Jenkins, Docker agents, and /etc/environment

[Zach LaCelle]

I have some proxy settings defined in the /etc/environment files of my
Docker images which constitute my Jenkins agents. These images are
correctly spun up and Jenkins happily builds within them, with one issue:
the variables from /etc/environment aren't present in the agent environment.

When I run "docker run -it myimage /bin/bash" I can see the variables set
correctly.

When I run "env" within a Jenkins build, they are not.

I understand that Jenkins launches non-interactive shells, but these should
still read /etc/environment, I believe.

What is the best way to get Jenkins agents to respect environment variables
from the system? Is there a better option than /etc/environment?