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Definition
• What is a distributed system?
Leslie Lamport
”You know you have a distributed system when the crash of a computer you have never heard of stops you from getting any work done.”
We counteract this definition!
Distributed Systems
• Example of distributed systems:– File systems–Web servers–Mail servers– Databases
Frequently, an organization stores all its
files on a centralized distributed file server
If it fails, no one can access their files
Webb servers often become overloaded and
fail
The central mail server crashes, no one can read their email!
Our effort
• Build on an 30-year old idea
• Arpanet, the precursor of Internet, was built for:– Military survivability
• If some part stops working, the rest should continue to function
• Internet has been quite successful so far…– No fail-stop yet
• But the effort stopped here…
Peer-to-Peer System
• We want to build– Services– Servers– Applications
• That are self-managed
• Achieved by peer-to-peer techniques!
Peer-to-Peer Middleware
• After several years of research– Built a middleware: DKS
• Provides:– Routing services– Directory services – Name-based messaging
(multicast/publish/subscribe)
Peer-to-Peer System
• DKS is self-managing
• Automatic managent:– Adding servers/resources– Removing servers/resources
– Crash of servers/resources
– Load balancing of data/nodes– Security
Peer-to-Peer?
• How is it different from:– KaZaa– Napster– Gnutella– Skype
• These are so called unstructured p2p systems– Limited applicability (file sharing)– Inefficient (wastes bandwidth)
• Our focus is on structured p2p systems– Chord/CAN/Pastry (USA)– DKS/P-Grid (Europe)
What can we do with DKS?
• Three concrete applications:– P2P Web server– P2P Backup– P2P File system
P2P Web
• Works like an ordinary web server
• Differences:– It is distributed– Automatic data
replication– Load-balancing
of users
• Too much load– Add another
server
Publish your web pages
Gets stored on the DKS
0 1
2
3
4
5
67
89
10
11
15
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115
13
4
5
Store it here
Store a new copy here
Store a copy here
P2P Backup
• Initialization– Install a client on your computer– Decide on amount of space to share– Choose files for backup
• Regular backup– Data is encrypted– Always accessible
Conclusion
• Structured Peer-to-Peer system– Self-organizing
• Automatic fault-tolerance• Automatic addition of nodes/resources• Automatic removal of nodes/resources• Automatic load-balancing
• Many interesting applications– File systems– Backup– Web– M.m.
• Cost-saving for companies– Save money on administration
