Notes on the Physiology Paper by Ian Foster et al: http://www.globus.org/research/papers/ogsa.pdf
1. Globus Toolkit provides the framework for grid-based applications. Gloubus
toolkit (latest version
is known as GT3) is a community-based, open architecture, open source set
of services and software libraries
that support Grid and Grid Appilcations.
2. Toolkit addresses the issues of secuirty, information discovery, resource
management, data management, communication,
fault detection, and portability. (GRAM, MDS-2, GSI, etc.)
3. Webservices will be teh foundational entity for grid services. (See
SOAP, WSDL, WS-inspection, WSFL orchestration
etc.)
4. OGSA; Open Grid Services Architecture
1) Computing is increasingly concerned with the creation,
management, and application of dynamic ensembles of resources,
and services and people.
2) OGSA supports creation, maintenance
and application of ensembles of services.
3) Object-orientation to service-orientation
4) A service is a network-enables entity
that provides some capability: a sophiticated object, a standardized object
5) OGSA: Computational resources, storage
resources, networks, programs, databases, and the like are all represented
as services.
6) Interoperabilty is a critical problem:
handled by dividing it into two issues:
a. Definition of service interface
b. protocols to invoke service interface
7) Virtualization through WSDL
WSDL allows multiple bindings
of the same interface and optimized binding for local access.
Central to virtualization is
the ability to adapt OS functions at a specific site, explotation of native
capability.
Virtualization allows the composition
of services to form more sophisticated services.
8) Ability to virtualize and compose services depends
on more than the standard interface definition.
We also require standard semantics
for service interaction: for example error notification, lifecycle management.
This need is addressed by a well-defined
set of interfaces called Grid Service.
9) Grid Service: A web service with multiple interfaces:
address discovery, dynamic service creation, lifetime managment,
notification, and mangeability.
10) Transient services and a static set of persistent
services. Transient service to query againt a database, a datamining operation.
Persistent services: security, naming..
11) Standard interfaces: in WSDL terms these
are portTypes. See Table 1:
portType: GridService,
NotificationSource, NotificationSink, Registry, Factory, HandleMap
Read the operations in
the portType and the respective semnatics.
12) Discovery:
Problem: Applications require
mechanisms for discovering available services and for determining the characteristics
of the services
to configure themselves
and their request.
Solution:
-- a standard representation of service data: information about
Grid Service instances which are structured as a set of named
and types XML elements
called service data elements.
--
A standard operation FindServiceData (pull) NotificationSource (push)
--
standard interface for registering information about Grid Service instances
with Registry services
13) Dynamic service creation
14) Lifetime management
15) Nitification: A collection of dynamic, distributed
servcies must be able to notify each other asynchronously of interesting
chnages
to their state. NotificationSource,
NotificationSink
16) OGSA defines the semantics of a Grid
service intsance: How it is created, how it is named, how its lifetime is
determined, how to communicate
with it.
17) Hosting environment addresses
the programming model, programming language, implementation tools, and execution
environment. It also defines
various development
and debuggng tools.
18) Host environment:
-- Interface
to the host environment consists of a registry, one or more factories, and
a handlemap service.
-- Each factory is registered in the registry, to enable clients to discover
available factroies.
-- when a factory receives a client request to create a Grid Servcie instance,
the factory creates a new instance, assigns it a handle, registers the instance
with the registry, maps the handle available to the handleMap service. HandleMap
maps handles to references, which may be local or remote.
19) Container/component (J2EE,
.NET, WebSphere, Sun One) hosting environments offer superios programmability,
manageability , flexibilty and safety.
These are prefereed over native
hosting environments.
20) Building Virtual Organization
Structures:
-- Simple hosting environment: located within a single administrative
domain.
---- contians one regsitry, several factories, and a HandleMap
---- each factory is registered in the Registry to allow client clients
to discover the factories.
---- client discovers a Factory using the Registry and then requests an
instance of a service..... similar what we discussed in item 18)
---- only difference is that HandlMap maps the handles to local references.
-- Virtual Hosting Envronement:
---- resources associated with a VO span heterogeneous, geographically distributed
hosting environments.
---- however the user inetrface is same.
---- There is highe level Registry which knows about lower level registries
and higher level factories that delegate greation requests to lower level
factories, clients interact directly with service instances.
-- Collective services
---- offer sophisticated virtual, collective, end-to-end services.
---- muliple lower level servcies are created and composed into a single
higher level service, which is exposed to the client.
21) Application example: p.17
and 18 (Figure 3) Lets go through the details.
22) OGSA Technical details
1. Service model: computation
resources, storage resources, networks, programs, databases etc. are all services.
This adoption
of a uniform service model means that all components of the environment are
virtual.
2. Everything
is a Grid Service: a Web service that conforms to a set of conventions and
supports standard interfaces for such
purposes
as lifetime management and security.
3. WS: portType -->
WSDL
GS:
serviceType --> extensible WSDL (GWSDL) portType+ additional information
.. versioning etc.
4. Protocol binding associted
with the service can define delivery semantics, for example addressing reliability.
5. Grid
Service is dynamic (can be created and destroyed dynamically) and stateful
(state corresponds to the instance).
6. Globally unique name
for a Grid service instance is Grid Service Handle (GSH). GSH has not
protocol or instance specific
information.
7. GSR: Grid Service
Reference is a instance specific information, GSR for Grid service may
change over its lifetime. Has an explicit
expiration
time.
8. Creating transient
services: Corresonding a transient service there is a factory service
that implements a Factory interface.
The Factory
interface's CreateService operation creates a requested Grid service and returns
the GSH and inital GSR for the
new service
instance.
9. Lifetime Management
10. Managing Handles and
References: (i) identifying the Handlemap service (ii) contacting the handleMap
to obtain the desired GSR.
11. Service Data and Service
Discovery:
-- associated
with Grid service is a set of service data, a collection of XML elements.
These are service data elements. A service data
element includes details such as a type, time to live, etc.
--- FindServiceData
can eb used to query and get the serviceData.
-- other service
data elements include GSH, GSR, primary key, home handleMap.
12. Notification: notification
framework allows clients to register interest in being notified of particular
messages and supports
asynchronous,
one way delivery of such notifications.
13. change management
23) Protocol bindings: reliable transport etc.
24) High level services: GRAM, GridFtp etc.