the anatomy and physiology of the grid revisited
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The Anatomy and Physiology of the Grid Revisited. Nenad Medvidovic USC-CSSE and Computer Science Department University of Southern California [email protected] http:// / Collaborative work with Joshua Garcia, Ivo Krka , Chris Mattmann , and Daniel Popescu. What is the grid?.

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the anatomy and physiology of the grid revisited

The Anatomy and Physiologyof the Grid Revisited

Nenad MedvidovicUSC-CSSE and Computer Science DepartmentUniversity of Southern California

[email protected]

Collaborative work with Joshua Garcia, IvoKrka, Chris Mattmann, and Daniel Popescu

what is the grid
What is the grid?
  • A distributed systems technology that enables the sharing of resources across organizations scalably, efficiently, reliably, and securely
  • Analogous to the electric grid
why study the grid
Why Study the Grid?
  • A highly successful technology
  • Deficiencies in the existing guidance for building grids
    • More to come
  • Grids are not easy to build
    • See CERN’s Large Hadron Collider
  • Their architecture was published very early
    • “anatomy” and “physiology”
  • Yet “What is (not) a grid?” is still a subject of debate
the architectural perspective
The Architectural Perspective
  • Grids are large, complex systems
    • Thousands of nodes or more
    • Span many agency boundaries
  • Qualities of Service (QoS) are critical
    • Scalability
    • Security
    • Performance
    • Reliability ...
  • Software architecture is just what the doctor ordered
    • The set of principal design decisions about a software system [Taylor, Medvidovic, Dashofy 2009]
so what did we set out to do
So, What Did We Set out to Do?
  • Study grid’s reference requirements and architecture
  • Study the architectures of existing grid technologies
  • Compare the two
    • Knowing that there will likely be very few straightforward answers
  • Suggest how to fix any discrepancies
    • Knowing that there will likely be very few straightforward answers
architecture recovery technique focus
Architecture Recovery Technique- Focus -
  • Establish idealized architecture and candidate architectural style(s)
  • Identify data and processing components
    • Groups implementation modules according to a set of rules
  • Map identified data and processing components onto an idealized architecture
  • Examine
    • Source code
    • Documentation
    • Runtime behavior
    • Tie to requirements satisfied by component
rules of focus
Rules of Focus
  • Group based on isolated classes
  • Group based on generalization
  • Group based on aggregation
  • Group based on composition
  • Group based on two-way association
  • Identify domain classes
  • Merge classes with a single originating domain class association into domain class
  • Group classes along a domain class circular dependency path
  • Group classes along a path with a start node and end node thatreference a domain class
  • Group classes along paths with the same end node, and whose start node references the same domain class
some refinements to the rules
Some Refinements to the Rules
  • Domain class rules
    • Class with large majority of outgoing calls
  • Exclusion rules
    • Class with large majority of incoming calls
    • Utility classes
    • Heavily passed data-structures
    • Benchmarking and test classes
  • Additional groupings
    • By exception
    • By interface
    • By package if idealized architecture matches first-class component
focus rules for distributed systems
Focus Rules for Distributed Systems
  • Infer distributor connectors from idealized architecture
  • Classes with methods and names similar to first-class components are domain classes
  • Classes importing network communication libraries are domain classes
  • main() functions often identify first-class components
  • Classes deployed onto different hosts must be grouped separately
discovered discrepancies
Discovered discrepancies
  • Empty layers
  • Skipped Layers
  • Up-calls
  • Multi-layer components
what about globus1
Two layer boundary AND



Couldn’t determine right “layer”


Two layer boundary AND



Two layer boundary AND


What about Globus?
revised grid architecture
Revised Grid Architecture
  • The connectivity layer is eliminated
  • Explicitly addressing deployment view
  • Subsystem types rather than layer-oriented
  • Four architectural styles comprise the grid
    • Client/server
    • Peer-to-peer
    • Layered
    • Event-based
  • An improved classification of grid technologies
grid styles c s
Grid Styles – C/S
  • Applicationcomponents are clients to Collectivecomponents
    • e.g., application components query for resource component locations from collective components
  • Applicationcomponents are clients to Resourcecomponents
    • e.g., direct job submission from application components to resource components
  • Resourcecomponents can act as clients to Collectivecomponents
    • e.g., resource components may obtain locations of other resource components through collective components
grid styles p2p
Grid Styles – p2p
  • Resource componentsare peers
    • e.g., Grid Datafarm Filesystem Daemon (gfsd) instance makes requests for file data from other gfsds
  • Collective components are peers
    • e.g., iRODS agents communicate with each other to exchange data to create replicas
grid styles event based
Grid Styles – Event-Based
  • Resource components notify Collective components that monitor them
    • e.g., executors send heartbeats to managers
grid architectural styles layered
Grid Architectural Styles – Layered
  • Collective or Resource components request services from Fabric components
    • e.g., iRODS agent accesses a DBMS with metadata
grid technology classification
Grid Technology Classification
  • Computational grid
    • Implementing all Collective components
    • e.g., Alchemi and Sun Grid Engine
grid technology classification1
Grid Technology Classification
  • Data grid
    • Job scheduling components in Collective subsystem are not required
    • e.g., Grid Datafarm and Hadoop
grid technology classification2
Grid Technology Classification
  • Hybrid
    • Resource components providing services either to perform operations on a storage repository or to execute a job or task
    • e.g. Gridbus Broker and iRODS

Computational Resource

File Resource

correcting violations in the reference architecture
Correcting Violations in the Reference Architecture
  • Why were there originally so many upcalls?
    • Legitimate client-server and event-based communication
  • Why so many skipped layer calls?
    • The Fabric layer was at the wrong level of abstraction
    • Mostly utility classes that should be abstracted away
  • Why so many multi-layer components?
    • Connectivity layer was at the wrong level of abstraction
    • Not a layer, but utility libraries to enable connector functionality
    • Also accounts for skipped layer calls
  • Benefit of the deployment view
    • Essential for distributed systems
    • Helped to identify that the Fabric layer was not abstracted properly
where are we currently
Where Are We Currently?
  • There are remaining violations
    • Are they legitimate or a result of an improperly recast reference architecture?
  • Original Focus is not ideal for recovering systems of these types
    • Distributed systems realized by a middleware
  • A more automated approach that combines static and dynamic analysis would be preferable
  • Use the recast reference architecture to build a new grid
  • What are the overarching grid principles?
evolving grid principles
Evolving Grid Principles
  • A grid is a collection of logical resources (computing and data) distributed across a wide-area network of physical resources (hosts).
  • In a single grid-based application, the logical resources are owned by a single agency, while the physical resources are owned by multiple agencies.
  • All resources in a grid are described using a common meta-resource language.
  • Atomic-level logical resources are defined independently of the atomic-level physical resources.
  • The allocation of the atomic-level logical resources to the atomic-level physical resources can be N:M.
  • All computation in a grid is initiated by a client, which is a physical resource. The client sends the logical resources to the servers, which are also physical resources. A server can, in turn, delegate the requested computation to other physical resources.
  • All agencies that own physical resources in a grid must be able to specify policies that enforce the manner in and extent to which their physical resources can be used in grid applications.