Quickstart: Compose and ASP.NET Core with SQL Server

Estimated reading time: 6 minutes

This quick-start guide demonstrates how to use Docker Engine on Linux and Docker Compose to set up and run the sample ASP.NET Core application using the .NET Core SDK image with the SQL Server on Linux image. You just need to have Docker Engine and Docker Compose installed on your platform of choice: Linux, Mac or Windows.

For this sample, we create a sample .NET Core Web Application using the microsoft/dotnet:2.1-sdk Docker image. After that, we create a Dockerfile, configure this app to use our SQL Server database, and then create a docker-compose.yml that defines the behavior of all of these components.

Note: This sample is made for Docker Engine on Linux. For Windows Containers, visit Docker Labs for Windows Containers.

Create a new directory for your application.

This directory is the context of your docker-compose project. For Docker Desktop for Windows and Docker Desktop for Mac, you need to set up file sharing for the volume that you need to map.
Within your directory, use the dotnet:2.1-sdk Docker image to generate a sample web application within the container under the /app directory and into your host machine in the working directory:
```
$ docker run -v ${PWD}:/app --workdir /app microsoft/dotnet:2.1-sdk dotnet new mvc --auth Individual
```
Note: If running in Docker Desktop for Windows, make sure to use Powershell or specify the absolute path of your app directory.
Create a Dockerfile within your app directory and add the following content:
```
FROM microsoft/dotnet:2.1-sdk
COPY . /app
WORKDIR /app
RUN ["dotnet", "restore"]
RUN ["dotnet", "build"]
EXPOSE 80/tcp
RUN chmod +x ./entrypoint.sh
CMD /bin/bash ./entrypoint.sh
```
This file defines how to build the web app image. It uses the .NET Core SDK image, maps the volume with the generated code, restores the dependencies, builds the project and exposes port 80. After that, it calls an entrypoint script that we create in the next step.
The Dockerfile makes use of an entrypoint to your webapp Docker image. Create this script in a file called entrypoint.sh and paste the contents below.

Note: Make sure to use UNIX line delimiters. The script doesn’t work if you use Windows-based delimiters (Carriage return and line feed).
```
#!/bin/bash

set -e
run_cmd="dotnet run --server.urls http://*:80"

until dotnet ef database update; do
>&2 echo "SQL Server is starting up"
sleep 1
done

>&2 echo "SQL Server is up - executing command"
exec $run_cmd
```
This script restores the database after it starts up, and then runs the application. This allows some time for the SQL Server database image to start up.
Create a docker-compose.yml file. Write the following in the file, and make sure to replace the password in the SA_PASSWORD environment variable under db below. This file defines the way the images interact as independent services.

Note: The SQL Server container requires a secure password to startup: Minimum length 8 characters, including uppercase and lowercase letters, base 10 digits and/or non-alphanumeric symbols.
```
version: "3.9"
services:
    web:
        build: .
        ports:
            - "8000:80"
        depends_on:
            - db
    db:
        image: "mcr.microsoft.com/mssql/server"
        environment:
            SA_PASSWORD: "Your_password123"
            ACCEPT_EULA: "Y"
```
This file defines the web and db micro-services, their relationship, the ports they are using, and their specific environment variables.

Note: You may receive an error if you choose the wrong Compose file version. Be sure to choose a version that is compatible with your system.

Go to Startup.cs and locate the function called ConfigureServices (Hint: it should be under line 42). Replace the entire function to use the following code (watch out for the brackets!).

Note: Make sure to update the Password field in the connection variable below to the one you defined in the docker-compose.yml file.

[...]
public void ConfigureServices(IServiceCollection services)
{
    // Database connection string.
    // Make sure to update the Password value below from "Your_password123" to your actual password.
    var connection = @"Server=db;Database=master;User=sa;Password=Your_password123;";

    // This line uses 'UseSqlServer' in the 'options' parameter
    // with the connection string defined above.
    services.AddDbContext<ApplicationDbContext>(
        options => options.UseSqlServer(connection));

    services.AddIdentity<ApplicationUser, IdentityRole>()
        .AddEntityFrameworkStores<ApplicationDbContext>()
        .AddDefaultTokenProviders();

    services.AddMvc();

    // Add application services.
    services.AddTransient<IEmailSender, AuthMessageSender>();
    services.AddTransient<ISmsSender, AuthMessageSender>();
}
[...]

Go to app.csproj. You see a line like:
```
<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="1.1.2" />
```
The generated project uses sqlite by default. To use SQL Server, add this line to app.csproj:
```
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="1.1.2" />
```
The Sqlite dependency was at version 1.1.2 at the time of this writing. Use the same version for the SQL Server dependency.
Ready! You can now run the docker-compose build command.
```
$ docker-compose build
```
Make sure you allocate at least 2GB of memory to Docker Engine. Here is how to do it on Docker Desktop for Mac and Docker Desktop for Windows. This is necessary to run the SQL Server on Linux container.
Run the docker-compose up command. After a few seconds, you should be able to open localhost:8000 and see the ASP.NET core sample website. The application is listening on port 80 by default, but we mapped it to port 8000 in the docker-compose.yml.
```
$ docker-compose up
```
Go ahead and try out the website! This sample uses the SQL Server database image in the back-end for authentication.

Ready! You now have an ASP.NET Core application running against SQL Server in Docker Compose! This sample made use of some of the most popular Microsoft products for Linux. To learn more about Windows Containers, check out Docker Labs for Windows Containers to try out .NET Framework and more SQL Server tutorials.

Next steps

dotnet, .NET, Core, example, ASP.NET Core, SQL Server, mssql