It had to do with the fact that I am using an anaconda environment inside the docker container and miniconda as base image. Adding to the ENTRYPOINT conda python in my dockerfile the --no-capture-output flag solved the problem.
In my setups, I run a linux supervisor, that controls gunicorn, which is configured to take the print outs to a file. This is especially helpful for when you are running the application in a permanent install.
ah right, now I got you. In my setup I run a systemd service that starts a docker container on server boot. Inside the container is my miniconda and dash is started by gunicorn as well.
I’ll have a look at your setup. Thanks for the inspiration!