Virtual Environments

Virtual Environments

Python virtual environments provide a mechanism for isolating python packages from the system site packages, and other virtual environments. Kolla-ansible largely avoids this problem by deploying services in Docker containers, however some python dependencies must be installed both on the Ansible control host and the target hosts.

Ansible Control Host

The kolla-ansible python package and its dependencies may be installed in a python virtual environment on the Ansible control host. For example:

virtualenv /path/to/venv
source /path/to/venv/bin/activate
pip install -U pip
pip install kolla-ansible

It may be advantageous to also install Ansible in the virtual environment.

source /path/to/venv/bin/activate
(venv) pip install ansible
(venv) deactivate

To use the virtual environment, it should first be activated:

source /path/to/venv/bin/activate
(venv) kolla-ansible --help

The virtual environment can be deactivated when necessary:

(venv) deactivate

Note that the use of a virtual environment on the Ansible control host does not imply that a virtual environment will be used for execution of Ansible modules on the target hosts.

Target Hosts

Ansible supports remote execution of modules in a python virtual environment via the ansible_python_interpreter variable. This may be configured to be the path to a python interpreter installed in a virtual environment. For example:

ansible_python_interpreter: /path/to/venv/bin/python

Note that ansible_python_interpreter cannot be templated.

Kolla-ansible provides support for creating a python virtual environment on the target hosts as part of the bootstrap-servers command. The path to the virtualenv is configured via the virtualenv variable, and access to site-packages is controlled via virtualenv_site_packages. Typically we will need to enable use of system site-packages from within this virtualenv, to support the use of modules such as yum, apt, and selinux, which are not available on PyPI.

When executing kolla-ansible commands other than bootstrap-servers, the variable ansible_python_interpreter should be set to the python interpreter installed in virtualenv.

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