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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
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.
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
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
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
CLOUD COMPUTING
• Sharing Software, Platform, Infrastructure
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
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
THE COMPUTER NETWORK
• Hosts and Communications Subnet• WAN, LAN• IMPs, PSNs
• switches, hubs, bridges, gateways, routers
• Protocols• Arpanet, Internet• ISO/OSI, TCP/IP
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
SERVICES
• Email and Messaging• DNS, SMTP, TCP/IP
• WWW• HTML, HTTP, XML
• File Transfer• Telnet, SSH, FTP
• Social Networking
SERVICES
Social networking
Users/Browsers/
Web Clients
Web Servers
Distributed Database
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
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
SERVICES
Distributed Transaction Processing
Transaction manager
Replica manager
Transaction manager
Replica manager
network trans trans
Data manager
Data manager
database database
SERVICES
E-Commerce
payer payee
Acquiring institution
Issuing institution
Flow of money
network authorization
Payment order
notification
Request
1
2
3
4
5
SERVICES
Distributed Real-Time Processing
Device
Comp
Sensor Actuator
Device
Comp
Sensor Actuator
Device
Comp
Network
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
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
ISSUES
• Time and Coordination• What is the time?• Ordering of events
• Fault Tolerance and Recovery• Redundant elements• Logging schemes• Back-ups• Time-outs• Retransmissions
ISSUES
Scalability• Cannot assume a static configuration• Plan for growth• How about reduction?
USER-SYSTEM INTERFACE
• The Consumer• Look and Feel
• logically similar at all the host computers or front-end machines