Can't bind localhost:5000, "Cannot assign requested address" on IPv6 loopback

Programming
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1

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I am developing a web API using the ASP.NET Core 3.1 docker enabled project template (VS2019). I have no compilation errors, but when running the project in the output window of VS2019, I receive 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

My Docker.develop file looks like this:

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 provide guidance on how to fix this issue?

2

The issue is that the web API is unable to bind to http://localhost:5000 and https://localhost:5001 on the IPv6 loopback interface. The error message is “Cannot assign requested address”.

To fix this issue, you can try the following steps:

  1. Add the following line to your Dockerfile:

    ENV ASPNETCORE_URLS=http://+:5000;https://+:5001

    This will configure ASP.NET Core to listen on all available network interfaces, including the IPv4 loopback interface.

  2. Change the EXPOSE command in your Dockerfile to:

    EXPOSE 5000 5001

    This will expose ports 5000 and 5001 to the Docker host.

  3. Modify the entrypoint.sh file to include the ASP.NET Core URL configuration:

    exec dotnet run --no-build --no-launch-profile -c $BUILD_CONFIGURATION --urls=http://+:5000;https://+:5001

    This will configure the ASP.NET Core runtime to listen on all available network interfaces, including the IPv4 loopback interface.

Once you have made these changes, rebuild your Docker image and run the container. The web API should now be able to bind to http://localhost:5000 and https://localhost:5001 on the IPv4 loopback interface.