Docker: Cannot launch ASP.Net Core 5 Web Api on browser after docker run

Question

I decided it was time for learning docker and for this I have an asp.net core api project that runs perfectly on IIS express. This project is a simple REST API. The goal here is to set a basic get entry point, check if it works on IIS Express and then create a Dockerfile in order to deploy my app. I post the question because I tried to find out response on web and stackoverflow.

For this I already have a basic startup class:

namespace app.rest
{
    public class Startup
    {
        private readonly string ConnectionString;
        public IConfiguration Configuration { get; }

        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
        public void ConfigureServices(IServiceCollection services)
        {    
            services.AddScoped<AppService, AppServiceImpl>();
            services.AddScoped<ApiEntryPointService, ApiEntryPointServiceImpl>();    
            services.AddControllers();
            services.AddSwaggerGen(c =>
            {
                c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebApplication", Version = "v1" });
            });
            services.AddMvc();
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseSwagger();
                app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebApplication v1"));
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();
            }
            // app.UseHttpsRedirection();
            app.UseRouting();
            app.UseAuthorization();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }    
    }
}

A Program class that have been automatically implemented on project creation.

namespace app.rest
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

And a simple controller :

namespace app.rest.Controllers
{

    [Route("api/[controller]")]
    [ApiController]
    public class AppController
    {
          
        // GET api/<AppController>/5
        [HttpGet]
        public string Get()
        {
            return "Hello World";
        }
    }
}

this works fine when I use IIS Express and I can see my hello world. My dockerfile can build the image and i can even run it.

Here is my Dockerfile :

FROM mcr.microsoft.com/dotnet/sdk:5.0 AS base
WORKDIR /appSource
EXPOSE 5000

FROM mcr.microsoft.com/dotnet/sdk:5.0 AS build
WORKDIR /appBuild
# Copy csproj and restore as distinct layers
COPY *.sln .
COPY *.csproj .

#RUN mkdir /tmp/build/
#COPY . /tmp/build
#RUN find /tmp/build -name *.csproj

RUN dotnet restore app.rest.csproj --verbosity detailed
# Copy everything else and build
COPY . .
WORKDIR /appBuild/app.rest
RUN dotnet build "../app.rest.csproj" -c Release -o /appSource --no-restore

FROM build AS publish
WORKDIR /appBuild/app.rest
RUN dotnet publish "../app.rest.csproj" -c Release -o /appSource


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

TO build the image I simply type :

 docker build --pull -t app.rest .

And as I expose the port 5000, I launch a docker run command and bind ports (if i understood correctly what i'm doing):

docker run -d -p 5000:5000 -it app.rest

I checked logs and there's no particular issues:

warn: Microsoft.AspNetCore.DataProtection.Repositories.FileSystemXmlRepository[60]
Storing keys in a directory 'C:\Users\ContainerUser\AppData\Local\ASP.NET\DataProtection-Keys' that may not be persisted outside of the c]0;C:\Program Files\dotnet\dotnet.exeontainer. Protected data will be unavailable when container is destroyed.
info: Microsoft.Hosting.Lifetime[0]
Now listening on: http://localhost:5000
info: Microsoft.Hosting.Lifetime[0]
Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
Hosting environment: Production
info: Microsoft.Hosting.Lifetime[0]
Content root path: C:\appSource

I should be able to connect to this api with this URL: http://localhost:5000/api/App Unfortunatelly it's not the case.

Answer 1

Your run-time docker image is the sdk one. Usually the sdk image is only used for building the artefacts (i.e. compilation and publishing). Instead, try using the Microsoft run-time image equivalent mcr.microsoft.com/dotnet/aspnet:5.0.

So,

...
FROM mcr.microsoft.com/dotnet/aspnet:5.0 AS base
...
FROM base AS final
WORKDIR /appSource
COPY --from=publish /appSource .
EXPOSE 5000
ENTRYPOINT ["dotnet", "app.rest.dll"]

This might fix your problem. When I tried to run one of my own from the sdk image it wouldn't respond to http requests.

Answer 2

Here is the solution I finally implemented and which works:

FROM mcr.microsoft.com/dotnet/sdk:5.0 AS build
WORKDIR /source

# copy csproj and restore as distinct layers
COPY *.sln .
COPY *.csproj ./
RUN dotnet restore

# copy everything else and build app
COPY /. ./
WORKDIR /source
RUN dotnet publish -c release -o /app --no-restore

# final stage/image
FROM mcr.microsoft.com/dotnet/aspnet:5.0
WORKDIR /app
COPY --from=build /app ./
ENTRYPOINT ["dotnet", "app.rest.dll"]

Solving issue at 3 in the morning helps to find solutions... Here comes the inspiration.

https://github.com/dotnet/dotnet-docker/tree/main/samples/aspnetapp