Working behind a proxy is always a bit of a pain. Luckly if you are doing so work with Docker behind a proxy you've come to the right place. Below steps should allow your docker instance to shot out to the internet to get images. Note, I will go about how to do this with systemd. You will need to adapt this slightly if using a different init system.
First make the following directory
Then create a http-proxy.conf file under this directory. This conf file will hold the proxy details. The content as follows:
Take note, if you have a local docker registry that you don't want to go through the proxy you can set a no proxy option like so:
Essentially place the dns names or ips of the address you don't want to go through the proxy.
Once this is done simply flush your changes:
sudo systemctl daemon-reload
You can verify these changes have been applied via:
systemctl show --property Environment docker
Finally restart docker
systemctl restart docker
You should now be able to pull your images from your proxy.