Proxy settings for apt-get are lowercase! !! !! !! !!

I sometimes wanted to build a Docker image under a proxy environment, so I made it possible to set proxy information in ARG.

FROM debian

#Specify when building in a proxy environment
ARG HTTP_PROXY
ARG HTTPS_PROXY

RUN apt-get update \
 && apt-get install -y ... \
 && rm -rf /var/lib/apt/lists/*

$ docker build --build-arg HTTP_PROXY=... --build-arg HTTPS_PROXY=... .
(Abbreviation)
Err:1 http://deb.debian.org/debian buster InRelease
  Cannot initiate the connection to prod.debian.map.fastly.net:80 (2a04:4e42:1a::204). - connect (101: Network is unreachable) Could not connect to prod.debian.map.fastly.net:80 (151.101.108.204), connection timed out
  Cannot initiate the connection to deb.debian.org:80 (2a04:4e42:1a::645). - connect (101: Network is unreachable) Could not connect to deb.debian.org:80 (151.101.110.133), connection timed out

What? I can't go through a proxy.

Here is the correct answer that I found after half a day worrying about why this did not work.

FROM debian

#Specify when building in a proxy environment
ARG http_proxy
ARG https_proxy

RUN apt-get update \
 && apt-get install -y ... \
 && rm -rf /var/lib/apt/lists/*

$ docker build --build-arg http_proxy=... --build-arg https_proxy=... .

The cause of the defeat is the belief that "environment variables are specified in uppercase letters" and "environment variables cannot be Case Sensitive".

Dear Sir, Be careful when using apt-get in a proxy environment.