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 an 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).

Guideline to include your requirement in the requirements.txt file

As described above, we do not include all the possible requirements needed by glance features in the source tree requirements file. Therefore, when you decide to use an advanced feature in glance, you have to check the documentation/guidelines for those features to set up the feature in a workable way. To reduce pain, the development team works with different operators to figure out when a popular feature should have its dependencies included in the requirements file. However, there is 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. Propose a change against the openstack/requirements project to include the requirement(s) as a part of the global-requirements and upper-constraints files.
  2. If your requirement is not a part of the project, propose a change adding that requirement to the requirements.txt file in glance. Include a Depends-On: <ChangeID> flag in the commit message, where the ChangeID is the gerrit ID of corresponding change against openstack/requirements project.

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.

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