On 29/12/15 07:41 -0600, Sam Matzek wrote:
On Thu, Dec 24, 2015 at 7:49 AM, Mikhail Fedosin <mfedo...@mirantis.com> wrote:Hello, it's another topic about glance v2 adoption in Nova, but it's different from the others. I want to declare that there is a set of commits, that make Nova version agnostic and allow to work with both glance apis. The idea of the solution is to determine the current api version in the beginning and make appropriate requests after. (https://review.openstack.org/#/c/228578/, https://review.openstack.org/#/c/238309/, https://review.openstack.org/#/c/259097/)Indeed, it requires some additional (and painful) work, but now all tempest tests pass in Jenkins. Note: this thread is not about xenplugin, there is another topic, called 'Xenplugin + Glance_v2 = Hate' Here the main issues we faced and how we've solved them: 1. "changes-since" filter for image-list is not supported in v2 api. Steve Lewis made a great job and implemented a set of filters with comparison operators https://review.openstack.org/#/c/197388/. Filtering by 'changes-since' is completely similar to 'gte:updated_at'. 2. Filtering by custom properties must have prefix 'property-'. In v2 it's not required. 3. V2 states that all custom properties must be image attributes, but Nova assumes that they are included in 'properties' dictionary. It's fixed with glanceclient's method 'is_base_property(prop_name)', that returns False in case of custom property. 4. is_public=True/False is visibility="public"/"private" respectively. 5. Deleting custom image properties in Nova is performed with 'purge_props' flag. If it's set to True, then all prop names, that are not included in updated data, will be removed. In case of v2 we have to explicitly specify prop names in the list param 'remove_props'. To implement this behaviour, if 'purge_props' is set, we make additional 'get' request to determine the existing properties and put in 'remove_prop' list only those, that are not in updated_data. 6. My favourite: There is an ability to activate an empty image by just providing 'size = 0': https://review.openstack.org/#/c/9715/, in this case image will be a collection of metadata. Glance v2 doesn't support this "feature" and that's why we have to implement a very dirty workaround: * v2 requires, that disk_format and container-format must be set before the activation. if these params are not provided to 'create' method then we hardcode it to 'qcow2' and 'bare'. * we call 'upload' method with empty data (data = '') to activate image. Me (and the rest glance team) think that this image activation with zero-size is inconsistent and we won't implement it in v2. So, I'm going to ask if Nova really needs this feature and maybe it's possible to make it work without it.Nova uses this functionality when it creates snapshots of volume backed instances, that is, instances that only have Cinder volumes attached and do not have an ephemeral disk. In this case Nova API creates Cinder snapshots for the Cinder volumes and builds the block_device_mapping property with block devices that reference the Cinder snapshots. Nova activates this image with size=0 because this image does not have a disk and simply refers to the collection of Cinder snapshots that collectively comprise the binary image. Callers of Glance outside of Nova may also use the APIs to create "block device mapping" images as well that contain references to Cinder volumes to attach, blank volumes to create, snapshots to create volumes from, etc during the server creation. Not having the ability to create these images with V2 is a loss of function.
I disagree. Being able to activate empty images breaks the consistency of Glances API and I don't think it should be considered a feature but a bug. An active image is an image that can be used to *boot* a VM. If the image is empty, you simply can't do that. Note that pointing to a block device makes the image "non-empty" already. There's a spec merged[0] and code written[1] to allow for using cinder as backend for Glance. If there's a missing functionality for the mapping users require, I believe activating empty images is not the solution for it. [0] https://review.openstack.org/183363 [1] https://review.openstack.org/166414
The callers could supply 1 byte of junk data, like a space character, but that would result in a junk image being stored in Glance's default backing store for the image. It would also give the impression that a real disk image exists for the image in a backing store which could be fetched, which is incorrect. If I remember correctly Glance V2 lets you transition an image from queued to active state with size = 0 if the image is using an external backing store such as http. The store is then called to fetch the size. Would it be possible to allow Glance to consider images with size = 0 and the block_device_mapping property to be "externally sourced" and allow the transition?
In v2 you can create an image and then add a location for it (this should be enabled, of course). You can even use cinder locations since Kilo (or Havana?). Cheers, Flavio -- @flaper87 Flavio Percoco
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