来自 Docker 容器的 dotnet restore 失败

Question

过去几天我一直在研究这个，我发现的研究都没有帮助我解决这个问题，包括重新启动 Docker、重新启动 Docker 服务、重新启动 Visual Studio、删除 Nuget、调整代理设置、调整 Nuget.config 等.

最终，我得到的错误消息是，Unable to load the service index for source https://api.nuget.org/v3/index.json.但请耐心等待，我正在给出重现此错误的具体步骤。

当我在 Visual Studio 2019 中创建 ASP.NET Core Web 应用程序，然后向项目添加 Docker 支持（右键单击项目，选择添加 -> Docker 支持...）时，会创建一个 Dockerfile，如下所示：

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-nanoserver-1809 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/core/sdk:3.1-nanoserver-1809 AS build
WORKDIR /src
COPY ["WebApplication3/WebApplication3.csproj", "WebApplication3/"]
RUN dotnet restore "WebApplication3/WebApplication3.csproj"
COPY . .
WORKDIR "/src/WebApplication3"
RUN dotnet build "WebApplication3.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "WebApplication3.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "WebApplication3.dll"]

当我构建 docker 镜像时（右键单击 dockerfile，选择 Build Docker Image），它构建得很好，我得到：

Starting up container(s)...
docker build -f "C:\Users\TheUser\source\repos\WebApplication3\WebApplication3\Dockerfile" --force-rm -t webapplication3:dev --target base  --label "com.microsoft.created-by=visual-studio" --label "com.microsoft.visual-studio.project-name=WebApplication3" "C:\Users\TheUser\source\repos\WebApplication3" 
Sending build context to Docker daemon  4.396MB

Step 1/6 : FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-nanoserver-1809 AS base
 ---> dc28376d4369
Step 2/6 : WORKDIR /app
 ---> Using cache
 ---> d0cbefb504d1
Step 3/6 : EXPOSE 80
 ---> Using cache
 ---> 865f960359d6
Step 4/6 : EXPOSE 443
 ---> Using cache
 ---> 4d040d5c8a4c
Step 5/6 : LABEL com.microsoft.created-by=visual-studio
 ---> Using cache
 ---> 4223be37abec
Step 6/6 : LABEL com.microsoft.visual-studio.project-name=WebApplication3
 ---> Running in d1ced38ba0fa
Removing intermediate container d1ced38ba0fa
 ---> fb400230edf4
Successfully built fb400230edf4
Successfully tagged webapplication3:dev
docker run -dt -v "C:\Users\TheUser\onecoremsvsmon\16.4.0067.0:C:\remote_debugger:ro" -v "C:\Users\TheUser\source\repos\WebApplication3\WebApplication3:C:\app" -v "C:\Users\TheUser\source\repos\WebApplication3:C:\src" -v "C:\Users\TheUser\AppData\Roaming\Microsoft\UserSecrets:C:\Users\ContainerUser\AppData\Roaming\Microsoft\UserSecrets:ro" -v "C:\Users\TheUser\AppData\Roaming\ASP.NET\Https:C:\Users\ContainerUser\AppData\Roaming\ASP.NET\Https:ro" -v "C:\Users\TheUser\.nuget\packages\:c:\.nuget\fallbackpackages2" -v "C:\Program Files\dotnet\sdk\NuGetFallbackFolder:c:\.nuget\fallbackpackages" -e "DOTNET_USE_POLLING_FILE_WATCHER=1" -e "ASPNETCORE_ENVIRONMENT=Development" -e "ASPNETCORE_URLS=https://+:443;http://+:80" -e "NUGET_PACKAGES=c:\.nuget\fallbackpackages2" -e "NUGET_FALLBACK_PACKAGES=c:\.nuget\fallbackpackages;c:\.nuget\fallbackpackages2" -P --name WebApplication3 --entrypoint C:\remote_debugger\x64\msvsmon.exe webapplication3:dev /noauth /anyuser /silent /nostatus /noclrwarn /nosecuritywarn /nofirewallwarn /nowowwarn /fallbackloadremotemanagedpdbs /timeout:2147483646 /LogDebuggeeOutputToStdOut 
eba5dec02ed7a80158340d6f8d6af504b86edf7cd6944eb1d4ce71f7847fabb5
Container started successfully.
========== Finished ==========

但是，如果我将 .Net Core 类库添加到解决方案中，将该类库添加为对 Web 应用程序的项目引用并再次添加 Docker 支持，则会得到一个新的 Dockerfile，如下所示：

