Docker & Ansible on RHEL / CentOS 7

We use Ansible to deploy Docker containers on our systems and the infrastructures of our customers. This works pretty well if your system is configured properly.

Here’s a simple playbook to run the hello-world Docker container on one of your systems:

---
- hosts: docker.confirm.ch
  tasks:
    - name: run hello-world docker container
      docker:
        name: hello-world
        image: hello-world
        state: present
  sudo: yes

Dependency to docker-py

Ansible is written in Python, so is the docker module. Therefor it makes use of the docker-py Python library to manage containers.

To use Ansible’s docker module, you’ve to make sure the docker-py library is installed. We do that by creating a new Ansible role named docker and then add the installation of the required packages (docker, docker-py) as a task. Now every role which uses Ansible’s docker module adds our docker role as dependency, therefor the docker and docker-py packages are installed automatically.

This is where the problem starts on RHEL or CentOS 7, because docker-py is available via PyPi, therefor pip and finally via yum / RHN channels as well.

The RPM

When you install the docker-py module via yum, you’ll end up with something like this:

# rpm -qi docker-python
Name        : docker-python
Version     : 1.4.0
Release     : 108.el7
Architecture: x86_64
Install Date: Thu 03 Sep 2015 09:47:59 AM CEST
Group       : Unspecified
Size        : 180199
License     : ASL 2.0
Signature   : RSA/SHA256, Wed 29 Jul 2015 07:15:07 AM CEST, Key ID 199e2f91fd431d51
Source RPM  : docker-1.7.1-108.el7.src.rpm
Build Date  : Tue 28 Jul 2015 10:09:38 PM CEST
Build Host  : x86-030.build.eng.bos.redhat.com
Relocations : (not relocatable)
Packager    : Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>
Vendor      : Red Hat, Inc.
URL         : http://www.docker.com
Summary     : An API client for docker written in Python
Description :
An API client for docker written in Python

As you can see the version 1.4.0 is installed. This can also be verified via pip and python’s help() or pydoc:

# pip list | grep docker
docker-py (1.4.0-dev)

# pydoc docker
Help on package docker:

NAME
    docker - # Copyright 2013 dotCloud inc.

FILE
    /usr/lib/python2.7/site-packages/docker/__init__.py

PACKAGE CONTENTS
    auth (package)
    client
    clientbase
    constants
    errors
    ssladapter (package)
    tls
    unixconn (package)
    utils (package)
    version

DATA
    __title__ = 'docker-py'
    __version__ = '1.4.0-dev'
    version = '1.4.0-dev'
    version_info = (1, 4, 0)

VERSION
    1.4.0-dev

This looks quite ok, but there’s something really strange, because there is no official 1.4.0(-dev) version on PyPi or even github.
There’s a 1.4.0-dev version available on PyPi, but it’s an inofficial version from a user called sunadm.

But let’s ignore that for now, because here’s the real issue with the official docker-py RPM from Red Hat:
If you run the Ansible playbook above with the RPM docker-py-1.4.0-108.el7 installed, you’ll get a Python error / traceback:

Traceback (most recent call last):
  File "/home/ansible/.ansible/tmp/ansible-tmp-1441276343.36-208631949891601/docker", line 3132, in <module>
    main()
  File "/home/ansible/.ansible/tmp/ansible-tmp-1441276343.36-208631949891601/docker", line 1464, in main
    check_dependencies(module)
  File "/home/ansible/.ansible/tmp/ansible-tmp-1441276343.36-208631949891601/docker", line 482, in check_dependencies
    versioninfo = get_docker_py_versioninfo()
  File "/home/ansible/.ansible/tmp/ansible-tmp-1441276343.36-208631949891601/docker", line 458, in get_docker_py_versioninfo
    version.append(int(digit))
ValueError: invalid literal for int() with base 10: '0-de'

The PyPi package

Now you might just want to remove the RPM and install docker-py via PyPi / pip .
That’s a good idea, let’s see how that works out:

# remove RPM
yum -y remove docker-python

# install pip package (1.2.3 is tested and works with Ansible)
pip install docker-py==1.2.3

Run Ansible again and you’ll catch another traceback:

