Zero-byte image snapshot leads to error launching an instance from snapshot

[Luo Gangyi]

When I try to launch an instance of snapshot image (which was a snapshot of a volume-backed instance), the 'launch button' has no response.

How to reproduce:
1. Launch an instance by using "boot from image(create new volume)"
2. Take a snapshot of this instance, this operation will produce a image which size is 0 byte.
3. Launch an instance by using the image generated in step 2, the 'launch button' has no response.

If I open the console of web browser, I can see the Error Message
 "An invalid form control with name='volume_size' is not focusable. "

[Gary W. Smith (gary-w-smith)]

Cinder seems to be reporting the size of the volume correctly (1GB). If you attempt to launch in image from that volume via the Project -> Compute -> Volumes page, it works correctly.

But on the instances page, nova is reporting the size to be 0 bytes; also evidenced by nova image-show giving OS-EXT-IMG-SIZE:size of 0. So indications point to a bug in nova at this point. Will update with additional findings.

[Gary W. Smith (gary-w-smith)]

It seems to me that even if it is a bug in nova, that the Launch action should be disallowed in the images page if the size is 0, since it will lead down into this rathole for the user.

[Gary W. Smith (gary-w-smith)]

Note that glance, whose client is responsible for querying the data for the launch instance dialog, is also returning 0 for the size

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/125479

[Gary W. Smith (gary-w-smith)]

Per the discussion in gerrit, the zero-byte snapshot is normal from nova/glance, as it reflects that fact that no space is being taken in glance, since the volume snapshots are stored in cinder.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/125479
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=63a5ad95f581354abf60c67a9f865041f5d5e05f
Submitter: Jenkins
Branch: master

commit 63a5ad95f581354abf60c67a9f865041f5d5e05f
Author: Gary W. Smith <email address hidden>
Date: Wed Oct 1 16:48:49 2014 -0700

    Enable launching instance from zero-size image snapshot

    Remove the general hardcoded minimum of 1GB volume size on the create
    instance workflow, and selectively enforce it when the volume size field
    is used and editable: namely, when launching an instance from an image
    and creating a new volume.

    This general minimum was preventing the launch of instances from image
    snapshots (whose size is reported as 0) by causing browser errors as the
    browser tried to highlight the error of the invisible size field.

    Closes-Bug: 1374931
    Change-Id: Ied0eb41f5198d935bbb0896e5004ea78176bc2b8