F. Petroni and L. Querzoni: "HSIENA: a hybrid publish/subscribe system." In: Proceedings of the 1st International Workshop on Dependable and Secure Computing for Large-scale Complex Critical Infrastructures (DESEC-LCCI), 2012. Abstract: "The SIENA publish/subscribe system represents a prototypical design for a distributed event notification service implementing the content-based publish/subscribe communication paradigm. A clear shortcoming of SIENA is represented by its static configuration that must be managed and updated by human administrators every time one of its internal processes (brokers) needs to be added or repaired (e.g. due to a crash failure). This problem limits the applicability of SIENA in large complex critical infrastructures where self-adaptation and -configuration are crucial requirements. In this paper we propose HSIENA, a hybrid architecture that complements SIENA by adding the ability to self-reconfigure after broker additions and removals. The architecture has a novel design that mixes the classic SIENA’s distributed architecture with a highly available cloud-based storage service."

1. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA
a hybrid publish/subscribe system
Fabio Petroni
Leonardo Querzoni
Department of Computer, Control, and Management Engineering Antonio Ruberti
Workshop on Dependable and Secure Computing
for Large-scale Complex Critical Infrastructures
Magdeburg, 25 september 2012

2. Magdeburg sept 25 2012 DESEC4LCCI
Publish/subscribe paradigm
The publish/subscribe interaction scheme [1]
provides a form of communication, alternative to
the standard clients/server model, where
participants are decoupled with respect to:
TIME
The participants do not
need to be active at
the same time,
publishers might
publish events while
some subscribers are
disconnected, and
subscribers might get
notified about some
events while the
original publisher is
disconnected
SPACE
The interacting
parties do not need
to know
each other. An event
notification service
(ENS) is responsible
to gather publishers
issued events and to
diffuse them toward
the subscribers
SYNCHRONIZATION
An event is
asynchronously
propagated to all
subscribers that
registered interest
on it, and publishers
are never
blocked while
producing events
1

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CONTENT BASED
Subscription:
conjunction of predicates.
TOPIC BASED
Subscription:
set of topics
Static schema
Limited expressiveness
Topic-based vs Content-based
Broker Publisher / Subscriber
football news
Event Notification Service
News= football
Team= Lazio
Year > 2010
SIENA
Routing Scheme
[2,3]
2

4. Magdeburg sept 25 2012 DESEC4LCCI
SIENA 3
PHYSICAL OVERLAY
BROADCAST
LAYER
CONTENT-
BASED
LAYER
“all-pairs
path
symmetry”

5. Magdeburg sept 25 2012 DESEC4LCCI
The problems of SIENA
SIENA suffers by the lack of adequate
support to system reconfiguration
In particular the addition or the removal of a
new node to the system requires a full halt,
followed by a manual reconfiguration of the
broadcast and the content-based layers
This can lead to large management
overhead and reduced performance in
dynamic or large-scale environments
GOAL: make SIENA layers self-organizing, so
that the whole system needs a reduced
management by human administrators
4

6. Magdeburg sept 25 2012 DESEC4LCCI
Related work
XSIENA [4] proposes a soft state approach
The idea is to use timed subscriptions, and
re-issue them periodically, in order to
automatically manage and restore the state
of crashed subscribers and publishers
Cugola et al. [5] proposed a solution for the
single broadcast tree case, limiting the
reconfiguration to a well defined path
Moreover, they have clearly defined the
reconfiguration problem
5

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Reconfiguration problem 6
PHYSICAL OVERLAY
BROADCAST
LAYER
CONTENT-
BASED
LAYER

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Reconfiguration problem 6
PHYSICAL OVERLAY
BROADCAST
LAYER
CONTENT-
BASED
LAYER
reconfiguration of the overlay network
to maintain connectivity among participants
1
BROADCAST
LAYER

9. Magdeburg sept 25 2012 DESEC4LCCI
Reconfiguration problem 6
PHYSICAL OVERLAY
BROADCAST
LAYER
CONTENT-
BASED
LAYER
reconfiguration of the overlay network
to maintain connectivity among participants
1
BROADCAST
LAYER
reconfiguration of the subscription information
to bring the routing tables up-to-date with the changes
2
CONTENT-
BASED
LAYER

10. Magdeburg sept 25 2012 DESEC4LCCI
Reconfiguration problem 6
PHYSICAL OVERLAY
BROADCAST
LAYER
CONTENT-
BASED
LAYER
reconfiguration of the overlay network
to maintain connectivity among participants
1
BROADCAST
LAYER
reconfiguration of the subscription information
to bring the routing tables up-to-date with the changes
2
CONTENT-
BASED
LAYER
minimization of event loss
during reconfiguration
3

