[glue-wg] Who publishes UserDomains?

[Paul Millar]

Hi all,

Here's a potentially tricky question:  who publishes the UserDomain objects?

Consider an SE agent wishes to publish the "ownership" of the StorageShare 
objects.  To do this it should publish MappingPolicy objects, each of which 
will need to know (MappingPolicy: UserDomain.ID link-end 1..*).  To get these 
UserDomain.IDs the agent has two possibilities.  Either:

1. The SE publishing agent creates its own set of UserDomain objects; given 
this, it knows the UserDomain.ID

2. The SE queries for existing UserDomain objects for ones matching its 
requirements, so discovering the appropriate ID


Problems with solution 1.
---

Some client queries become (unnecessarily?) complex unless some form of 
merging takes place.  How does a client know which set of UserDomain objects 
is really the VO "ATLAS"?

One possible approach would be to merge the UserDomain objects that represent 
the same end-user-group (e.g., the same VO).  Unfortunately, this would 
likely be a fragile and incomplete process with the current set of 
attributes.  Clients that want to query against resources for some VO (e.g., 
ATLAS) would have to support querying against multiple UserDomain objects.


Problems with solution 2.
---

How should an agent discover which UserDomain object to use?  There's no 
attribute(s) useful for identifying a VO (or group within that VO) from 
characteristics; for example, publishing a VOMS prefix.

What should the publisher do for end-user groups that don't currently exists?  
If it publishes a (minimal) UserDomain object itself, then there's a 
potential race-conditions with multiple UserDomain objects being published.

Requiring some information to exist before publishing primary data will make 
the publishing process fragile.  For example:
	Temporary outages will have a knock-on effect: the info-service would be
	as reliable as each of the UserDomain publishing agents and the network
	links from these to all other grid components.

	If data is cached (local to the agent) is used to improve reliability, it's
	possible for publishers to use outdated information, so providing
	useless information, potentially affecting that VO's usage of the resource.

Which agents are responsible for publishing VO UserDomain information?  Would 
this be another centralised component and another barrier to forming a new 
VO?

What do others think?

Cheers,

Paul.