Development Quickstart¶
This page describes how to setup and use a working Python development environment that can be used in developing nova on Ubuntu, Fedora or macOS. These instructions assume you’re already familiar with git.
Following these instructions will allow you to build the documentation and run the nova unit tests. If you want to be able to run nova (i.e., launch VM instances), you will also need to — either manually or by letting DevStack do it for you — install libvirt and at least one of the supported hypervisors indicated in Feature Support Matrix. Running nova is currently only supported on Linux, although you can run the unit tests on macOS
Note
For how to contribute to Nova, see HowToContribute. Nova uses the Gerrit code review system, GerritWorkflow.
Setup¶
There are two ways to create a development environment: using DevStack, or explicitly installing and cloning just what you need.
Using DevStack¶
See Devstack Documentation. This should be done in a VM or other throwaway environment and not on your local host.
Once DevStack is deployed, you can connect to the environment and navigate to
the Nova repo (typically found at /opt/stack/nova).
Using your local host¶
DevStack installs a complete OpenStack environment. Alternatively, you can explicitly install and clone just what you need for Nova development. This will give you an environment suitable for running the Nova unit and functional tests, and for building documentation.
To begin, first grab the code from git:
git clone https://opendev.org/openstack/nova
cd nova
Then install the required tools and system dependencies. The process to do this varies depending on your host OS. Following are instructions on how to do this on Linux and on macOS.
Linux Systems
Install the prerequisite packages listed in the bindep.txt file.
On Debian-based distributions (e.g., Debian/Mint/Ubuntu):
sudo apt-get install python-pip tox
tox -e bindep
sudo apt-get install <indicated missing package names>
On Fedora-based distributions (e.g., Fedora/RHEL/CentOS Stream):
sudo dnf install python3-pip tox
tox -e bindep
sudo dnf install <indicated missing package names>
macOS Systems
Homebrew is very useful for installing dependencies. As a minimum for running tests, install the following:
brew install python3 tox
Note
Nova currently requires tox 4.x (the exact version is specified in [tox]
min_version in tox.ini). Ubuntu 24.04, Fedora 43, and Brew all
provide suitably new versions and tox has the ability to bootstrap itself
if/when we bump this further. However, if you’re on a system where tox is
not packaged or is too old, you can also install it from PyPI.
Building the documentation¶
Install the prerequisite packages: graphviz
To do a full documentation build, issue the following command from the root directory of the repo.
tox -e docs
That will create a Python virtual environment, install the needed Python prerequisites in that environment, and build all the documentation in that environment.
Running unit and functional tests¶
See Running Python Unit Tests.
Note that some functional tests use a database. See the file
tools/test-setup.sh on how the databases are set up in the
OpenStack CI environment and replicate it in your test environment.
Using the pre-commit hook¶
Nova can make use of the pre-commit framework to allow running of some linters on each commit. This must be enabled locally to function:
$ pip install --user pre-commit
$ pre-commit install --allow-missing-config
As a reminder, the hooks are optional and you are not enforced to run them.
You can either not install pre-commit or skip the hooks once by using the
--no-verify flag on git commit.
Using fake computes for tests¶
The number of instances supported by fake computes is not limited by physical
constraints. It allows you to perform stress tests on a deployment with few
resources (typically a laptop). Take care to avoid using scheduler filters
that will limit the number of instances per compute, such as NumInstancesFilter.
Fake computes can also be used in multi hypervisor-type deployments in order to take advantage of fake and “real” computes during tests:
create many fake instances for stress tests
create some “real” instances for functional tests
Fake computes can be used for testing Nova itself but also applications on top of it.
