Salt: 'dockerng' __virtual__ returned False - docker

Question

I have Debian Jessie and I'm trying to manage Docker containers with Salt dockerng. But when I try for example this state:
# file: docker_demo.sls
hello-world:
dockerng.image_present
Then sudo salt '*' state.highstate fails:
----------
ID: hello-world
Function: dockerng.image_present
Result: False
Comment: State 'dockerng.image_present' was not found in SLS 'docker_demo'
Reason: 'dockerng' __virtual__ returned False
Started:
Duration:
Changes:
How can I fix this so dockerng.image_present can pull the image, dockerng.running can run Docker containers etc.?

Answer 1

The dockerng module executed by Salt minion communicates with Docker daemon over REST API using docker-py (not the CLI command docker).
The error message 'dockerng' __virtual__ returned False is a little bit misleading, but if you see the source code, it returns False because it cannot import Pyhon module docker. So this Python package must be installed.
There are packages in Debian repository: python-docker and python3-docker. But both are incompatible with the recent docker-engine (installed from APT repository deb https://apt.dockerproject.org/repo debian-jessie).
So the solution is to uninstall python-docker package if installed and to install the latest docker-py using pip:
sudo apt-get install python-pip
sudo pip install docker-py
Or use this Salt state:
python-pip:
pkg.installed
docker-py:
pip.installed:
- require:
- pkg: python-pip
Or just run
salt myminion pip.install docker-py
The python-docker package from Debian Stretch (now testing, should become Debian stable in 2017) seems to be working OK.