How to configure docker container proxy?

you need instruct the apt script to connect through proxy inside the container

# echo 'Acquire::http::proxy "proxy:port/";' > /etc/apt/apt.conf.d/40proxy

remember, this should be written inside the container

and in the machine that have docker running, the proxy should be configured like people said before in their comments

You can set the proxy environment variables when starting the container, for example:

docker container run \
  -e HTTP_PROXY=http://username:[email protected] \
  -e HTTPS_PROXY=http://username:[email protected] \
  myimage

If you want the proxy-server to be automatically used when starting a container, you can configure default proxy-servers in the Docker CLI configuration file (~/.docker/config.json). You can find instructions for this in the networking section in the user guide.

For example:

{
  "proxies": {
    "default": {
      "httpProxy": "http://username:[email protected]",
      "httpsProxy": "http://username:[email protected]"
    }
  }
}

To verify if the ~/.docker/config.json configuration is working, start a container and print its env:

docker container run --rm busybox env

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=220e4df13604
HTTP_PROXY=http://username:[email protected]
http_proxy=http://username:[email protected]
HTTPS_PROXY=http://username:[email protected]
https_proxy=http://username:[email protected]
HOME=/root