Docker for Windows building added prefix `/var/lib/docker/tmp/` for COPY?

Question

I've installed Docker for Windows and created a new Asp.net core application with docker support using Visual Studio 2017(I haven't made any change yet). However, docker build reported the following error. Is the Dockerfile correct?

PS C:\source\repos\myProj\ProcessFiles> docker build .
Sending build context to Docker daemon  1.178MB
Step 1/17 : FROM microsoft/dotnet:2.1-aspnetcore-runtime AS base
 ---> 04aae08f15c5
Step 2/17 : WORKDIR /app
 ---> Using cache
 ---> 135955e04284
Step 3/17 : EXPOSE 34746
 ---> Using cache
 ---> 85fd0075aa42
Step 4/17 : EXPOSE 44398
 ---> Using cache
 ---> 7e3d5526f601
Step 5/17 : FROM microsoft/dotnet:2.1-sdk AS build
 ---> 7c3e298d40ac
Step 6/17 : WORKDIR /src
 ---> Using cache
 ---> b395ba27d8f9
Step 7/17 : COPY ProcessFiles/ProcessFiles.csproj ProcessFiles/
COPY failed: stat /var/lib/docker/tmp/docker-builder662645761/ProcessFiles/ProcessFiles.csproj: no such file
 or directory

Here is the Dockerfile automatically generated by Visual Studio. The error occurred on the line COPY ProcessFiles/ProcessFiles.csproj ProcessFiles/.

FROM microsoft/dotnet:2.1-aspnetcore-runtime AS base
WORKDIR /app
EXPOSE 34746
EXPOSE 44398

FROM microsoft/dotnet:2.1-sdk AS build
WORKDIR /src
COPY ProcessFiles/ProcessFiles.csproj ProcessFiles/
RUN dotnet restore ProcessFiles/ProcessFiles.csproj
COPY . .
WORKDIR /src/ProcessFiles
RUN dotnet build ProcessFiles.csproj -c Release -o /app

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

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

Here is the Visual Studio output. (The lines about setting AWS were excluded).

Inspecting Dockerfile to figure how to build project and docker image
... Skip building project since it is done as part of Dockerfile
Executing docker build
... invoking 'docker build', working folder 'C:\source\repos\myProj\ProcessFiles, docker file C:\source\repos\myProc\ProcessFiles\Dockerfile, image name processfiles:latest'
... docker build: Sending build context to Docker daemon  1.178MB
... docker build: COPY failed: stat /var/lib/docker/tmp/docker-builder225959758/ProcessFiles/ProcessFiles.csproj: no such file or directory
... docker build: Step 1/17 : FROM microsoft/dotnet:2.1-aspnetcore-runtime AS base
... docker build:  ---> 04aae08f15c5
... docker build: Step 2/17 : WORKDIR /app
... docker build:  ---> Using cache
... docker build:  ---> 135955e04284
... docker build: Step 3/17 : EXPOSE 34746
... docker build:  ---> Using cache
... docker build:  ---> 85fd0075aa42
... docker build: Step 4/17 : EXPOSE 44398
... docker build:  ---> Using cache
... docker build:  ---> 7e3d5526f601
... docker build: Step 5/17 : FROM microsoft/dotnet:2.1-sdk AS build
... docker build:  ---> 7c3e298d40ac
... docker build: Step 6/17 : WORKDIR /src
... docker build:  ---> Using cache
... docker build:  ---> b395ba27d8f9
... docker build: Step 7/17 : COPY ProcessFiles/ProcessFiles.csproj ProcessFiles/
Error executing "docker build"
Attempting to clean up any ELB resources created for the failed deployment
Unknown error publishing container to AWS

Here are the files in directory C:\source\repos\myProj. The file Dockerfile is under C:\source\repos\myProj\ProcessFile\. Should it be moved one level up?

Mode   Name
----   ----
d----- bin
d----- obj
d----- ProcessFiles
-a---- .dockerignore
-a---- .gitattributes
-a---- .gitignore
-a---- docker-compose.dcproj
-a---- docker-compose.override.yml
-a---- docker-compose.yml
-a---- myProc.sln

BMitch BMitch · Accepted Answer · 2018-06-14T13:18:25

When you run the build command

docker build .

The . in that command indicates the "build context" that gets sent to the (possibly remote) docker engine. All of the COPY and ADD commands must be from inside this directory (or from a previous stage with multi stage builds). You can also exclude files from this context using the .dockerignore file. The tmp directory is a uniquely generated internal directory of docker's consisting of this build context.

To fix your issue, you need to make sure ProcessFiles/ProcessFiles.csproj exists in the directory where you run your build from, and that you didn't exclude it from the context with the .dockerignore file.

Edit: based on your comments, change your copy command to:

COPY ProcessFiles.csproj ProcessFiles/

Docker for Windows building added prefix `/var/lib/docker/tmp/` for COPY?

2 Answers