PROXY is not working inside windows container

Question

I'm using windows containers in windows 10. I've set proxy variables(HTTP_PROXY,HTTPS_PROXY) in environmental variable setup and using VPN. I also configured resources -> Proxies.

I was trying to build docker image with following Dockerfile content.

FROM mcr.microsoft.com/windows/servercore:ltsc2019
SHELL ["cmd", "/S", "/C"]

RUN mkdir c:\temp \
    && curl -SL --output c:\temp\vs_buildtools.exe https://aka.ms/vs/16/release/vs_buildtools.exe

When this docker image build command is executed it shows following error.

Step 5/5 : RUN mkdir c:\temp     && curl -SL --output c:\temp\vs_buildtools.exe https://aka.ms/vs/16/release/vs_buildtools.exe
 ---> Running in 0c134b2d004a
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:12 --:--:--     0curl: (6) Could not resolve host: aka.ms
The command 'cmd /S /C mkdir c:\temp     && curl -SL --output c:\temp\vs_buildtools.exe https://aka.ms/vs/16/release/vs_buildtools.exe' returned a non-zero code: 6

I tried to build this with build arguments, and added dns: 8.8.8.8 in docker deamon config file

docker build --build-arg HTTP_PROXY --build-arg HTTPS_PROXY --tag=tswin .

But above mentioned error is not solved.

When the same curl command is executed in Windows's CMD it is not throwing any error

C:\Users\mshanm6x>curl -SL --output c:\temp\vs_buildtools.exe https://aka.ms/vs/16/release/vs_buildtools.exe
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:01 --:--:--     0
100 1432k  100 1432k    0     0   238k      0  0:00:06  0:00:06 --:--:--  332k

Also the same Dockerfile was able to built by without HTTP_PROXY, HTTPS_PROXY env variables and VPN off.

What is the real issue. Why it is not working inside of container with proxy configuration.

Answer 1

I had the same problem and I found that you have to specify the proxy address also in the curl command.

So your Dockerfile become

FROM mcr.microsoft.com/windows/servercore:ltsc2019

ENV HTTP_PROXY=$HTTP_PROXY
ENV HTTPS_PROXY=$HTTPS_PROXY

SHELL ["cmd", "/S", "/C"]

RUN mkdir c:\temp \
    && curl -SL --output c:\temp\vs_buildtools.exe https://aka.ms/vs/16/release/vs_buildtools.exe --proxy %HTTP_PROXY%

and you will have to call the build command with this instruction

docker build --build-arg HTTP_PROXY --build-arg HTTPS_PROXY --tag=tswin .