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-nanoserver-1809 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/core/sdk:3.1-nanoserver-1809 AS build
WORKDIR /src
COPY ["WebApplication3/WebApplication3.csproj", "WebApplication3/"]
COPY ["ClassLibrary1/ClassLibrary1.csproj", "ClassLibrary1/"]
RUN dotnet restore "WebApplication3/WebApplication3.csproj"
COPY . .
WORKDIR "/src/WebApplication3"
RUN dotnet build "WebApplication3.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "WebApplication3.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "WebApplication3.dll"]

当我再次构建 Docker Image 时，我收到一个错误，如下所示：

1>------ Rebuild All started: Project: ClassLibrary1, Configuration: Debug Any CPU ------
1>ClassLibrary1 -> C:\Users\TheUser\source\repos\WebApplication3\ClassLibrary1\bin\Debug\netcoreapp3.1\ClassLibrary1.dll
2>------ Rebuild All started: Project: WebApplication3, Configuration: Debug Any CPU ------
2>docker rm -f eba5dec02ed7a80158340d6f8d6af504b86edf7cd6944eb1d4ce71f7847fabb5
2>eba5dec02ed7a80158340d6f8d6af504b86edf7cd6944eb1d4ce71f7847fabb5
2>WebApplication3 -> C:\Users\TheUser\source\repos\WebApplication3\WebApplication3\bin\Debug\netcoreapp3.1\WebApplication3.dll
2>WebApplication3 -> C:\Users\TheUser\source\repos\WebApplication3\WebApplication3\bin\Debug\netcoreapp3.1\WebApplication3.Views.dll
2>Docker version 19.03.8, build afacb8b
2>docker build -f "c:\users\TheUser\source\repos\webapplication3\webapplication3\dockerfile" --force-rm -t webapplication3  --label "com.microsoft.created-by=visual-studio" --label "com.microsoft.visual-studio.project-name=WebApplication3" "c:\users\TheUser\source\repos\webapplication3"
2>Sending build context to Docker daemon    4.4MB
2>
2>Step 1/20 : FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-nanoserver-1809 AS base
2> ---> dc28376d4369
2>Step 2/20 : WORKDIR /app
2> ---> Using cache
2> ---> d0cbefb504d1
2>Step 3/20 : EXPOSE 80
2> ---> Using cache
2>Step 4/20 : EXPOSE 443
2> ---> 865f960359d6
2> ---> Using cache
2> ---> 4d040d5c8a4c
2>Step 5/20 : FROM mcr.microsoft.com/dotnet/core/sdk:3.1-nanoserver-1809 AS build
2> ---> c67fa4d2a089
2>Step 6/20 : WORKDIR /src
2> ---> Using cache
2> ---> 14763e98238e
2>Step 7/20 : COPY ["WebApplication3/WebApplication3.csproj", "WebApplication3/"]
2> ---> ad0ded95d169
2>Step 8/20 : COPY ["ClassLibrary1/ClassLibrary1.csproj", "ClassLibrary1/"]
2> ---> 22667eda405c
2>Step 9/20 : RUN dotnet restore "WebApplication3/WebApplication3.csproj"
2> ---> Running in a3e6a184b4e9
2>  Restore completed in 495.4 ms for C:\src\ClassLibrary1\ClassLibrary1.csproj.
2>C:\Program Files\dotnet\sdk\3.1.201\NuGet.targets(124,5): error : Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\src\WebApplication3\WebApplication3.csproj]
2>C:\Program Files\dotnet\sdk\3.1.201\NuGet.targets(124,5): error :   No such host is known. [C:\src\WebApplication3\WebApplication3.csproj]
2>Removing intermediate container a3e6a184b4e9
2>The command 'cmd /S /C dotnet restore "WebApplication3/WebApplication3.csproj"' returned a non-zero code: 1
2>c:\users\TheUser\source\repos\webapplication3\webapplication3\dockerfile : error CTC1014: Docker command failed with exit code 1.
2>c:\users\TheUser\source\repos\webapplication3\webapplication3\dockerfile : error CTC1014: The command 'cmd /S /C dotnet restore "WebApplication3/WebApplication3.csproj"' returned a non-zero code: 1
2>Done building project "WebApplication3.csproj" -- FAILED.
========== Rebuild All: 1 succeeded, 1 failed, 0 skipped ==========

应该很容易重现。为什么它在没有类库引用的情况下工作，然后在添加引用时出错？我需要用额外的东西更新 Dockerfile 吗？我一直在绕圈子，关于这个主题的其他帖子都没有用这种方式表达或给我任何对我有用的答案。

Answer 1

实际的错误似乎是：

Unable to load the service index for source https://api.nuget.org/v3/index.json

这意味着 nuget 在尝试下载依赖项时无法访问端点。

这里列出了许多解决方案

https://github.com/NuGet/Home/issues/2880

并且

Nuget 连接尝试失败“无法加载源的服务索引”