Open Stack

On Sep 25, 2015, at 1:24 PM, Brian Rosmaita <brian.rosmaita at RACKSPACE.COM> wrote:
> 
> 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.

Yup, that’s fair: this was a bad example to pick (need moar coffee I guess).  Let’s use image-list instead. =)

At Your Service,

Mark T. Voelker


> 
> 
>> At Your Service,
>> 
>> Mark T. Voelker
> 
> Glad to be of service, too,
> brian
> 
> 
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