The value goes from a YAML file from discourse_docker (which is in my control and is quoted and therefore correctly goes) to an environment variable inside the container. The environment shows the correct value. From that point it goes to Ruby (not in my control), and judging by the comments in config/application.yml about the production rails environment, probably not via YAML again. Regardless, I did my end right - this is a bug, and clearly fixable as evidenced by the fact that rake db:migrate was still able to work. 