CS556: Distributed Systems

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CS-556 Distributed Systems
Jini JXTA

• Manolis Marazakis
• maraz_at_csd.uoc.gr

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Distributed programming

• Distributed computing is more difficult than
  local computing because of
• Network latency
• Concurrency issues
• Memory (state) management
• Inevitable partial failure

Remote increasingly looks like local
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Jini

• A set of interfaces protocols
• Spontaneous networking
• Federations of software services and/or devices
• H/W S/W entities are represented by Java
  objects
• Located accessed via Java interfaces
• Self-healing networks
• Vision
• Make the installation use of devices app.
  software as simple as plugging in a phone
• Java tone

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Jini Java

• Java VM
• homogeneous network
• Portable object code
• architecture independence
• Downloadable code
• dynamic environment
• Unified type system

• Key component
• Lookup Service
• repository of service proxies
• Clients download services
• on-demand

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Using the Lookup service
Clients inquire by service type
Discovery Join protocols - based on UDP
multicast
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Discovery Join

• Traditional Technology
• Device is added to computer
• Device definition is edited in node configuration
  table
• Computer is restarted
• Updated configuration table is pushed to network
  device map

• Jini Technology
• Device is plugged in powered up
• Lookup service receives multicast
• Lookup service authenticates source
• Lookup service sends advertisement
• Device joins Lookup service

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Finding using a service

• Communication is bet. the service
• its proxy
• Independent of wire protocol
• Protocol can change without
• affecting client
• - RMI semantics

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Distributed leasing (I)

• Protocol for managing resources using a
  renewable, duration-based model
• Contract between objects (grantor holder)
• Resources can be shared or private
• Provides a method of managing resources in an
  environment where partial failures occur
• Time-based grants of resources or services
• Negotiated for a set period of time
• Can be shared or exclusive
• Leases may be
• Cancelled (explicit cleanup)
• Renewed (explicit extension)
• Allowed to expire (implicit cleanup)
• Obtained manipulated by 3rd parties

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Distributed leasing (II)

• Resources are allocated only as long as continued
  interest is shown
• The lease holder is responsible to renew lease
  before expiry
• The network is self-healing

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Distributed Events

• Extend Java event model to work in a distributed
  network
• Register interest, receive notification
• Allow for use of event managers
• Support various delivery models
• Push, pull, filter
• Use the Distributed Leasing protocol

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Distributed transactions

• Designed for distributed object coordination
• Light weight, object-oriented
• Supports two-phase commit
• Uses Distributed Leasing protocol
• Implemented in Transaction Manager service

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Jini JavaSpaces
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Architecture layers
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Communication Events
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Processes (I)

• A JavaSpace can be replicated on all machines.
  The dotted lines show the partitioning of the
  JavaSpace into subspaces.
• Tuples are broadcast on WRITE
• READs are local, but the removing of an instance
  when calling TAKE must be broadcast

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Processes (II)

• Unreplicated JavaSpace.
• A WRITE is done locally.
• A READ or TAKE requires the template tuple to be
  broadcast in order to find a tuple instance

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Processes (III)

• Partial broadcasting of tuples template tuples.

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The Jini Lookup Service (I)
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The Jini Lookup Service (II)

• Examples of predefined tuples for service items.

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Synchronization of Transactions
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PAM
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Evolution of network computing
C/S model is increasingly seen as a limiting
factor !
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Motivation for peer-to-peer (p2p)

• Vast underutilization of Internet assets
• Information
• World data production 2x1018 bytes/year
• Published 3x1012 bytes
• Transient data cannot be captured by Web crawlers
• Google 1.3x108 pages
• Bandwidth
• x 106 increase since 1975
• x2 every 16 months
• Yet hot spots remain !
• Computing resources
• Concentrated in data centers
• Crippling rate of increase of workloads
• Hard to keep up with demand !

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JXTA software architecture
Platform- transport-independent protocols
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JXTA concepts (I)

• UUID 128-bit internal identifier per entity
• Must be explicitly bound to external name to form
  a security principal
• The authenticity of the binding can be ensured by
  including digital signatures
• Advertisement
• XML document that names describes the existence
  of a resource
• Peer, peer group, pipe, services (codats)
• Messages
• Datagram-like, assuming unreliable, asynchronous,
  uni-directional transport
• Envelope header, msg digest, source end-point
  (optional), destination end-point
• Stack of protocol headers bodies
• Variable number of bytes security credentials

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JXTA concepts (II)

• Peers
• any entity that can interact with (a subset of)
  the JXTA protocols
• End-point
• a URI identifying a logical destination on a
  transport that supports datagram-like messaging
• Peer group
• a collection of co-operating peers
• Eg in the context of a service
• World Peer Group
• Pipes
• Asynchronous, uni-directional comm. Channels
• A pipes end-point can be bound to one or more
  peer end-points
• Usually dynamically, at run-time

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JXTA protocols

• Peer discovery
• Find advertisements
• Peer resolver
• Search for peers, peer groups, pipes,
• Peer information
• Inquire a peers capabilities status
• Peer membership
• Obtain group membership requirements
• Specs of credentials, authenticator,
• Apply for/update/cancel membership
• Pipe binding
• Bind an advertisement to a pipe end-point
• End-point routing
• Ask a peer router for available routes for a
  destination
• Peers may not be directly connected
• Different transports, Firewalls, NATs

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JXTA Shell (I)

• Command-line access to the JXTA platform
• Publish, search execute codats
• Discover peers groups
• Create pipes to connect peers
• Send/receive messages
• Stdin default input pipe
• Stdout default output pipe
• Pipes can be dynamically disconnected
  reconnected
• cat myfile grep jxta
• cat myfile gtp1 grep ltp1 jxta
• grep ltp1 unix

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JXTA Shell (II)

• cat
• Display advertisement, message, structured
  document (as read using importfile)
• mkpipe io ltpipe-advgt
• mkmsg
• send ltoutPipegt ltmsggt
• recv -t lttimeoutgt ltinPipegt
• Codats can be imported into codat containers
• share ltURIgt
• Currently, only local file// URIs are supported
• Symbolic name size MIME type encoding
• ls
• listing of codats currently cached by the local
  peer
• For the current peer group

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JXTA Shell (III)

• whoami -g
• Display the local peers or current peer groups
  advertisement
• mkadv
• mkgrp
• chgrp
• join
• leave
• peers r
• Propagate peer inquiry
• Results are cached locally
• peers
• Display currently known peers
• peerinfo ltidgt
• groups

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References

• Jini Network Technology Web site
• http//www.sun.com/jini/
• Jiniology articles
• http//www.artima.com/jini/jiniology/
• JXTA project Web site
• http//www.jxta.org/