Download Designing Distributed Applications with Mobile Code Paradigms

Designing
Distributed Applications with
Mobile Code Paradigms
Antonio Carzaniga
Gian Pietro Picco
Giovanni Vigna
Politecnico di Milano
Politecnico di Torino
Politecnico di Milano
http://www.elet.polimi.it/~carzaniga
http://www.polito.it/~picco
http://www.elet.polimi.it/~vigna
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Internet
• The largest distributed system ever built
• Communication infrastructure is evolving
at a fast pace
• Computational infrastructure is primitive and
characterized by slow evolution
• A new research effort: distributed applications in
an Internet scale
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A World-Wide
Middleware
•
•
•
•
Hides components’ location
Provides homogeneous access primitives
Supports client-server computing paradigm
Main problem:
– Local and remote interaction have different semantics
in terms of latency, access to memory, partial failure
and concurrency
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Mobile Code
Technology
• Location is a pervasive abstraction
– Local interaction is different from remote interaction
– Local interaction is less expensive
• Applications can dynamically change
– the code they are executing
– their location
• Strongly and weakly mobile systems
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From Technology to
Design Paradigms
• Abstract away from mobile code technology
• Location, and mobility of both code and
components should be taken into account at the
design level
• “Architectural styles” that employ some form of
code mobility
– Code On Demand
– Remote Evaluation
– Mobile Agent
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Architectural
Abstractions
• Components
– Resource components (Data, devices, code)
– Computational components
X
• Execution state
• Private data
• Bindings to other components (e.g., code)
• Interactions
• Sites
– Support execution
– Support cheap interaction
Site Y
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Mobile Code
Design Paradigms
• Interaction patterns that define the coordination and
relocation of components needed to perform a service
• Service can be carried out when:
– resources
– know-how
– computational component responsible for execution
are at the same location
X
Site Y
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A chocolate cake
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Client-Server
PLEASE, MAKE ME
A CHOCOLATE CAKE
A
Request
B
Reply
Site A
Site B
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Remote Evaluation
PLEASE, MAKE ME A
CHOCOLATE CAKE.
HERE IS THE RECIPE:
TAKE TWO EGGS...
A
Request
B
Reply
Site A
Site B
10
Code On Demand
PLEASE, TELL
ME THE RECIPE
A
Request
B
Reply
Site A
Site B
11
Mobile Agent
HERE I AM!
CAN I USE YOUR
OVEN?
A
Site A
Move
Site B
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Why to Use
Code Mobility?
• Deployment and upgrade of distributed
applications
• Customization of services
• Support for disconnected operations
• Improved fault tolerance
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How to Use
Code Mobility?
• There is no “universally best” paradigm: clientserver may still be the right answer
• Trade-offs have to be analyzed on a case-by-case
basis
• How to evaluate the best solution?
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A Data Mining
Example
• It is often claimed that data mining is the “perfect”
application for code mobility
• Evaluation of three different architectures
– Goal: to optimize network traffic
– Identification of the relevant parameters
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Client-Server
r
h
r
b
avg. # of docs.
per node
request
size
avg. size of
a doc. body
TCS = (Dr + iDr + Dh + iDb) N
network
traffic
density of
relevant info
avg. size of
a doc. header
number of
nodes
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Remote Evaluation
CREV
r
iDb
request
size
avg. # of docs
per node
avg. size of
a doc. body
TREV = ((r + CREV+ iDb) N
network
traffic
size of
code sent density of
relevant info
number of
nodes
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Mobile Agent
state CMA
request
size
density of
relevant info
r
avg. size of
a doc. body
TMA = (r + CMA + s + ½iDbN) (N+1)
network
traffic
size of
code sent
size of
“internal”state
avg. # of
docs per node
number of
nodes
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Findings
• Traffic Overhead: O = T - iDbN
OCS = (r + ir + h)DN
OREV = (r + CREV)N
OMA = (r + CMA + s)(N+1) + ½(N-1)I
• MA is the worst (at least in this example and as far as
network traffic is concerned)
• Trade-off between CS and REV:
If r << CREV (r + ir + h) D > CREV
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Conclusions
• Mobile code languages support new design
paradigms for developing distributed applications
• Characterization of the paradigms
• Case-by-case evaluation of tradeoffs
20
Parallel and Future
Work
• Evaluation of the independence of the paradigms
from the technology
• Formalization of the paradigms
• Application to a real application domain
(network management)
• Implementation of technology directly supporting
the paradigms
• Security issues
21
Acknowledgments
Artwork by Maria Grazia Galliani
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