The Virtual OSGi Framework - Jan Rellermeyer

© 2008 by Jan S. Rellermeyer, ETH Zurich; made available under the EPL v1.0 | March 19th 2008
The Virtual OSGi Framework
Systems Group
Department of Computer Science
ETH Zurich
8092 Zurich, Switzerland
Invited Researcher of
the OSGi Alliance
Jan S. Rellermeyer
“Inaugural Talk”

The Virtual OSGi Framework | © 2008 by Jan S. Rellermeyer, ETH Zurich; made available under the EPL v1.0
Virtual OSGi? VOSGi?
• Unintended name clash
• VOSGi is work by Stephane Frenot et. al.
• Share services among virtual gateways
[Y. Royon, S. Frenot: Un environnement multi-utilisateurs orienté service. In: CFSE 2006]
More like OS-
Virtualization

Remember EclipseCon 2007…
• R-OSGi
• Originally motivated by embedded systems
• Service Discovery via SLP
R-OSGi
Presentation
R-OSGi
EventAdmin
EventAdmin
RobotDevice
RobotDevice
EventHandler
Proxy
Bundle
[J. S. Rellermeyer, G. Alonso, and T. Roscoe: R-OSGi: Distributed Applications Through Software
Modularization. In: Middleware 2007]
Services were
described by SLP
Service URLs

R-OSGi Today
• Point to point
• Explicit connections
• Service Discovery is an optional part
• Closer to OSGi
RemoteServiceReferences known
after lease exchange
Proxy is generated when the service
is retrieved by a client
More feasible for
remote services on the
server side.
Gives “hints” where to
connect to.
Already synchronized
Transparently “import”
the remote service into
the local framework

R-OSGi as an ECF Remote Service Provider
• ECF API on top of R-OSGi
• Thereby, non-transparent access on top of a
transparent service approach
• E.g., asynchronous service invocation
DSO on an ECF
server
Transparent, point to
point remote services

Motivation: Distributed Service Registry
• Original R-OSGi
Service Discovery
• R-OSGi 1.0.0.RCs
Pair wise joined Service Registry
Still service registry and remote service registry
• ECF Generic Provider
Server and DSOs
• Other possibility: Unified service registry for both local
and remote services
“The network is the
service registry”
“Remote Service
Registry = union of
connected service
registries”
“Centralized service
registry”
The Virtual OSGi
Framework

Motivation: Tool for “Orthogonal Distribution”
Demo
[Jan S. Rellermeyer, Gustavo Alonso, Timothy Roscoe: Building, Deploying, and Monitoring Distributed Applications
with Eclipse and R-OSGi. In: Eclipse Technology eXchange (ETX) Workshop (in conjunction with OOPSLA 2007)].

How does it work?
Proxy Bundle Channel
Endpoint
Service
Channel
Endpoint
Channel
Endpoint
Channel
Multiplexer

The Problem of State
• Failover
• Load balancing
• Real Services are not always stateless.
• Couldn’t state be preserved?
• Service replicas instead of just copies?
Think of the web
Task for the
middleware
The Virtual OSGi
Framework

Motivation: Sensor Nodes as OSGi Services
• TMote Sky
TI MSP430F1611 microcontroller at up to 8 MHz
10k SRAM, 48k Flash + 1024k serial storage
250kbps 2.4 GHz Chipcon CC2420 IEEE 802.15.4 Wireless
Transceiver
• Cannot even run an OS
Runs TinyOS
• But it can be an R-OSGi service…
[J.S. Rellermeyer, M. Duller, and G. Alonso. Using Non-Java OSGi Services for Mobile Applications.
Demo at: MiNEMA 2008 Workshop in conjunction with EuroSys 2008].
Demo
[with Michael Duller]

Extending the Idea of OSGi Services
• C/C++
• CLDC
• Over Bluetooth, …
[J.S. Rellermeyer, M. Duller, K. Gilmer, D. Maragkos, D. Papageorgiou, and G. Alonso: The Software Fabric
for the Internet of Things. In: Internet of Things 2008].
Why should a remote
OSGi service have to be
written in Java?
Would be nice to have this for local
services as well
The Virtual OSGi
Framework

What about consuming services
• The consumer has to be an OSGi framework
• But, …
• Couldn’t it be
The Virtual OSGi
Framework

