joel crichlow distributed systems: computing over networks, phi learning introduction to distributed...
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J O E L C R I C H L O WD I S T R I B U T E D S Y S T E M S : C O M P U T I N G O V E R N E T W O R K S , P H I L E A R N I N G
INTRODUCTION TO DISTRIBUTED SYSTEMS
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WHAT IS A DISTRIBUTED SYSTEM?
A Distributed System is a set of interconnected, autonomous computers that cooperatively solve large, single problems or facilitate parallel execution of separate but possibly related tasks.
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DISTRIBUTED SYSTEM
Computer network (hidden) network
User’s computer
Three key attributes:A network of computersThe network is hidden from the userThe system looks the same logically wherever the user is working
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CLOUD COMPUTING
• In general Cloud Computing provides access to a pool of computing resources
• Distributed System technologies support Cloud Computing
• Expect new buzz words in the near future
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CLOUD COMPUTING
• Recall the progressions• Uniprogramming to multiprogramming• Real memory to virtual memory• Real devices to virtual devices• Real machines to virtual machines
• More efficient and cost-effective use of resources• Cloud computing driven largely by the same
principles
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CLOUD COMPUTING
• Sharing Software, Platform, Infrastructure
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CLOUD COMPUTING
• Pay-per-use service alias Pay-as-you-go model• Uses a multi-tenant architecture to deliver several
categories of service
• Software as a Service (SaaS)• Delivers a single application
• Platform as a Service (PaaS)• Delivers development environments
• Infrastructure as a Service (Iaas)• Delivers storage, virtual machines, etc
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CLOUD COMPUTING
• Quick development• Good scalability• Public cloud
• Many end-user organizations use services from a common service provider
• Private cloud• Services are for a single organization
• Hybrid cloud
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THE COMPUTER NETWORK
• Hosts and Communications Subnet• WAN, LAN• IMPs, PSNs
• switches, hubs, bridges, gateways, routers
• Protocols• Arpanet, Internet• ISO/OSI, TCP/IP
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PROTOCOLS
. . . . . .
Host B Host A Communicates with
Layer n Layer n In layer n protocols
Layer 3 In layer 3 protocols Layer 3
Layer 2 In layer 2 protocols
Layer 2
Layer 1 In layer 1 protocols Layer 1
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SERVICES
• Email and Messaging• DNS, SMTP, TCP/IP
• WWW• HTML, HTTP, XML
• File Transfer• Telnet, SSH, FTP
• Social Networking
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SERVICES
Social networking
Users/Browsers/
Web Clients
Web Servers
Distributed Database
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SERVICESSOCIAL NETWORKING
• Facebook, Twitter, LinkedIn• Short Message Service (SMS)• Open source software• LAMP web application software stack
• Linux, Apache, MySQL and PHP
• In-house development• HipHop, Thrift and Cassandra
• Memcached: a distributed memory caching system
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SERVICES
• Multimedia Transfer• MPEG, MP3, RTSP
• Distributed Computation
Distributed applications
DCM middleware
Host OS and network service
Distributed applications
DCM middleware
Host OS and network service
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SERVICES
Distributed Transaction Processing
Transaction manager
Replica manager
Transaction manager
Replica manager
network trans trans
Data manager
Data manager
database database
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SERVICES
E-Commerce
payer payee
Acquiring institution
Issuing institution
Flow of money
network authorization
Payment order
notification
Request
1
2
3
4
5
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SERVICES
Distributed Real-Time Processing
Device
Comp
Sensor Actuator
Device
Comp
Sensor Actuator
Device
Comp
Network
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ISSUES
• Naming• Globally unique, Domains, Location
• Sharing• Authentication, Access rights• Scheduling, Coordinating, Synchronizing• Resolving conflicts
• Availability and reliability• Up-time, Responsive, Correct
• Replication• Copies made and stored at separate sites• Load sharing, Improved throughput, Improved availability
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ISSUES
• Privacy and Security• Passwords, Access Control Lists, Capabilities• Encryption, Memory Protection• Intrusion blockers
• Communication• Protocols aplenty
• Concurrency and Synchronization• Race Conditions• Critical Regions• Locks
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ISSUES
• Time and Coordination• What is the time?• Ordering of events
• Fault Tolerance and Recovery• Redundant elements• Logging schemes• Back-ups• Time-outs• Retransmissions
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ISSUES
Scalability• Cannot assume a static configuration• Plan for growth• How about reduction?
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USER-SYSTEM INTERFACE
• The Consumer• Look and Feel
• logically similar at all the host computers or front-end machines