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).

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.

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