How to containerize a .NET and SQL Server app

Terry Mace | November 3

In the video above, walk you through how to containerize a .NET app and SQL Server database using Docker – from start to finish.

We cover Dockerfiles, Docker Compose, Docker Hub, and the core containerization concepts that every .NET developer should understand.

In this tutorial, you’ll learn:

What Docker, Containers, Images, and Dockerfiles actually are
Why containers make .NET development faster and more consistent
How to build and run your own .NET container image
How to connect it to a SQL Server container
How to use Docker Compose to run them both with a single command
How to persist your SQL data using volumes
How to keep your passwords secure with environment variables

By the end, you’ll have a fully containerized .NET app that runs identically on any machine – Windows, macOS, or Linux.

Dockerfile

Below is the Dockerfile created in the video.
This file defines each step required to build, publish, and run your .NET app inside a container.
It uses a multi-stage build to keep the final image small, clean, and production-ready.

FROM mcr.microsoft.com/dotnet/aspnet:9.0 AS base
USER $APP_UID
WORKDIR /app
EXPOSE 8080
EXPOSE 8081

FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
ARG BUILD_CONFIGURATION=Release
WORKDIR /src
COPY ["BookMvcApp.csproj", "./"]
RUN dotnet restore "BookMvcApp.csproj"
COPY . .
RUN dotnet build "./BookMvcApp.csproj" -c $BUILD_CONFIGURATION -o /app/build

FROM build AS publish
ARG BUILD_CONFIGURATION=Release
RUN dotnet publish "./BookMvcApp.csproj" -c $BUILD_CONFIGURATION -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "BookMvcApp.dll"]

FROM mcr.microsoft.com/dotnet/aspnet:9.0 AS base
USER $APP_UID
WORKDIR /app
EXPOSE 8080
EXPOSE 8081

FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
ARG BUILD_CONFIGURATION=Release
WORKDIR /src
COPY ["BookMvcApp.csproj", "./"]
RUN dotnet restore "BookMvcApp.csproj"
COPY . .
RUN dotnet build "./BookMvcApp.csproj" -c $BUILD_CONFIGURATION -o /app/build

FROM build AS publish
ARG BUILD_CONFIGURATION=Release
RUN dotnet publish "./BookMvcApp.csproj" -c $BUILD_CONFIGURATION -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "BookMvcApp.dll"]

How it works

Base stage – Defines the runtime environment (ASP.NET 9 image).
Build stage – Uses the SDK to compile the app and restore dependencies.
Publish stage – Packages the app into a ready-to-run format.
Final stage – Produces the minimal runtime image with only published output.

This pattern ensures smaller, faster, and more secure images.

Docker Compose File

Next, we create a docker-compose.yml file to run both the web app and SQL Server containers together.

version: '3.9'

services:
  web:
    build: .
    ports:
      - "8080:8080"
    depends_on:
      - db
    environment:
      - ConnectionStrings__DefaultConnection=Server=db;Database=BookDb;User Id=sa;Password=${DB_PASSWORD};TrustServerCertificate=True;
  db:
    image: mcr.microsoft.com/mssql/server:2022-latest
    environment:
      - ACCEPT_EULA=Y
      - SA_PASSWORD=${DB_PASSWORD}
    ports:
      - "1433:1433"
    volumes:
      - mssql-data:/var/opt/mssql
  
volumes:
  mssql-data:

version: '3.9'

services:
  web:
    build: .
    ports:
      - "8080:8080"
    depends_on:
      - db
    environment:
      - ConnectionStrings__DefaultConnection=Server=db;Database=BookDb;User Id=sa;Password=${DB_PASSWORD};TrustServerCertificate=True;
  db:
    image: mcr.microsoft.com/mssql/server:2022-latest
    environment:
      - ACCEPT_EULA=Y
      - SA_PASSWORD=${DB_PASSWORD}
    ports:
      - "1433:1433"
    volumes:
      - mssql-data:/var/opt/mssql
  
volumes:
  mssql-data:

Key points

The web service builds your .NET app using the Dockerfile.
The db service pulls Microsoft’s official SQL Server 2022 image from Docker Hub.
${DB_PASSWORD} is read from your local .env file, keeping credentials out of version control.
The named volume mssql-data persists your database data even after containers are stopped.

With this setup, you can spin up both containers – app and database – in one command:

docker compose up --build

docker compose up --build

Final Thoughts

This simple setup gives you a portable, reproducible, and production-ready development environment for any .NET application.

You can now:

Onboard new developers in minutes
Run your app identically across all machines
Prepare for easy cloud deployments

Mace Labs