Setting variable in /etc/environment has no effect

I have the following in my /etc/environment:

http_proxy=http://myproxy.net:12345

After rebooting the machine, I login and check the variable:

root@d6c44fa03243:/# echo $http_proxy
(empty)

Why is the variable not set?

Note: I must mention that this is a docker container, although I do not see why it would make a difference.

EDIT

More details about the system (Ubuntu 16.04.4 Xenial Xerus):

root@d6c44fa03243:/# uname -a
Linux d6c44fa03243 4.4.0-116-generic #140-Ubuntu SMP Mon Feb 12 21:23:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

root@d6c44fa03243:/# cat /etc/issue
Ubuntu 16.04.4 LTS \n \l

EDIT2

According to the Ubuntu documentation:

/etc/environment

This file is specifically meant for system-wide environment variable settings. It is not a script file, but rather consists of assignment expressions, one per line.

Because UNIX tools are built with transparency in mind, you can find the answer with the help of grep. It doesn't matter if you are working with a full OS or a container (the later just means it you might have to take some extra steps to install tools you need for things to become transparent).

Check that you have grep installed on your OS and run sudo grep -R "/etc/environment" /etc/*. This will search all the system scripts and configurations to see which ones use use this file. On a default ubuntu/xenial64 vagrant box, the scripts and configurations that use this file are mostly in /etc/init.d/ /etc/pam.d/, and /etc/rc.*.d/.

The following configurations are how variables in /etc/environment get set in my shell:

/etc/pam.d/login /etc/pam.d/su /etc/pam.d/sshd

From man pam_env:

The pam_env PAM module allows the (un)setting of environment variables. ...

This module can also parse a file with simple KEY=VAL pairs on separate lines (/etc/environment by default). You can change the default file to parse, with the envfile flag and turn it on or off by setting the readenv flag to 1 or 0 respectively. ...

Do a similar search on your docker container. You can check if your container uses pam_env.so.

Most likely the best solution is to have your start up process create environment variables from /etc/environment but that advice is given without understanding what you are building. The uses in `/etc/rc*.d/ might be good examples for how to accomplish this.

Most people follow @ben-njeri's advice and set variables in the default configuration files for the bash shell.

I have (had) this problem on Ubuntu 18.04. I couldn't get /etc/environment to work at all, but used a script in /etc/profile.d/ instead (as documented here), and that did work.

For more info, see my answer to this related question. Hope it helps :)