Third stop on the Docker learning train - Quickstart: Compose and ASP.NET Core with SQL Server

The third stop on my Docker learning train is a recommendation from the Docker Samples. The tutorial is titled 'Quickstart: Compose and ASP.NET Core with SQL Server'. This is going to be a whistle-stop.

This tutorial shows using the Docker Engine running on Linux to set up and run an ASP.NET Core application using a .NET Cor SKD image and SQL Server on Linux image. The tutorial makes use of Docker Compose for defining and running multiple container applications.

The tutorial references an older version (2.1) of the .NET Core libraries. My computer is running a newer (3.1) version of the .NET Core libraries. I wanted to see what error messages and problems running this setup would be.

The first change I made was to the docker-compose.yml file. I changed the port from 8000 to 9090 because I already had a different container using port 8000 and 9000. The second change made was in the "startup.cs" file. I commented out the setting up the connection variable. I moved the value of the connection to the "DefaultConnection" in the "appsettings.json" file. I needed to make a few more changes to the rest of the "ConfigureServices" method.

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;";

    services.Configure (options => {
    // This lambda determines whether user consent for non-essential cookies is needed for a given request.
        options.CheckConsentNeeded = context => true;
        options.MinimumSameSitePolicy = SameSiteMode.None;
        });

    services.AddDbContext (options =>
        options.UseSqlServer (
            Configuration.GetConnectionString ("DefaultConnection")));
    services.AddDefaultIdentity ()
        .AddEntityFrameworkStores ();

    services.AddMvc ().SetCompatibilityVersion (CompatibilityVersion.Version_2_1);
}

On my computer, I encountered an issue with running 'docker-compose build'. The error message was

"ERROR: Couldn't connect to Docker daemon at http+docker://localhost - is it running?
If it's at a non-standard location, specify the URL with the DOCKER_HOST environment variable."

After a bit of research, I came to find out that this is a fairly generic and common message that could have several possible causes. For me, it turned out the I needed to change the permissions on the "docker.sock" file. I fixed the issue be running

sudo chmod 666 /var/run/docker.sock

The running of the command 'docker-compose up' wrote many messages to the console that gives the appearance of that the application and database are running. I can also have a couple of active containers. When I navigate to localhost:9090, the browser displays a "This site can't be reached" message. I am not going to take the time to figure out the problem at this time.

References 

Docker Compose - "Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration."

The article on Medium "If you faced an issue like 'Couldn't connect to Docker daemon at http+docker://localunixsocket -- is it running?'..." was helpful in dealing with an error from running 'docker-compose build'