Open Stack

I'd like to clarify something.

On 9/25/15, 12:16 PM, "Mark Voelker" <mvoelker at vmware.com> wrote:
[big snip]
>Also worth pointing out here: when we talk about ³doing the same thing²
>from a DefCore perspective, we¹re essentially talking about what¹s
>exposed to the end user, not how that¹s implemented in OpenStack¹s source
>code.  So from an end user¹s perspective:
>
>If I call nova image-create, I get an image in my cloud.  If I call the
>Glance v2 API to create an image, I also get an image in my cloud.  I
>neither see nor care that Nova is actually talking to Glance in the
>background, because if I¹m writing code that uses the OpenStack API¹s, I
>need to pick which one of those two API¹s to make my code call upon to
>put an image in my cloud.  Or, in the worst case, I have to write a bunch
>of if/else loops into my code because some clouds I want to use only
>allow one way and some allow only the other.

The above is a bit inaccurate.

The nova image-create command does give you an image in your cloud.  The
image you get, however, is a snapshot of an instance that has been
previously created in Nova.  If you don't have an instance, you cannot
create an image via that command.  There is no provision in the Compute
(Nova) API to allow you to create an image out of bits that you supply.

The Image (Glance) APIs (both v1 and v2) allow you to supply the bits and
register them as an image which you can then use to boot instances from by
using the Compute API.  But note that if all you have available is the
Images API, you cannot create an image of one of your instances.

>So from that end-user perspective, the Nova image-create API indeed does
>³do the same thing" as the Glance API.

They don't "do the same thing".  Even if you have full access to the
Images v1 or v2 API, you will still have to use the Compute (Nova) API to
create an image of an instance, which is by far the largest use-case for
image creation.  You can't do it through Glance, because Glance doesn't
know anything about instances.  Nova has to know about Glance, because it
needs to fetch images for instance creation, and store images for
on-demand images of instances.


>At Your Service,
>
>Mark T. Voelker

Glad to be of service, too,
brian