments.

This guide explores how to containerize .NET applications using Docker, covering its benefits, practical implementation, and best practices.

Why Containerization for .NET Applications?

Containerizing .NET applications offers several advantages:

• Environment Consistency: Containers eliminate the "it works on my machine" problem by providing a consistent runtime environment.
• Scalability: Containers can be scaled horizontally across multiple nodes with orchestration tools like Kubernetes.
• Portability: Containers can run on any platform supporting Docker, from local machines to cloud providers.
• Efficient Resource Utilization: Containers use fewer resources than virtual machines.
• Rapid Deployment: Build, test, and deploy containers quickly using CI/CD pipelines.

Docker Basics

Docker is an open-source platform for developing, shipping, and running applications in containers. It uses lightweight, standalone, and executable packages known as containers that include everything needed to run the software.

Core Docker Components

• Docker Engine: The runtime for creating and managing containers.
• Docker Image: A read-only template used to create containers.
• Docker Container: A running instance of a Docker image.
• Dockerfile: A script to automate the creation of Docker images.
• Docker Compose: A tool for defining and running multi-container applications.

Creating a Dockerfile for a .NET Application

A Dockerfile is a script that contains a series of commands to build a Docker image for your application. Here's an example for an ASP.NET Core application:

# Use the official .NET runtime image as a base
FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
WORKDIR /app
EXPOSE 80

# Use the official .NET SDK image for build
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["MyApp/MyApp.csproj", "MyApp/"]
RUN dotnet restore "MyApp/MyApp.csproj"
COPY . .
WORKDIR "/src/MyApp"
RUN dotnet build "MyApp.csproj" -c Release -o /app/build

# Publish the application
FROM build AS publish
RUN dotnet publish "MyApp.csproj" -c Release -o /app/publish

# Build the runtime image
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "MyApp.dll"]
            

Save this file as Dockerfile in your project directory.

Using Docker Compose for .NET Applications

Docker Compose simplifies running multi-container applications. Here's an example docker-compose.yml for an ASP.NET Core application with a SQL Server database:

version: '3.4'

services:
  webapp:
    image: myapp:latest
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "5000:80"
    depends_on:
      - db

  db:
    image: mcr.microsoft.com/mssql/server:2019-latest
    environment:
      SA_PASSWORD: "YourPassword123"
      ACCEPT_EULA: "Y"
    ports:
      - "1433:1433"
            

Run docker-compose up to start the application.

Best Practices for Containerizing .NET Applications

• Use multi-stage builds to reduce image size.
• Keep the Dockerfile clean and minimal.
• Use environment variables for sensitive data.
• Regularly scan Docker images for vulnerabilities.
• Optimize layers in the Dockerfile for better caching.

Tutorial: Containerizing an ASP.NET Core App

Step 1: Create a Dockerfile

Follow the Dockerfile example provided above.

Step 2: Build the Docker Image

Run the following command:

docker build -t myapp .

Step 3: Run the Container

Start the container using:

docker run -d -p 5000:80 myapp

Step 4: Access the Application

Visit http://localhost:5000 in your browser.

Conclusion

Docker revolutionizes the way .NET applications are developed and deployed by offering portability, scalability, and consistency. By following the steps outlined in this guide, you can effectively containerize your .NET applications and leverage the power of containerization in modern software development.