docker container exits immediately even with Conso

Question

I am trying to run a .net core 1.0.0 console application inside a docker container.
When I run dotnet run command from inside the Demo folder on my machine, it works fine; But when run using docker run -d --name demo Demo, the container exits immediately.

I tried docker logs demo to check the logs and it just shows the text from the Console.WriteLine:

Demo app running...

and nothing else.

I have uploaded the project at https://github.com/learningdockerandnetcore/Demo

The project contains Programs.cs, Dockerfile used to create Demo image, and project.json file.

Answer 1

You can use:

Thread.Sleep(Timeout.Infinite);

See this answer:

Is Thread.Sleep(Timeout.Infinite); more efficient than while(true){}?

Answer 2

The only way I could get Docker/Linux to keep my .NET Core application alive was to spoof ASP.NET into hosting it for me... This is such an ugly hack!!

Doing it this way will run in Docker using the docker run -d option, so you don't have to have a live connection to keep the STDIN stream alive.

I Created a .NET Core console application (not an ASP.NET app) and my Program class looks like this:

public class Program
{
    public static ManualResetEventSlim Done = new ManualResetEventSlim(false);
    public static void Main(string[] args)
    {
        //This is unbelievably complex because .NET Core Console.ReadLine() does not block in a docker container...!
        var host = new WebHostBuilder().UseStartup(typeof(Startup)).Build();

        using (CancellationTokenSource cts = new CancellationTokenSource())
        {
            Action shutdown = () =>
            {
                if (!cts.IsCancellationRequested)
                {
                    Console.WriteLine("Application is shutting down...");
                    cts.Cancel();
                }

                Done.Wait();
            };

            Console.CancelKeyPress += (sender, eventArgs) =>
            {
                shutdown();
                // Don't terminate the process immediately, wait for the Main thread to exit gracefully.
                eventArgs.Cancel = true;
            };

            host.Run(cts.Token);
            Done.Set();
        }
    }      
}

The Startup class:

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<IServer, ConsoleAppRunner>();
    }


    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
    }
}

The ConsoleAppRunner class

public class ConsoleAppRunner : IServer
{

    /// <summary>A collection of HTTP features of the server.</summary>
    public IFeatureCollection Features { get; }

    public ConsoleAppRunner(ILoggerFactory loggerFactory)
    {
        Features = new FeatureCollection();
    }

    /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
    public void Dispose()
    {

    }

    /// <summary>Start the server with an application.</summary>
    /// <param name="application">An instance of <see cref="T:Microsoft.AspNetCore.Hosting.Server.IHttpApplication`1" />.</param>
    /// <typeparam name="TContext">The context associated with the application.</typeparam>
    public void Start<TContext>(IHttpApplication<TContext> application)
    {
        //Actual program code starts here...
        Console.WriteLine("Demo app running...");

        Program.Done.Wait();        // <-- Keeps the program running - The Done property is a ManualResetEventSlim instance which gets set if someone terminates the program.

    }
}

The only nice thing about it is that you get to use DI in your application (if you want to) - so in my use case, I am using the ILoggingFactory to handle my logging.

Edit 30th Oct 2018 This post still seems to be popular - I'd like to just point out to anyone reading my old post that it is now pretty ancient. I was basing it on .NET core 1.1 (which was new at the time). It is likely that if you are using a newer version of.NET core (2.0 / 2.1 or greater) that there is probably a much better way of solving this problem now. Please take time to look at some of the other posts on this thread which may not be as highly ranked as this one, but may be newer and more up-to-date.

Answer 3

Using Console.ReadLine instead seems to work.

C#:

do
{
    Console.WriteLine($"Type: quit<Enter> to end {Process.GetCurrentProcess().ProcessName}");
}
while (!Console.ReadLine().Trim().Equals("quit",StringComparison.OrdinalIgnoreCase));

F#:

while not (Console.ReadLine().Trim().Equals("quit",StringComparison.OrdinalIgnoreCase)) do
    printfn "Type: quit<Enter> to end"

Answer 4

one more "dirty way" is to start your program in screen using

screen -dmS yourprogramm

Answer 5

I am not sure why Console.ReadLine(); doesn't block the main thread when running a dotnet core console app in a detached docker container, but the best solution is to register a ConsoleCancelEventHandler with the Console.CancelKeyPress event.

Then you can instead block the main thread with a type of Threading WaitHandle and signal the release of the main thread when Console.CancelKeyPress is fired.

A good example code can be found here: https://gist.github.com/kuznero/73acdadd8328383ea7d5

Answer 6

If you switch your app to target .net core 2.0, then you can use Microsoft.Extensions.Hosting pacakge to host a .net core console application by using the HostBuilder API to start/stop your application. Its ConsoleLifetime class would process the general aplication start/stop method.

In order to run your app, you should implement your own IHostedService interface or inherit from the BackgroundService class, then add it to host context within ConfigureServices.

namespace Microsoft.Extensions.Hosting
{
    //
    // Summary:
    //     Defines methods for objects that are managed by the host.
    public interface IHostedService
    {
        // Summary:
        // Triggered when the application host is ready to start the service.
        Task StartAsync(CancellationToken cancellationToken);

        // Summary:
        // Triggered when the application host is performing a graceful shutdown.
        Task StopAsync(CancellationToken cancellationToken);
    }
}

Here's a sample hosted service:

public class TimedHostedService : IHostedService, IDisposable
{
    private readonly ILogger _logger;
    private Timer _timer;

    public TimedHostedService(ILogger<TimedHostedService> logger)
    {
        _logger = logger;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Timed Background Service is starting.");

        _timer = new Timer(DoWork, null, TimeSpan.Zero, 
            TimeSpan.FromSeconds(5));

        return Task.CompletedTask;
    }

    private void DoWork(object state)
    {
        _logger.LogInformation("Timed Background Service is working.");
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Timed Background Service is stopping.");

        _timer?.Change(Timeout.Infinite, 0);

        return Task.CompletedTask;
    }

    public void Dispose()
    {
        _timer?.Dispose();
    }
}

Then creating the HostBuilder and adding the service and other componments (logging, configuration).

public class Program
{
    public static async Task Main(string[] args)
    {
        var hostBuilder = new HostBuilder()
             // Add configuration, logging, ...
            .ConfigureServices((hostContext, services) =>
            {
                // Add your services with depedency injection.
            });

        await hostBuilder.RunConsoleAsync();
    }
}