Traceback (most recent call last):
 File "/home/ansible/.ansible/tmp/ansible-tmp-1441276636.72-115693703488445/docker", line 3132, in <module>
 main()
 File "/home/ansible/.ansible/tmp/ansible-tmp-1441276636.72-115693703488445/docker", line 1436, in main
 docker_api_version = dict(required=False, default=DEFAULT_DOCKER_API_VERSION, type='str'),
NameError: global name 'DEFAULT_DOCKER_API_VERSION' is not defined

While the traceback was raised by Ansible, the root cause is within the docker.client module.
Though Ansible isn’t handling exceptions properly there – especially if docker-py isn’t installed at all 😉

Let’s dig into the problem by having a look at Ansible’s docker module.
Around line 428 you’ll see the import statements for the Python docker modules / classes:

import sys
import json
import os
import shlex
from urlparse import urlparse
try:
    import docker.client
    import docker.utils
    import docker.errors
    from requests.exceptions import RequestException
except ImportError:
    HAS_DOCKER_PY = False

if HAS_DOCKER_PY:
    try:
        from docker.errors import APIError as DockerAPIError
    except ImportError:
        from docker.client import APIError as DockerAPIError
    try:
        # docker-py 1.2+
        import docker.constants
        DEFAULT_DOCKER_API_VERSION = docker.constants.DEFAULT_DOCKER_API_VERSION
    except (ImportError, AttributeError):
        # docker-py less than 1.2
        DEFAULT_DOCKER_API_VERSION = docker.client.DEFAULT_DOCKER_API_VERSION

Later in that file around line 1638 you’ll see a dict which makes use of the DEFAULT_DOCKER_API_VERSION variable:

docker_api_version = dict(required=False, default=DEFAULT_DOCKER_API_VERSION, type='str'),

And exactly this line will raise our exception above, because DEFAULT_DOCKER_API_VERSION isn’t defined.
This happens because there was an ImportError while importing the docker.client class.

You can reproduce that by executing:

# python
Python 2.7.5 (default, Apr  9 2015, 11:03:32)
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import docker.client
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/docker/__init__.py", line 20, in <module>
    from .client import Client, AutoVersionClient # flake8: noqa
  File "/usr/lib/python2.7/site-packages/docker/client.py", line 37, in <module>
    import websocket
  File "/usr/lib/python2.7/site-packages/websocket/__init__.py", line 22, in <module>
    from ._core import *
  File "/usr/lib/python2.7/site-packages/websocket/_core.py", line 41, in <module>
    from ._url import *
  File "/usr/lib/python2.7/site-packages/websocket/_url.py", line 23, in <module>
    from six.moves.urllib.parse import urlparse
ImportError: No module named urllib.parse

Python six dependency

The root cause is within the dependencies of the docker-py module / docker.client class.
Docker-py requires six, which is another Python library. By default RHEL / CentOS 7 provide six via RPM:

# rpm -qi python-six
Name        : python-six
Version     : 1.3.0
Release     : 4.el7
Architecture: noarch
Install Date: Mon 31 Aug 2015 11:08:51 AM CEST
Group       : Development/Languages
Size        : 51382
License     : MIT
Signature   : RSA/SHA256, Wed 02 Apr 2014 09:11:29 PM CEST, Key ID 199e2f91fd431d51
Source RPM  : python-six-1.3.0-4.el7.src.rpm
Build Date  : Sun 29 Dec 2013 03:36:45 PM CET
Build Host  : x86-020.build.eng.bos.redhat.com
Relocations : (not relocatable)
Packager    : Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>
Vendor      : Red Hat, Inc.
URL         : http://pypi.python.org/pypi/six/
Summary     : Python 2 and 3 compatibility utilities
Description :
python-six provides simple utilities for wrapping over differences between
Python 2 and Python 3.

This is the Python 2 build of the module.

