Presentation given at TOOLS Europe 2011 in Zurich, on June 30, 2011. This work has been developed during my M.Sc. thesis in Politecnico di Milano.

1. Computational REST Meets Erlang
Alessandro Sivieri Gianpaolo Cugola Carlo Ghezzi
DeepSE Group
Dipartimento di Elettronica e Informazione
Politecnico di Milano
49th International Conference on
Objects, Models, Components and Patterns
June 30, 2011

2. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
1 Introduction
2 The CREST-Erlang architecture
3 A performance assessment
4 Conclusions
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 2/21

3. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Outline
1 Introduction
2 The CREST-Erlang architecture
3 A performance assessment
4 Conclusions
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 3/21

4. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
The scenario
Today’s applications
Large-scale and distributed on the Web
Components running on different devices
Services administered by different organizations
Long time executions, without interruptions or failures
We need frameworks able to
Support scalability and reliability
Guarantee isolation among components
Offer mechanisms for dynamic update of functionalities
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 4/21

5. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
REpresentational State Transfer
The model
Client-server separation for scalability and portability of the
code
Stateless communication for reliability
Caching mechanisms for scalability
The generic interface
Independence of applications on specific services
Application data must be encoded in a standard format
A host may not be able to correctly interpret these data
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 5/21

6. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
REpresentational State Transfer
The model
Client-server separation for scalability and portability of the
code
Stateless communication for reliability
Caching mechanisms for scalability
The generic interface
Independence of applications on specific services
Application data must be encoded in a standard format
A host may not be able to correctly interpret these data
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 5/21

7. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Computational REST
Designed as a response to real world problems
Adapts REST for an Internet of applications
From a Web of data to a Web of computations
Same REST principles, different key abstraction
Erenkrantz, J.R., Computational REST: a new model for decentralized,
Internet-scale applications, 2009
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 6/21

8. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Scheme
Proposed as the lingua franca for the Web
Functional language
Native support for continuations
History of uses for mobile code
Drawbacks
No native support for distributed applications
The need to develop many CREST-related concepts (light
processes, communication facilities . . . )
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 7/21

9. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Scheme
Proposed as the lingua franca for the Web
Functional language
Native support for continuations
History of uses for mobile code
Drawbacks
No native support for distributed applications
The need to develop many CREST-related concepts (light
processes, communication facilities . . . )
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 7/21

10. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Erlang
Erlang as the lingua franca for the Web
Fault-tolerance and “hot” code update
Distributed applications with an actor-like concurrency model
Design patterns (generic server, supervisor . . . )
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 8/21

11. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Outline
1 Introduction
2 The CREST-Erlang architecture
3 A performance assessment
4 Conclusions
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 9/21

12. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Overview
The main architecture
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 10/21

13. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
A service example
1 m y _ s e r v i c e ( S t a t e ) −>
2 receive
3 { Pid , [ {" p a r 1 " , P1} , . . . {" parN " , PN} ] } −>
4 % Do y o u r j o b a c c e s s i n g par1 , . . . parN
%
5 % e v e n t u a l l y c r e a t e a new s t a t e
%
6
7 % I f n e c e s s a r y , spawn m y s e l f on a h o s t
%
8 invoke_spawn ( Hostname , ?MODULE,
9 f u n ( ) −> m y _ s e r v i c e ( NewState )
end ) ,
10
11 % F i n i s h with a t a i l r e c u r s i o n
%
12 m y _ s e r v i c e ( NewState )
13 end .
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 11/21

14. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
So far so good
Full implementation of the Computational REST architectural
style
Erlang is the proposed language of choice for a Web of
computations
Minor development effort
CREST-Erlang prototype outperforms the CREST-Scheme one
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 12/21

15. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Security concerns
The problem
Mobile code may cause two kinds of problems:
Security of the host with respect to the code
Security of the code with respect to the host
Neither of these have found, as of today, a stable solution.
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 13/21

16. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
CREST security proposals
CREST-Scheme
JVM sandbox (implemented)
Bytecode inspection and self-certifying URLs (ideas)
CREST-Erlang
Trusted network: mutual authentication with SSL.
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 14/21

17. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
CREST security proposals
CREST-Scheme
JVM sandbox (implemented)
Bytecode inspection and self-certifying URLs (ideas)
CREST-Erlang
Trusted network: mutual authentication with SSL.
In both cases they are not enough.
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 14/21

18. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Outline
1 Introduction
2 The CREST-Erlang architecture
3 A performance assessment
4 Conclusions
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 15/21

19. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Implementation effort
Stateful and stateless services
Service composition
Framework Framework source code Demo source code
CREST-Scheme 5938 817
CREST-Erlang 2957 768
# of lines of code comparison
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 16/21

20. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Performances
CREST-Scheme demo performances
(a) Response time (b) Throughput
There is no caching mechanism.
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 17/21

21. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Performances
Test application performances
(a) Response time (b) Throughput
There is no caching mechanism.
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 17/21

22. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Outline
1 Introduction
2 The CREST-Erlang architecture
3 A performance assessment
4 Conclusions
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 18/21

23. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
CREST-Erlang
Erlang
Native support for
distribution
concurrency
fault-tolerance
The security problem
Computational REST
A possible evolution addressing the growing presence of
applications interfacing through the Web
Is HTTP the right protocol for transmitting computations?
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 19/21

24. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
CREST-Erlang
Erlang
Native support for
distribution
concurrency
fault-tolerance
The security problem
Computational REST
A possible evolution addressing the growing presence of
applications interfacing through the Web
Is HTTP the right protocol for transmitting computations?
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 19/21

25. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Future work
Caching mechanism, for improving performances especially for
static content
Introduce the concept of subpeer, part of the latest CREST
definition
Add more security mechanisms, for example for avoiding
possible attacks to a host
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 20/21

26. Introduction
The CREST-Erlang architecture
A performance assessment
Conclusions
Thank you
Questions?
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 21/21

27. Appendix
Related works
Dynamic adaptation
Publish-subscribe
Map-reduce
Web applications
REST
Service-Oriented Architecture
Context-oriented languages
ContextErlang
Dynamic Aspect-Oriented Programming
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 1/4

28. Appendix
Selected bibliography
J.R. Erenkrantz.
Computational REST: a new model for decentralized, Internet-scale
applications.
California State University at Long Beach, 2009.
R.N. Taylor, P. Oreizy and N. Medvidovic.
Runtime software adaptation: framework, approaches, and styles.
ICSE Companion 2008, 899–910, 2008.
J. Armstrong.
Programming Erlang: Software for a Concurrent World.
Pragmatic Bookshelf, 2007.
J. Zachary.
Protecting mobile code in the world.
Internet Computing, IEEE, 7(2):78–82, 2003.
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 2/4

29. Appendix
Code
The CREST-Erlang code can be found at:
https://github.com/sivieri/crest-erlang
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 3/4

30. Appendix
Licenses
This presentation is licensed under:
The image on slide 21 can be found at:
www.flickr.com/photos/29890539@N07/4648496819/
Sivieri, Cugola, Ghezzi Computational REST Meets Erlang 4/4