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. GT4 will be released soon.
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 the 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.
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 no 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.