Running Glance on Windows¶
The goal is to allow Glance services to run on Windows, which enables Hyper-V OpenStack deployments to take full advantage of Microsoft storage solutions.
At the moment, Glance services cannot be run on Windows. To bring some context, there are OpenStack deployments that rely on Hyper-V compute nodes along with other Microsoft technologies.
In terms of storage, the most commonly used SDS solution is Storage Spaces Direct (S2D) along with highly available Scale-Out File Server (SoFS) SMB shares.
One issue is that the Linux cifs driver currently provides limited HA SMB share support (most versions can’t even connect to HA shares, there’s no Witness service support, automatic failover was recently added).
That being considered, most deployers have to use a separate storage backend for their Glance images (e.g. Swift, Ceph, etc).
Allowing Glance to run on Windows will allow deployers to benefit more from their S2D backends, commonly used for storing VM disks (currently handled by Nova as root images or Cinder as attachable volumes). In particular, this will be useful for hyper-converged deployments, where having to deploy yet another storage backend may not be desired.
Getting Glance services to run on Windows is not that difficult. There are just a few things that we need to change:
avoid forking, not available on Windows
avoid unavailable signals
avoid renaming/deleting in-use files
avoid using binaries that aren’t available on Windows
avoid having eventlet monkey-patch the os module as this will cause subprocess.Popen to fail
avoid missing features or libraires (e.g. xattr)
some small differences in path handling (‘/’ will be handled as a relative path)
avoid connecting to ‘0.0.0.0’, use ‘127.0.0.1’ instead. This mostly applies to the functional tests
All the above points are covered in less than 150 LOC (a few hundred more if we count the tests as well), without affecting the Linux behavior.
os-win library will be used for most of the Windows low-level
operations, which is an official OpenStack project.
The main goal is to use the filesystem driver along with SMB shares or Cluster Shared Volumes (CSV).
IIS will not be supported initially, using eventlet wsgi instead (which happens to be the recommended way of deploying Glance at the moment).
For Hyper-V deployments, the alternative is to keep running Glance on separate Linux hosts, having to deploy an additional storage backend or go with the limited HA SMB share support that’s currently available on Linux.
Data model impact¶
REST API impact¶
Other end user impact¶
Performance wise, there shouldn’t be any big differences. Spinning up new processes may be a bit slower on Windows, for which reason the functional tests may take longer to complete.
Other deployer impact¶
Glance will now be able to run on Windows. Not much changes config wise.
Keep in mind that we’re mainly targeting the file store for the beginning (which is the main reason we want Glance to run on Windows).
Glance will prefferably run as a Windows service. In general, we provide MSI packages that simplify installing and configuring OpenStack services (e.g. Nova, Neutron agent, Cinder, etc), which can also be run unattendedly.
We intend to provide Juju charms as well that will allow deploying Glance on Windows.
One thing to note is that
os-win currently supports Windows Sever 2012 or
Developers should keep in mind that Glance is supposed to be portable.
Judging from past experience, this hasn’t been a problem with other OpenStack projects. Glance doesn’t use too many platform specific libraries or binaries, so it should be fine.
- Primary assignee:
- Other contributors:
This work has been divided in 3 patches:
a small patch that allows Glance services to run on Windows
an additional one that allows multiple processes to be used by API services
a patch that allows all Glance unit and functional tests to run on Windows
A few small changes were needed on
os-win as well, exposing some low-level
We rely on
os-win, which is an official OpenStack library that exposes
low-level Windows functionality. It’s currently used by a few other OpenStack
projects, such as Nova, Cinder, Ceilometer, networking-hyperv, etc.
The already existing tests provide enough coverage. Still, the unit and functional tests will need some small changes in order to be able to run on Windows (currently relying on some Linux specific functionality).
We intend to provide 3rd party CI testing. For the record, we’re currently voting on Nova, Cinder and Neutron patches, running tests against Hyper-V.
The documentation should be updated to point out the fact that Glance is now Windows compatible, along with some installing and configuration guide.