External Requirements
Affecting Glance

Like other OpenStack projects, Glance uses some external libraries
for a subset of its features. Some examples include the
qemu-img utility used by the tasks feature,
sendfile to utilize the “zero-copy” way of copying data
faster, pydev to debug using popular IDEs,
python-xattr for Image Cache using “xattr” driver.

On the other hand, if dnspython is installed in the
environment, Glance provides a workaround to make it work with IPV6.

Additionally, some libraries like xattr are not
compatible when using Glance on Windows (see the documentation on config options
affecting the Image Cache <configuring>).

Guideline
to include your requirement in the requirements.txt file

As described above, we don’t include all the possible requirements
needed by Glance features in the source tree requirements file. So, when
an operator decides to use an advanced feature in
Glance, we ask them to check the documentation/guidelines for those
features to set up the feature in a workable way. In order to reduce the
operator pain, the development team likes to work with different
operators to figure out when a popular feature should have its
dependencies included in the requirements file. However, there’s a
tradeoff in including more of requirements in source tree as it becomes
more painful for packagers. So, it is a bit of a haggle among different
stakeholders and a judicious decision is taken by the project PTL or
release liaison to determine the outcome.

To simplify the identification of an advanced
feature in Glance we can think of it as something not being
used and deployed by most of the upstream/known community members.

To name a few features that have been identified as advanced:

• glance tasks
• image signing
• image prefetcher
• glance db purge utility
• image locations

Steps
to include your requirement in the requirements.txt file

1. First step is to propose a change against the
openstack/requirements project to include the
requirement(s) as a part of global-requirements and
upper-constraints files.

2. If your requirement is not a part of the project, you will have to
propose a change adding that requirement to the requirements.txt file in
Glance. Please include a Depends-On: <ChangeID> flag
in the commit message, where the ChangeID is the gerrit ID
of corresponding change against openstack/requirements
project.

3. A sync bot then syncs the global requirements into project
requirements on a regular basis, so any updates to the requirements are
synchronized on a timely basis.