Aug 12, 2016

Document Binary Package Dependencies - not only for OpenStack Python Packages

Python developers record their dependencies on other Python packages in requirements.txt and test-requirements.txt. But some packages havedependencies outside of python and we should document thesedependencies as well so that operators, developers, and CI systems
know what needs to be available for their programs.

Bindep is a solution to this, it allows a repo to document binarydependencies in a single file. It even enablies specification of which distribution the package belongs to - Debian, Fedora, Gentoo, openSUSE, RHEL, SLES and Ubuntu have different package names - and allows profiles, like a test profile.

Bindep is one of the tools the OpenStack Infrastructure team has written and maintains. It is in use by already over 130 repositories.

For better bindep adoption, in the just released bindep 2.1.0 we have changed the name of the default file used by bindep from other-requirements.txt to bindep.txt and have pushed changes to master branches of repositories for this.

Projects are encouraged to create their own bindep files. Besides documenting what is required, it also gives a speedup in running tests since you install only what you need and not all packages that some other project might need and are installed  by default. Each test system comes with a basic installation and then we either add the repo defined package list or the large default list.

In the OpenStack CI infrastructure, we use the "test" profile for installation of packages. This allows projects to document their run time dependencies - the default packages - and the additional packages needed for testing.

Be aware that bindep is not used by devstack based tests, those have their own way to document dependencies.

A side effect is that your tests run faster, since they have less packages to install. A Ubuntu Xenial test node installs 140 packages and that can take between 2 and 5 minutes. With a smaller bindep file, this can change.

Let's look at the log file for a normal installation with using the default dependencies:
2 upgraded, 139 newly installed, 0 to remove and 41 not upgraded
Need to get 148 MB of archives.
After this operation, 665 MB of additional disk space will be used.

Compare this with the openstack-manuals repostiry that uses bindep - this example was 20 seconds and not minutes:
0 upgraded, 17 newly installed, 0 to remove and 43 not upgraded.
Need to get 35.8 MB of archives.
After this operation, 128 MB of additional disk space will be used.

If you want to learn more about bindep, read the Infra Manual on package requirements 
If you have questions about bindep, feel free to ask the Infra team on #openstack-infra.
Thanks to Anita for reviewing and improving this blog post and to the OpenStack Infra team that maintains bindep, especially to Jeremy Stanley and Robert Collins.