Transcript pptx

Distributed Systems Foundations
Lecture 0
Evolution of computing history
• Main Frame with terminals
• Network of PCs & Workstations.
• Client-Server
• Now, moving forward to
Large cloud.
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Cloud Reality: Data Centers
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Cloud Computing: Why Now?
• Experience with very large datacenters
– Unprecedented economies of scale
– Transfer of risk
• Technology factors
– Pervasive broadband Internet
– Maturity in Virtualization Technology
• Business factors
– Minimal capital expenditure
– Pay-as-you-go billing model
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Economics of Cloud Users
• Pay by use instead of provisioning for peak
Resources
Resources
Capacity
Demand
Capacity
Demand
Time
Time
Static data center
Data center in the cloud
Unused resources
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Slide Credits: Berkeley RAD Lab
5
Economics of Cloud Users
• Risk of over-provisioning: underutilization
Capacity
Resources
Unused resources
Demand
Time
Static data center
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Slide Credits: Berkeley RAD Lab
6
Economics of Cloud Users
Resources
Resources
• Heavy penalty for under-provisioning
Capacity
Demand
Capacity
2
1
3
Time (days)
2
1
Lost revenue
3 Demand
Resources
Time (days)
Capacity
Demand
2
1
3
Time (days)
Slide Credits: Berkeley RAD Lab
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Lost users
7
Cloud Properties
• Commodity hardware
• Large Scale
• Elasticity
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Elasticity in the Cloud
Client Site
Client Site
Client Site
Load Balancer (Proxy)
App
Server
App
Server
App
Server
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App
Server
App
Server
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Why does this work?
• As long as requests are stateless, we can add
more resources, thus providing:
•Scale
•Elasticity
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But, most services need DATA!
• Challenges:
–How to scale with the increasing
amounts of data
–Where to store the data
–Accessing data on multiple sites
–Failures
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Need
• Fault-tolerance:
– Replication
• Large scale data:
– Partition data across multiple servers
• Multiple Servers:
– Time: clocks
– Coordination: mutual exclusion, leader election
– Consensus: Byzatine agreement, Paxos, etc
– Distributed state
– P2P
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Explosive Data Growth
• Wikipedia has over 3.5 million pages.
• Flickr members uploaded over 5 billion photos
• You Tube has 35 hours of videos uploaded each
minute
• “more video uploaded to YouTube in the past two
months than there would have been if ABC, CBS,
and NBC had been airing 24/7 since 1948!”
Gartner 2010
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Twitter 6th B’day: March 21, 2012
• First tweet: "inviting coworkers“, 2006
• a record of 6,939 tweets per second
immediately after Japan quake on March 11
2011, and 177 million tweets rest of the day.
• It took three years, two months and a day for
Twitter to get to one billion tweets.
• Twitter now averages 140 million tweets a day.
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