title: Docker build complains it can't find nuget fallback package folder
body: <p>I'm following the tutorial at <a href="https://docs.microsoft.com/en-us/dotnet/core/docker/docker-basics-dotnet-core#dockerize-the-net-core-application" rel="noreferrer">https://docs.microsoft.com/en-us/dotnet/core/docker/docker-basics-dotnet-core#dockerize-the-net-core-application</a> in learning to containerise .net core applications into Docker.</p>
  
  <p>Other than changing the <code>Dockerfile</code> to point at <code>microsoft/dotnet:2.1-sdk</code> as a base image, and adding a <code>RUN dotnet --info</code> line to get version/environment information, everything else is the same. However, I'm getting an error on the <code>dotnet publish</code> step:</p>
  
  <pre><code>Step 7/8 : RUN dotnet publish -c Release -o out
   ---&gt; 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
  </code></pre>
  
  <p>So far the only thing I can find on the subject is some github issues requesting that the fallback folder is ditched in Docker as it bloats the container. At this stage I'm not concerned too much about bloat, I just want it to build a hello world application.</p>
  
  <hr>
  
  <p>In case it is helpful the <code>dotnet --info</code> command returned the following:</p>
  
  <pre><code>Step 3/8 : RUN dotnet --info
   ---&gt; 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
  </code></pre>