Docker build抱怨找不到nuget fallback包文件夹

Question

我正在通过https://docs.microsoft.com/zh-cn/dotnet/core/docker/docker-basics-dotnet-core#dockerize-the-net-core-application上的教程学习如何容器化.net核心应用程序纳入Docker。

除了将Dockerfileto Point指向microsoft/dotnet:2.1-sdk为基础图像，并添加RUN dotnet --info一行以获取版本/环境信息外，其他所有内容都是相同的。但是，我在dotnet publish步骤上遇到错误：

Step 7/8 : RUN dotnet publish -c Release -o out
 ---> Running in 6739267c7581
Microsoft (R) Build Engine version 15.8.166+gd4e8d81a88 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 34.46 ms for /app/Hello.csproj.
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018: The "ResolvePackageAssets" task failed unexpectedly. [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018: NuGet.Packaging.Core.PackagingException: Unable to find fallback package folder 'C:\Program Files\dotnet\sdk\NuGetFallbackFolder'. [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at NuGet.Packaging.FallbackPackagePathResolver..ctor(String userPackageFolder, IEnumerable`1 fallbackPackageFolders) [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.NuGetPackageResolver.CreateResolver(LockFile lockFile, String projectPath) [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.CacheWriter..ctor(ResolvePackageAssets task, Stream stream) [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.CacheReader.CreateReaderFromDisk(ResolvePackageAssets task, Byte[] settingsHash) [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.CacheReader..ctor(ResolvePackageAssets task) [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ReadItemGroups() [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ExecuteCore() [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.NET.Build.Tasks.TaskBase.Execute() [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() [/app/Hello.csproj]
/usr/share/dotnet/sdk/2.1.401/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(198,5): error MSB4018:    at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask) [/app/Hello.csproj]
The command '/bin/sh -c dotnet publish -c Release -o out' returned a non-zero code: 1

到目前为止，我在该主题上唯一能找到的就是一些github问题，要求在Docker容器膨胀时将fallback文件夹丢弃在Docker中。在这个阶段，我不太关心膨胀，我只是希望它构建一个hello world应用程序。

---

如果有帮助，该dotnet --info命令将返回以下内容：

Step 3/8 : RUN dotnet --info
 ---> Running in 17dad2f04a7e
.NET Core SDK (reflecting any global.json):
 Version:   2.1.401
 Commit:    91b1c13032

Runtime Environment:
 OS Name:     debian
 OS Version:  9
 OS Platform: Linux
 RID:         debian.9-x64
 Base Path:   /usr/share/dotnet/sdk/2.1.401/

Host (useful for support):
  Version: 2.1.3
  Commit:  124038c13e

.NET Core SDKs installed:
  2.1.401 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.3 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

Answer 1

问题是 bin 和 obj 目录中存在一些遗留文件，您不需要从源代码构建应用程序。因此，我认为最好的解决方案是将 bin 和 obj 目录添加到 .dockerignore 文件中，这将排除这些文件夹复制到您的 Docker 上下文中，从而导致性能的小幅提升。这是我的 .dockerignore 文件对于 dotnet 应用程序的样子：

.dockerignore
.env
.git
.gitignore
.vs
.vscode
docker-compose.yml
docker-compose.*.yml
**/bin
**/obj
bin/
obj/

Answer 2

这可能是由于obj\project.assests.json打开项目时Visual Studio生成的文件所致。如果在其中查找，则会在Windows系统中找到对NuGet软件包文件夹的引用。

例如

"packageFolders": {
  "C:\\Users\\<UserName>\\.nuget\\packages\\": {},
  "C:\\Program Files\\dotnet\\sdk\\NuGetFallbackFolder": {}
},

一个简单的解决方法是在您的Dockerfile中添加一个步骤，以删除bin和obj文件，然后再运行任何还原，构建或测试步骤。一种方法是利用find程序：

find -type d -name bin -prune -exec rm -rf {} \; && find -type d -name obj -prune -exec rm -rf {} \;

以您链接到的教程中的Dockerfile为例，它看起来像这样：

FROM microsoft/dotnet:2.1-sdk
WORKDIR /app

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

# copy and build everything else
COPY . ./
RUN find -type d -name bin -prune -exec rm -rf {} \; && find -type d -name obj -prune -exec rm -rf {} \;
RUN dotnet publish -c Release -o out
ENTRYPOINT ["dotnet", "out/Hello.dll"]