[glue-wg] Extending GLUE 2.0 for Cloud services

[Paul Millar]

Hi Salvatore,

On 04/11/13 13:58, Salvatore Pinto wrote:
> The first proposed draft is attached. We would really appreciate your
> comments and maybe to add a point for discussion in the next WG meeting.

Thanks for posting the document.

I haven't really gone through it in detail, so these are just some 
initial observations.

First, it looks like you have inserted the word "Cloud" as a prefix to 
every class in the document.  This isn't an extension, but a complete 
rewrite!

Second, GLUE 2 contains extension points to allow communities to gain 
experience with new information without requiring the change of LDAP (or 
other) schemas on deployment machines.  If you haven't already got 
operational experience of the cloud extensions then you really should 
consider using these extension points first.

Third, some of the objects show no additional information beyond the 
existing GLUE 2.0 definitions; for example, the 
CloudStorageAccessProtocol seems identical (from memory) to the 
StorageAccessProtocol.

Fourth, the inheritance model seems broken.  Many classes show 
considerable overlap with their non-Cloud equivalents: 
CloudStorageServiceCapacity has TotalSize, FreeSize, etc, but also 
StoredObjects.  As the cloud versions do not extend from the non-Cloud 
classes, a publishing system would have to publish twice as many objects 
(the Cloud ones and the non-Cloud ones).

NB that inheritance isn't the solution to this problem; rather, you 
should have non-overlapping attributes.

Fifth, have you considered what is current state-of-art within the cloud 
ecosystem?  Talking specifically about storage, you should look at what 
already exists.  In particular, CDMI provides a standards-based 
interface for interacting with cloud storage.  It includes specific 
metadata about a storage system.  I suggest you look at this metadata as 
a source of inspiration.  NB. I'm NOT suggesting you copy all the 
metadata from CDMI into GLUE 2!

Finally, please be careful that any additional publishing fits in with 
existing storage systems.  Grid and cloud are not two mutually exclusive 
worlds; with dCache, for example, we have software where a single 
storage instance can provide both grid- and cloud-like storage.  It 
should be possible for such systems to publish themselves without 
doubling the number of objects.

HTH,

Paul.