# pip list | grep six
six (1.3.0)

When you’ve a look at PyPi, you’ll see that the version 1.3.0 is relatively old (2013-03-18).
Though RedHat isn’t currently providing any newer version of the package and unfortunately it’s required for other RPMs as well:

=====================================================================================================================
 Package                           Arch           Version                 Repository                            Size
=====================================================================================================================
Removing:
 python-six                        noarch         1.3.0-4.el7             @rhel-server-7                 50 k
Removing for dependencies:
 abrt                              x86_64         2.1.11-22.el7_1         @rhel-server-7                2.2 M
 abrt-addon-ccpp                   x86_64         2.1.11-22.el7_1         @rhel-server-7                331 k
 abrt-addon-kerneloops             x86_64         2.1.11-22.el7_1         @rhel-server-7                 37 k
 abrt-addon-pstoreoops             x86_64         2.1.11-22.el7_1         @rhel-server-7                 14 k
 abrt-addon-python                 x86_64         2.1.11-22.el7_1         @rhel-server-7                 30 k
 abrt-addon-vmcore                 x86_64         2.1.11-22.el7_1         @rhel-server-7                 41 k
 abrt-addon-xorg                   x86_64         2.1.11-22.el7_1         @rhel-server-7                 17 k
 abrt-cli                          x86_64         2.1.11-22.el7_1         @rhel-server-7                0.0
 abrt-console-notification         x86_64         2.1.11-22.el7_1         @rhel-server-7                1.3 k
 abrt-python                       x86_64         2.1.11-22.el7_1         @rhel-server-7                 56 k
 abrt-tui                          x86_64         2.1.11-22.el7_1         @rhel-server-7                 24 k
 docker-python                     x86_64         1.4.0-108.el7           @rhel-server-extras-7         176 k
 python-requests                   noarch         2.6.0-1.el7_1           @rhel-server-7                343 k
 python-urllib3                    noarch         1.10.2-2.el7_1          @rhel-server-7                369 k
 sos                               noarch         3.2-15.el7_1.5          @rhel-server-7                1.0 M

Transaction Summary
=====================================================================================================================
Remove  1 Package (+15 Dependent packages)

The Workaround

But here’s the workaround to get Ansible with Docker up & running is the following procedure:

  • remove the OS python-docker package
  • install the official PyPi docker-py package version 1.2.3 via pip
  • upgrade the six package to version >= 1.4.0 via pip without removing the OS package

So let’s update our playbook to meet the new requirements:

---
- hosts: docker.confirm.ch
  tasks:

    - name: make sure docker-python RPM is not installed
      yum:
        name: docker-python
        state: absent

    - name: make sure required PyPi packages are installed
      pip:
        name: '{{ item }}'
        state: present
      with_items: 
        - docker-py==1.2.3
        - six>=1.4.0

    - name: run hello-world docker container
      docker:
        name: hello-world
        image: hello-world
        state: present
  sudo: yes

Though there are some drawbacks. OS packages with dependencies to six (e.g. sosabrtmight not be tested against a newer version of it.

To look on the bright side, there’s already an official docker-py commit which requires six>=1.4.0. So in the end it’s just a matter of time until Red Hat will fix this. Hopefully we don’t have to wait another 2 years 😉

4 Comments

  • thomas Reply

    also make sure pip is installed (only with Python 2.7.9 and later)

    – name: make sure pip is installed
    easy_install:
    name: pip

    • Dominique Barton Reply

      Yep you’re right. Use `easy_install` like in your example above or `yum` to install pip:


      - name: make sure pip is installed
      yum:
      name: python-pip
      state: present

  • Daryn Hanright Reply

    Hi

    Just wondering what version of ansible you were using for this guide? Have followed it with ansible 1.8.2 & I still get the “NameError: global name ‘DEFAULT_DOCKER_API_VERSION’ is not defined”

  • Dominique Barton Reply

    Hi.

    Hmm strange.

    I think it was version `1.9.2` or `1.9.3`. However, we no longer use Ansible’s `docker` module because it was a bit of a hazzle, as you might already experienced 😉 Instead of it we’re using the `template` module to create a Docker Compose file and then run `docker-compose up -d` or whatever 🙂

    This works much better and out of the box (at least if you make sure Docker Compose is installed in advance).

    Cheers
    Domi

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