The Virtual OSGi Framework
• OSGi on the cloud
Have a network full of machines running OSGi
Don’t care where they are
Don’t care where bundles are installed
Don’t care where services are provided
Access them from anywhere
• Fluid OSGi
Have a replica where you need it
Read any / write any
Bundles and services
are becoming virtual
Access them
transparently
From a peer’s
perspective, services
“flow” through the
network

Architecture
• Unifying local and remote services
• As an extension, non-invasive against the framework

Architecture
• Unifying local and remote services
• As an extension, non-invasive against the framework
Equivalent for a peer
on the cloud

Virtualized Module Layer
• The Virtual Framework runs as a
bundle on the host framework
• Virtual Bundles are installed on the
host framework
• Virtual Bundles are started on the
virtual Framework
[Dimitrios Papageorgiou]
Host framework

Virtual Bundles
• Installation of the bundle
• Install on the host framework
• Pass back a VirtualBundle instead of the
host framework’s Bundle implementation
• Starting the bundle
• Called through a VirtualBundle
• get the Activator from the host framework
• Call it with a VirtualBundleContext
• Handle the virtual state of the bundle within
the virtual framework
• Subtile: ensure BundleID consistency

Distributed Registries
• Centralized registries are
replaced by a distributed
registry
• Prototype system: kind of
DHT
Can store pointers to
bundles
Supports constraints
Can store pointers to
services + attributes
Supports filters

Challenges
• Mapping the class space model to the DHT
•getAllServices becomes a very expensive
operation
• Maintaining replicas of DHT nodes
• Scalability?
Can it scale to massively distributed systems?
Can it scale to the diameter of the internet?
Optimization for
resolving
Is there a good
Tradeoff?
Transactional model?
Currently not our
focus!

OceanStore?
[J. Kubiatowicz, D. Bindel, Y. Chen, S. Czerwinski, P. Eaton, D. Geels, R. Gummadi, S. Rhea, H. Weatherspoon, W. Weimer, C.
Wells, and B. Zhao: OceanStore: An Architecture for Global-Scale Persistent Storage. In: ASPLOS 2000]

Service Replication
• Fluid Replication
Place a replica of the service where ever it
is needed
• Preserve the state between service
replicas
• Prototype: Communication model
through the DHT
• Coordinator nodes
For update propagation
For using different consistency levels within
the same virtual framework
[Damianos Maragkos]

PRACTI?
• Partial Replication
• Arbitrary Consistency
• Topology Independence
[N. Belaramani, M. Dahlin, L. Gao, A. Nayate, A. Venkataramani, P. Yalagandula, and J. Zheng: PRACTI
Replication. In: NSDI 2006]

Replication of Services
• What is state?
Model: Only services have state
State is contained in fields
• Capturing state?
Update propagation
Arbitrary consistency
• Goal: Transparent replication
Run with every OSGi Service
Requires no changes

OpenTerracotta?
• Transparent clustering
• Load time instrumentation
• Distributed locking
[http://www.terracotta.org]

Instrumentation
• Symbolic Execution
• Instrumentation to capture fields
• Also does distributed locking, distributed thread
coordination
• Also used for service migration
Find out where state is
accessed/changed
P2P update propagation
through group
communication
Seamless parallelization
Can be considered as a
temporal replication
But we also handle
thread migration.

What we have now…

Coordination overhead
• Coordinating all the replicas
• Affects scalability
Duality between
Service Replicas and
Remote Services

Outlook: Autonomous Controller
[Ramon Küpfer, Dario Simone; starting soon]

Outlook: Language-independent OSGi
• Soon a prototype for Barrelfish (new operating system
at ETH)
Use the kernel-provided IPC model
Provide an application model
(derived from OSGi)
Optimize for interactions within
the same language
Provide generic type mappings
for heterogeneous apps
[with Simon Peter, Adrian Schüpbach,
Andrew Baumann, Timothy Roscoe]

Conclusions
• The Virtual OSGi Framework
Unifies local and remote services
Makes a (dynamic) group of machines appear as a single
OSGi framework
Allows replication of services for load balancing or to
increase failure resilience
Runs as a bundle on top of every framework
Uses the host framework for module layer operations
Intercepts/extends certain operations on the
virtualization layer
Can relocate bundles/services
OSGi on the cluster/cloud

Welcome to the virtual world!
• Questions?

The Virtual OSGi Framework - Jan Rellermeyer

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