Open Stack

On Dec 5, 2013, at 12:42 PM, Andrew Plunk <andrew.plunk at RACKSPACE.COM> wrote:

>> Excerpts from Randall Burt's message of 2013-12-05 09:05:44 -0800:
>>> On Dec 5, 2013, at 10:10 AM, Clint Byrum <clint at fewbar.com>
>>> wrote:
>>> 
>>>> Excerpts from Monty Taylor's message of 2013-12-04 17:54:45 -0800:
>>>>> Why not just use glance?
>>>>> 
>>>> 
>>>> I've asked that question a few times, and I think I can collate the
>>>> responses I've received below. I think enhancing glance to do these
>>>> things is on the table:
>>>> 
>>>> 1. Glance is for big blobs of data not tiny templates.
>>>> 2. Versioning of a single resource is desired.
>>>> 3. Tagging/classifying/listing/sorting
>>>> 4. Glance is designed to expose the uploaded blobs to nova, not users
>>>> 
>>>> My responses:
>>>> 
>>>> 1: Irrelevant. Smaller things will fit in it just fine.
>>> 
>>> Fitting is one thing, optimizations around particular assumptions about the size of data and the frequency of reads/writes might be an issue, but I admit to ignorance about those details in Glance.
>>> 
>> 
>> Optimizations can be improved for various use cases. The design, however,
>> has no assumptions that I know about that would invalidate storing blobs
>> of yaml/json vs. blobs of kernel/qcow2/raw image.
> 
> I think we are getting out into the weeds a little bit here. It is important to think about these apis in terms of what they actually do, before the decision of combining them or not can be made.
> 
> I think of HeatR as a template storage service, it provides extra data and operations on templates. HeatR should not care about how those templates are stored.
> Glance is an image storage service, it provides extra data and operations on images (not blobs), and it happens to use swift as a backend.

This is not completely correct. Glance already supports something akin to templates. You can create an "image" with metadata properties that specifies a complex block device mapping which would allow for multiple volumes and images to connected to the vm at boot time. This is functionally a template for a single vm.

Glance is pretty useless if is just an "image storage" service, we already have other places that can store bits (swift, cinder). It is much more valuable as a searchable repository of bootable templates. I don't see any reason why this idea couldn't be extended to include more complex templates that could include more than one vm.

We have discussed the future of glance a number of times, and if it is really just there to serve up blobs of data + metadata about images, it should go away. Glance should offer something more like the AWS image search console. And this could clearly support more than just images, you should be able to search for and launch more complicated templates as well.

> 
> If HeatR and Glance were combined, it would result in taking two very different types of data (template metadata vs image metadata) and mashing them into one service. How would adding the complexity of HeatR benefit Glance, when they are dealing with conceptually two very different types of data? For instance, should a template ever care about the field "minRam" that is stored with an image?


I don't see these as significantly different types of metadata. Metadata for heat templates might be a bit more broad (minFlavor?) I would think that a template would care about constraints like this, especially when you consider that a user might want to give a command to launch a template but then override certain characteristics.

Vish

> Combining them adds a huge development complexity with a very small operations payoff, and so Openstack is already so operationally complex that HeatR as a separate service would be knowledgeable. Only clients of Heat will ever care about data and operations on templates, so I move that HeatR becomes it's own service, or becomes part of Heat.
> 
> 
> 
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