What is this course about? What do I mean by distributed information - - PowerPoint PPT Presentation

What is this course about?

What do I mean by “distributed information systems”?

• distributed: a bunch of computers connected by wires.

independent systems but not necessarily autonomous assume network supports messaging and stream communication how to use this to build distributed applications?

• information systems: focus on systems to store/access/share

data and operations on data.

Move data around and deliver it to the right places at the right times, safely and securely.

The Challenges of Distributed Systems

• location, location, location

Placing data and computation for effective and reliable resource sharing, and finding it again once you put it somewhere.

• distributed access to shared state

naming it, finding it, getting to it

• building reliable systems from unreliable components

reliable communication over unreliable network links autonomous computers can fail independently Lamport’s characterization: “A distributed system is one in which the failure of a machine I’ve never heard of can prevent me from doing my work.”

• private communication over public networks

Continuum of Distributed Systems

? ?

small fast big slow

LAN (NFS) Global Internet Parallel Architectures CPS 221

high latency low bandwidth autonomous nodes unreliable network fear and distrust independent failures decentralized administration

Networks CPS 214

Issues: naming and sharing performance and scale resource management low latency high bandwidth secure, reliable interconnect no independent failures coordinated resources

Multiprocessors clusters (GMS)

fast network trusting hosts coordinated slow network untrusting hosts autonomy

A Brief History

Dark Ages The Future

1960

ARPAnet Cedar Grapevine (Xerox PARC)

1970 1980 1990 1992 1995

DECnet SNA Ethernet LANs Berkeley Unix r* TCP/IP AppleTalk workstations RPC, NFS, NIS Apollo NSFnet V and Mach Emerald Argus ISIS AFS client/server DCE OMG Wintel PCs AOL IBM NT The Web Mosaic The Web The Web The Web distributed objects CORBA COM Java Java Java DES RSA DSM PVM/MPI Coda Tuxedo Encina Spring Network Objects search engines Viper Wolfpack Falcon, etc. ISPs Netscape commercial Internet Beans RMI servlets JINI ...

Current Trends #1

The business world has embraced the Internet, and is pushing to “open up” internal data for networked access.

• Automate internal processes, and deliver information to

where it will do the most good internally.

“Intranets”

• Connect to business partners, i.e., customers and suppliers.

“Extranets”

• Use the Web as a vehicle for PR and sales.

“e-commerce”

Needs: “component middleware”, clusters, security.

Current Trends #2

A telecommunications revolution is rapidly expanding access to public networks.

• new network plumbing to make “the last mile” digital

Replace “POTs” with fast/cheap network access to homes/offices.

• new wireless/mobile technologies

Implications:

• drives exponential growth of the Internet
• enables a new class of networked applications and

commercial online services

• creates demand for flexible service hosting by ISPs

The [Couloris et. al.] View (1990)

LAN hubs and bridges

workstations (and X-terminals) Unix sockets and r* client/server X windows RPC, NFS, NIS distributed Unix servers and resource managers PCs the Internet

(a million computers)

FTP, gopher, etc. (slow)

“Properties of Distributed Systems”

• 1. resource sharing (physical, logical, etc.)
• 2. open structure (standard interfaces, protocols, formats)
• 3. concurrency
• 4. scalability
• 5. fault tolerance and availability
• 6. transparency

access transparency, location transparency, concurrency transparency, scaling transparency, etc. name servers and server objects

Another View of Distributed Systems

standalone client apps Web browsers

extensible Web server back-end databases etc.

(“legacy”?)

front-end servers and component “middleware” (middle tiers)

clients

(first tier)

(borrowed without permission from http://www.byte.com/art/9710/sec6/art3.htm)