Difference between revisions of "Scope Management"

Revision as of 23:34, 17 August 2008

What's in Scope?

In gCube, a resource may only be shared within one or more scopes. Outside these, the resource can neither be discovered nor used.

A Running Instance, in particular, may operate in different scopes at different times. For this to happen, clients must specify a scope when contacting the instance. Similarly, any state which the instance might create must retain the scope of the call which triggered the creation.

It is so that resources, WS-Resources, and calls are all scoped in gCube.

Modelling Scope

In gCube, there are three levels of scope: the Infrastructure, the Virtual Organisation (VO), and the Virtual Research Environment (VRE).

Scopes at different levels are strictly related: a VRE is always relative to a VO which is in turn always relative to some infrastructure. Informally, we say that the VRE is below the VO and that the infrastructure is above it.

We use expressions of the form /A/B/C to denote a VRE C below a VO B below an infrastructure A. Informally, /A/B/C may be thought of as the fully qualified name of C. More formally, we use the following grammar for scope expressions:

SCOPE : = = I | VO | VRE
I :== /NAME
VO :== I/NAME
VRE :== VO/NAME
NAME :== <a conventional label>

In gCF, scope expressions can be conveniently thought as serialisations of GCUBEScope objects. to be continued...

Scope Rules

The basic scope rule is the intuitive one: a resource in a given scope is also below it but not above it.

So, a resource in scope /A/B may be shared across all the VREs below B but in other VOs below A.

The semantics of specific scopes and resources, however, may restrict the applicability of the basic rule.

The first common exception is that a resource shared in an infrastructure is not immediately available below it. Rather, the resource must be explicitly joined' to a VO before it becomes available to all the VREs below it.

to be continued

We model scoping as a binary relationship between resource and scopes. We write R in S to denote a pair (R,S) of a resource R and a scope S in the scoping relationship.

Scoping is constrained by a number of scope rules. Scope rules are specific to resource types. A default rule, however, applies to all of them:

Let VRE range offer virtual research environments, R be a resource and VO virtual organisation.

DEF) if R is shared in a VOs then it is also shared in VREs below: R in VO => for each VRE in VO. VRE below R

For convenience, we write S1 below S2 to indicate that S1 and S2 denote the same scope or that S1 is directly or indirectly relative to S2. Similarly, we write S1 above S2 to indicate that S1 and S2 denote the same scope or that S2 is directly or indirectly relative S1.

• NB: The opposite does not always hold: depending on resource type, a resource may be shared in a VRE but not in the VO above.
• NB: Most definitely, a resource shared in a GI is not automatically shared in the VOs. For this to happen, the resource may have to explicitly join a VO.

Scoping Rules for gCube Hosting Nodes

Let GI range over gCube Infrastructures and GHN be a hosting node.

GHN1) GHN may only be shared in one infrastructure: exist GI. GHN in GI and (GHN in S => S below GI)

GHN2) if a GHN is shared in a scope is also shared above it: GHN in S => for each S' above S. GHN in S'

• NB: GHN2) proves that the converse of DEF) holds for GHNs: A GHN cannot be shared in VRE(VO) if it is not shared also in the VO(GI) above.

gCore implications:

• DEF) + GHN2) => model GHN scope as a list of one GI and zero or more VOs.
• on add, enforce GHN1) and retain only VO from VRE scopes (GCUBEHostingNode)
• on remove, prevent removal of GI if attempted (GCUBEHostingNode)
• on bootstrap, require configuration of single GI and allow zero ore more start VOs (GHNBuilder)

Scoping Rules for gCube Services

Let SV be a gCube Service.

SV1) if SV is shared in a scope it is also shared below it: SV in S => for each S' in S. R in S'

• NB: This extends DEF) to infrastructure-level scope make scoping simplest for services.

gCore implications: none special, scopes are immutable for services (i.e. for the ones already deployed).

Scoping Rules for Running Instances (RIs) of gCube services

Running instances are a first example of resource type for which scoping rules are further constrained by the scope of related resources. In fact, running instances relate to their services and the hosting nodes on which they are deployed.

