[SOLVED] ASP.NET Core on docker returns ERR_EMPTY_RESPONSE when browsing at localhost

Issue

When I try to run my ASP.NET Core application on docker through http://localhost:5004 I’m getting this response from my browser: ERR_CONNECTION_REFUSED

Here’s my docker file

# https://hub.docker.com/_/microsoft-dotnet
FROM mcr.microsoft.com/dotnet/sdk:5.0.404 AS build


WORKDIR /code

COPY . .

# copy everything else and build app

RUN dotnet publish -c release -o /app 

# final stage/image
FROM mcr.microsoft.com/dotnet/aspnet:5.0.13

WORKDIR /app
COPY --from=build /app ./

ENTRYPOINT ["dotnet", "ProductCatalogApi.dll", "--server.urls", "http://+:5004"]

my docker-compose.yml file (do not mind the password format):

version: "5.0.4"

networks:
   frontend:
   backend:

services:
   catalog:
      build:
         context: .\src\Services\ProductCatalogApi
         dockerfile: Dockerfile
      image: shoes/catalog
      environment:
         - DatabaseServer=mssqlserver
         - DatabaseName=CatalogDb
         - DatabaseUser=sa
         - DatabasePassword=(passwordhere)
         - ASPNETCORE_URLS=http://+:5004
         - ASPNETCORE_ENVIRONMENT=Production
      container_name: catalogapi
      ports:
         - "5004:80"
      networks:
         - backend
         - frontend
      depends_on:
         - mssqlserver
         
   mssqlserver:
      image: "mcr.microsoft.com/mssql/server:2019-latest"
      ports:
         - "1445:1433"

      container_name: mssqlcontainer
      environment:
         - ACCEPT_EULA=Y
         - SA_PASSWORD=(passwordhere)
         - MSSQL_PID=Developer
      networks:
         - backend

  

CreateHostBuilder in Program.cs:

        private static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                    // webBuilder.UseKestrel(options => { options.Listen(IPAddress.Any, 5000); });
                    webBuilder.UseKestrel().UseUrls(Environment.GetEnvironmentVariable("ASPNETCORE_URLS"));
                });
    }
}

I can’t figure what’s missing or wrong on my configuration that I can’t access the app on my local machine through localhost:5004(or whatever port ex. 5000 )

Note: I run this commands in the following order

  1. docker-compose build
  2. docker-compose up mssqlserver
  3. docker-compose up catalog

Solution

When you set ASPNETCORE_URLS=http://+:5004, your app will listen on port 5004. So that’s the port you should map to a port on the host. You’ve mapped port 80.

Change your docker-compose file to

  ports:
     - "5004:5004"

Now you should be able to access it. Remember that Swagger by default isn’t available in the Production environment, so you won’t be able to use the Swagger pages.

You’ve tried to configure what port the app listens on in a lot of different ways. A good idea might be to remove it all and only configure it in the launchSettings.json file. Then it’ll listen on the port specified in launchSettings.json when you run it locally during development and it’ll listen on port 80 when run in the container.

The reason it’ll listen on port 80 when run in a container is that Microsoft set the ASPNETCORE_URLS environment variable to http://+:80 in the aspnet images.

Answered By – Hans Kilian

Answer Checked By – Senaida (BugsFixing Volunteer)

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