11. Magdeburg sept 25 2012 DESEC4LCCI
IDEA
How do we coordinate the brokers in the system, since they are
geographically spread, independent and possibly linked by
networks with unpredictable latency (like internet)?
Solutions based on a central coordinator may be inefficient for
several reasons:
fault tolerance (single point of failure)
organizational (different administrative domains)
scalability
PROPOSAL: use a storage system reliable and easily accessible by
all processes in the system, supplied by a cloud provider
The cloud provider takes care of maintaining the storage available
and consistent
We only have to manage concurrent accesses of brokers to this
storage
Montresor and Abeni (2011)[6] proposed a similar idea in the
context of gossip algorithms
7

12. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA 8
Cloud Service
Storage
epoch number
Pred D
PHYSICAL OVERLAY

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HSIENA – insertion of a new broker 1/2 9
Cloud Service
Storage
PHYSICAL OVERLAY
BROADCAST
LAYER
Pred
D

14. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – insertion of a new broker 2/2 10
Cloud Service
Storage
PHYSICAL OVERLAY
BROADCAST
LAYER
EPOCH UPDATE
Pred
D

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HSIENA – reconfiguration of the overlay network 11
Pred
PHYSICAL OVERLAY
BROADCAST
LAYER
SELECT

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HSIENA – reconfiguration of the subscription info 12
PHYSICAL OVERLAY
BROADCAST
LAYER
CONTENT-
BASED
LAYER
1
2
3
PULL
UPDATE

17. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 1/7
< i, [INS/REM], y, V >
“The broker y is performing a [INS/REM]
operation that will bring the system to
epoch i. V is a set of broker ids used
only for INS operations (neighbors of y)”
Assumption: the storage service provides
a test-and-set primitive
13
Ops
en queue of
ongoing
operations

18. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 2/7 14
3
21 A
3
21
B
i
< i+1, INS, A, {1,2} > < i+1, INS, B, {2,3} >

19. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 3/7 14
Ops
3
21 A
3
21
B
ien
< i+1, INS, A, {1,2} > < i+1, INS, B, {2,3} >
T&S T&S

20. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 4/7 14
Ops
3
21 A
3
21
B
ien
AA
pending
< i+2, INS, B, {2,3} >START INSERTION PROCEDURE

21. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 5/7 14
Ops
3
21 A
3
21
B
ien
A
START INSERTION PROCEDURE
T&S
PERFORM A's INSERTION
START INSERTION PROCEDURE

22. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 6/7 15
Cloud Service
Storage
i i+1 i+2
A
Blist of couples
of matrices

23. Magdeburg sept 25 2012 DESEC4LCCI
HSIENA – Concurrency 7/7
If B succedes, A omits the epoch update.
As last step, the entry in Ops is deleted
16
3
21 A
3
21
B
i
A
i+2i+1
T&S T&S

24. Magdeburg sept 25 2012 DESEC4LCCI
Conclusions and future works
HSIENA is a hybrid system that complements the SIENA
publish/subscribe system by adding the ability to self-
reconfigure after brokers additions and removals.
HSIENA has a novel design that mixes the classic SIENA’s
distributed architecture with a highly available cloud-
based storage service that brokers use as a shared
memory space they can rely-on to adapt at runtime the
ENS application-level network without service disruption.
We are implementing a prototype of HSIENA to test its
behaviour under various realistic loads.
Our purpose is to asses both its ability to support
insertion and deletions while providing service continuity
and to study the tradeoff existing between the level of
service HSIENA can guarantee and the cost incurred for
maintaining state information stored on a cloud service.
17

25. Magdeburg sept 25 2012 DESEC4LCCI
References
[1] R. Baldoni, L. Querzoni, S. Tarkoma, A.
Virgillito: “Distributed Event Routing in
Publish/Subscribe Communication Systems”.
Springer (2009)
[2] A. Carzaniga, D. Rosenblum, A. Wolf: “Design
and evaluation of a wide area notification
service”. TOCS (2001)
[3] A. Carzaniga, M.J. Rutherford, A. Wolf: “A
routing scheme for content-based networking”.
INFOCOM (2004)
[4] Z. Jerzak, C. Fetzer: “Soft state in
publish/subscribe”. DEBS (2009)
[5] G. Cugola, D. Frey, A.L. Murphy, G.P. Picco:
“Minimizing the Reconfiguration Overhead in
Content-Based Publish-Subscribe”. SAC (2004)
[6] A. Montresor, L. Abeni: “Cloudy weather for
P2P, with a chance of gossip”. P2P (2011)
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