docker visual-studio-2019 c#-8.0 asp.net-core-3.1

Unable to bind to http://localhost:5000 on the IPv6 loopback interface: 'Cannot assign requested address'

I am using asp.net core 3.1 docker enabled project template (VS2019) to develop a web API. There are no compilation errors.

While running the project, in the output window of the VS2019 I see the following message:

Unable to bind to http://localhost:5000 on the IPv6 loopback interface: 'Cannot assign requested address'.
Loaded '/usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.0/System.Collections.NonGeneric.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
Loaded '/usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.0/System.Security.Cryptography.OpenSsl.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
Loaded '/usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.0/System.Security.Cryptography.Encoding.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
Loaded '/usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.0/System.Runtime.Numerics.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
Microsoft.AspNetCore.Server.Kestrel: Warning: Unable to bind to https://localhost:5001 on the IPv6 loopback interface: 'Cannot assign requested address'.
[40m[1m[33mwarn[39m[22m[49m: Microsoft.AspNetCore.Server.Kestrel[0]
      Unable to bind to https://localhost:5001 on the IPv6 loopback interface: 'Cannot assign requested address'.
[40m[32minfo[39m[22m[49m: Microsoft.Hosting.Lifetime[0]
      Now listening on: http://localhost:5000
Microsoft.Hosting.Lifetime: Information: Now listening on: http://localhost:5000
[40m[32minfo[39m[22m[49m: Microsoft.Hosting.Lifetime[0]
      Now listening on: https://localhost:5001
Microsoft.Hosting.Lifetime: Information: Now listening on: https://localhost:5001
Microsoft.Hosting.Lifetime: Information: Application started. Press Ctrl+C to shut down.
[40m[32minfo[39m[22m[49m: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
[40m[32minfo[39m[22m[49m: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
Microsoft.Hosting.Lifetime: Information: Hosting environment: Development
Microsoft.Hosting.Lifetime: Information: Content root path: /src/QueryStack/Author.Query.New.API
[40m[32minfo[39m[22m[49m: Microsoft.Hosting.Lifetime[0]
      Content root path: /src/QueryStack/Author.Query.New.API

Here goes my Docker.develop file:

FROM mcr.microsoft.com/dotnet/core/sdk:3.1
ARG BUILD_CONFIGURATION=Debug
ENV ASPNETCORE_ENVIRONMENT=Development
ENV DOTNET_USE_POLLING_FILE_WATCHER=true    
EXPOSE 80

WORKDIR /src
COPY ["QueryStack/Author.Query.New.API/Author.Query.New.API.csproj", "QueryStack/Author.Query.New.API/"]
COPY ["QueryStack/Author.Query.Persistence/Author.Query.Persistence.csproj", "QueryStack/Author.Query.Persistence/"]
COPY ["Common/Author.Core.Framework/Author.Core.Framework.csproj", "Common/Author.Core.Framework/"]
COPY ["Common/Author.Core.Services.Rediscache/Author.Core.Services.Rediscache.csproj", "Common/Author.Core.Services.Rediscache/"]
COPY ["QueryStack/Author.Query.Domain/Author.Query.Domain.csproj", "QueryStack/Author.Query.Domain/"]
COPY ["Common/Author.Core.Services.Persistence.CosmosDB/Author.Core.Services.Persistence.CosmosDB.csproj", "Common/Author.Core.Services.Persistence.CosmosDB/"]

RUN dotnet restore "QueryStack/Author.Query.New.API/Author.Query.New.API.csproj"
COPY . .
WORKDIR "/src/QueryStack/Author.Query.New.API"
RUN dotnet build --no-restore "Author.Query.New.API.csproj" -c $BUILD_CONFIGURATION

RUN echo "exec dotnet run --no-build --no-launch-profile -c $BUILD_CONFIGURATION --" > /entrypoint.sh

ENTRYPOINT ["/bin/bash", "/entrypoint.sh"]

Can anyone help me here by providing their guidance to fix this issue

Solution

To workaround the issue, add the code ENV ASPNETCORE_URLS=http://+:80 below the other ENV declarations at the top of the Dockerfile.develop file

Dockerfile.develop after:

FROM mcr.microsoft.com/dotnet/core/sdk:3.1
ARG BUILD_CONFIGURATION=Debug
ENV ASPNETCORE_ENVIRONMENT=Development
ENV DOTNET_USE_POLLING_FILE_WATCHER=true  
ENV ASPNETCORE_URLS=http://+:80  
EXPOSE 80

Explanation

Server URLs is one of the ASP.NET Core Web Host configuration values. It uses the environment variable ASPNETCORE_URLS and defaults to http://localhost:5000:

Indicates the IP addresses or host addresses with ports and protocols that the server should listen on for requests.

Key: urls
Type: string
Default: http://localhost:5000
Set using: UseUrls
Environment variable: ASPNETCORE_URLS

See another thread for the meaning of http://+:80: What's the difference between http://*:80 and http://+:80

Update

As @Monsignor has pointed out:

The original issue is caused by an attempt to bind to localhost which AFAIK is not allowed from inside a docker container. But it's perfectly fine to bind to 0.0.0.0, for example.