Let SV(RI) and GHN(RI) denote, respectively, the service of a RI and the GHN on which the RI is deployed.

RI1) RI can only be shared where its GHN and service can: RI in S => GHN(RI) in S and SV(RI) in S

• NB: The opposite of RI1) does not hold: a RI is not necessarily shared wherever its GHN and its service are.

gCore implications:

• on add, enforce RI1) (ServiceContext)
• on startup,
  • generic service: subscribe consumer for GHN remove scope events only (ServiceContext) => remove all RI scopes contained in those removed from the GHN (consumer).
  • local service: subscribe consumer for GHN remove and add scope events (ServiceContext) => add new GHN scopes to RI (consumer).
• on bootstrap,
  • allow JNDI configuration of zero or more start scopes (RIBuilder)
  • static only : add all GHN scopes if no start scopes are available (RIBuilder). Prevent in dynamic bootstrap.

Scoping Rules for WS-Resource generated by Running Instances of gCube services

WS-Resources are anther example of resource type for which scoping rules are further constrained by the scope of related resources, in this case the running instance which generate them. Let WSR denote a WS-Resource and RI(WSR) the RI through which has generated WSR.

WSR1) WSR can only be shared where its RI can: WSR in S => RI(WSR) in S

• NB: The opposite of RI1 does not hold: a RI is not necessarily shared wherever its GHN and its service are.

gCore implications:

• on creation, enforce WSR1) (GCUBEHandler)
• on remove, remove from all WS-Resource which have been created by some stateful-port-type of the RI below the removed RI scope;
  • due to persistence, cannot be easily performed locally, use instead queries to the IS

Configuring scope (Static scope)

Static scope applies only for those resources that can be manually created by humans. For such gCube resources, a scope S can be statically (i.e. manually) configured and changed through their appropriate configuration files.

Static scope for gCube Hosting Nodes

A gHN is always manually deployed, therefore a static scope configuration is always needed. Such a configuration is expressed with two parameters in the $GLOBUS_LOCATION/config/GHNConfig.xml file.

• infrastructure reports the GI the gHN joins (and it can be one and only one, as for GHN1). In the following example, the gHN is configured to join the /gcube infrastructure:

 <environment
        name="infrastructure"
        value="gcube"
        type="java.lang.String"
        override="false" />

• startScope is a comma-separated list of VOs the gHN joins. These VOs has to be below the infrastructure (as for GHN2)), otherwise they are ignored. The list of VOs can be an empty list. In the following example, the gHN is configured to join both the /gcube/devsec and the /gcube/testing VO:

<environment
        name="startScopes"
        value="devsec,testing"
        type="java.lang.String"
        override="false" />

Static scope for gCube Services

A gCube service has always only a static scope, specified at service registration time in the Software Repository service.

Static scope for Running Instances (RIs) of gCube services

Static scope for RIs has a mean only for those that are manually deployed. A RI can be configured to join one or more VOs and/or VREs with a comma-separated list. Due to RI1), the VOs has to be a subset of the VOs to which the GHN(RI) is joined to and the VREs has to be below the VOs to which the GHN(RI) is joined to.

In order to specify the static scope of a RI, insert a startScopes parameter in the service context section of the JNDI's RI as follows:

<service name="gcube/common/vremanagement/Deployer">
	
	<environment 
		name="configDir" 
	 	value="@config.dir@" 
	 	type="java.lang.String"
	 	override="false" />
		 		 	
	<environment 
		name="securityManagerClass" 
	 	value="org.gcube.common.core.security.GCUBESimpleServiceSecurityManager" 
	 	type="java.lang.String"
	 	override="false" />
	 	
	<environment 
		name="startScopes" 
	 	value="devsec/EM,testing/test1" 
	 	type="java.lang.String"
	 	override="false" />

</service>

This parameter is optional: if it is not used, the RI is automatically configured by the gCore to join the VO(s) expressed in the startScopes parameter of the GHNConfig.xml.

gCube Calls & the gCube Handler

[coming soon]

Scope Managers

[coming soon]

The Client Perspective:Scopes & Stubs