Chapter 2 Client Server Architecture

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Chapter 2Client Server Architecture
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Objectives

• Explain the essential principles of client-server
  architecture
• Explain the differences between 2-tier, 3-tier,
  and multitier architectures, including their
  features and relative capacities
• Recognize 2-tier, 3-tier, and multi-tier
  architectures
• Contrast the client-server architecture with
  centralized and distributed architectures

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System Architecture

• The architecture of a computer system is the
  high-level (most general) design on which the
  system is based
• Architectural features include
• Components
• Collaborations (how components interact)
• Connectors (how components communicate)

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System Architecture

• Common architectural patterns include
• Client-Server
• Layered
• Peer-to-peer
• Pipes and Filters
• etc.

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Client-Server Architecture

• Each component of a client-server system has the
  role of either client or server
• Client a component that makes requestsclients
  are active initiators of transactions
• Server a component that satisfies
  requestsservers are passive and react to client
  requests

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Centralized / Distributed

• The client-server architecture can be thought of
  as a median between
• Centralized processing computation is performed
  on a central platform, which is accessed using
  dumb terminals
• Distributed processing computation is performed
  on platforms located with the user

Centralized
Distributed
Client / Server
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Client-Server Architecture

• The Web is a client-server system
• Web browsers act as clients, and make requests to
  web servers
• Web servers respond to requests with requested
  information and/or computation

Client
Client
Server
Client
Server
request
Client
Server
Client
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Tiered Web Architectures

• Web applications are usually implemented with
  2-tier, 3-tier, or multitier (N-tier)
  architectures
• Each tier is a platform (client or server) with a
  unique responsibility

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2-Tier C-S Architecture

• Tier 1 Client platform, hosting a web browser
• Tier 2 server platform, hosting all server
  software components

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2-Tier Characteristics

• Advantage
• Inexpensive (single platform)
• Disadvantages
• Interdependency (coupling) of components
• No redundancy
• Limited scalability
• Typical application
• 10-100 users
• Small company or organization, e.g., law office,
  medical practice, local non-profit

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3-Tier C-S Architecture

• Tier 3 takes over part of the server function
  from tier 2, typically data management

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3-Tier Characteristics

• Advantages
• Improved performance, from specialized hardware
• Decreased coupling of software components
• Improved scalability
• Disadvantages
• No redundancy
• Typical Application
• 100-1000 users
• Small business or regional organization, e.g.,
  specialty retailer, small college

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Multitier C-S Architecture

• A multitier (N-tier) architecture is an expansion
  of the 3-tier architecture, in one of several
  different possible ways
• Replication of the function of a tier
• Specialization of function within a tier
• Portal services, focusing on handling incoming
  web traffic

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Replication

• Application and data servers are replicated
• Servers share the total workload

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Specialization

• Servers are specialized
• Each server handles a designated part of the
  workload, by function

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Portal Services

• Portal servers handle incoming traffic, reducing
  application server load
• e.g., firewall, load balancer, transaction
  processing manager

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Multi-Tier Characteristics

• Advantages
• Decoupling of software components
• Flexibility to add/remove platforms in response
  to load
• Scalability
• Redundancy
• Disadvantages
• Higher costs (maintenance, design, electrical
  load, cooling)
• Typical Application
• 1000 users
• Large business or organization

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Characteristics Summary

• large e-commerce, business, or organization
• small e-commerce, regional business or
  organization
• local business or organization

N-Tier
1000
3-Tier
users
100
2-Tier
10
capacity scalability redundancy cost
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Review

• Client-Server Architecture
• 2-tier, 3-tier, Multitier architectures