Lecture Operating systems: Internals and design principles (6/E): Chapter 16 - William Stallings

Chapter 16 - Client/server computing. In this chapter, we begin with an examination of some of the key concepts in distributed software, including client/server architecture, message passing, and remote procedure calls. Then we examine the increasingly important cluster architecture.

Operating Systems:

Internals and Design Principles,

6/E William Stallings

Chapter 16 Client/Server Computing

Patricia Roy

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- Client machines are generally single-user

PCs or workstations that provide a highly user-friendly interface to the end user

‘ Each server provides a set of shared

services to the clients

‘ The server enables many clients to share

access to the same database and enables

the use of a high-performance NHI

system to manage the database

Applications Programming Interface (API)

A set of function and call programs that allow clients and servers to intercommunicate

Structured Query Language (SQL)

A language developed by IBM and standardized by ANSI for addressing creating

updating or querying relational databases

Figure 16.1 Generic Client/Server Environment

Client/Server Applications

- Basic software is an operating system

running on the hardware platform

‘ Platforms and the operating systems of

client and server may differ

- These lower-level differences are

irrelevant as long as a client and server Share the same communications protocols and support the same applications

Application logic 1 ȓ Application logic

response

software interaction _ Protoco software

* Application logic is located at the client

- Presentation services in the client

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HS

-

\ Database Applications

- The server is a database server

- Interaction between client and server Is In

the form of transactions

— the client makes a database request and receives a database response

- Server is responsible for maintaining the

database

Database logic -®—— Database logic

response Communications ` oe software I} protocol | Communications [Database management

interaction software system

_ WGlient/Server Database Usage

_ ÑGlient/Server Database Usage >>

(b) Misused client/server

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“= Classes of Client/Server

_ Host- based processing

— Not true client/server computing

— Traditlonal mainframe environment

-Š Classes of Client/Server

_Server- based processing

— Server does all the processing

— Client provides a graphical user interface

-$ Classes of Client/Server

Applications

_Client- based processing

— All application processing done at the client

- Data validation routines and other database logic functions are done at the server

- Application software distributed among

three types of machines

By Figure 16.6 Three-tier Client/Server Architecture

- Caches are consistent when they contain

exact copies for remote data

* File-locking prevents simultaneous access

to a file

_#

Istributed File Cacheing tn

Traffic Client Traffic Server Traffic Client Traffic

Middleware

- Set of tools that provide a uniform means

and style of access to system resources across all platforms

* Enable programmers to build applications

that look and feel the same

- Enable programmers to use the same

method to access data

interaction software services

Client Server operating system

_ \bistributed Message Passing re

Application Message-Oriented

Middleware

Application Message-Oriented Middleware

(with message queue) Application-specific (with message queue)

(a) Message-Oriented Middleware

_ )Bistributed Message Passing

program Application-specific program

_ \bistributed Message Passing

and responses and responses

(c) Object request broker

_#

Object requests Object requests

@liability versus Unrellability

- Send the message out into the

communication network without reporting success or failure

—- Reduces complexity and overhead

locking versus Nonblocking

Remote Procedure Calls

- Allow programs on different machines to

Interact using simple procedure call/return semantics

, ‘Remote Procedure Call

Remote server

application

Client application

response response

Local Local response procedure

Local application Salata

operating system RPC [Re - 2 2 ee ee ee eee RPC

Mets mm ee ee eee ee ee ee ee mechanism

Remote procedure call

Figure 16.12 Remote Procedure Call Mechanism

_.®

N -_ Client/Server Binding

- Binding specifies the relationship between

remote procedure and calling program

—- Does not block the caller

—- Enable a client execution to proceed locally in parallel with server invocation

_#

bject-Oriented Mechanisms

- Clients and servers ship messages back

and forth between objects

- Aclient sends a request to an object

broker

- The broker calls the appropriate object

and passes along any relevant data

— |llusion is one machine

— System can run on Its own

— Need management or scheduling software

- Data must be constantly copied among systems so each Is current

Clusters

- Shared nothing

- Reduces communication overhead

—- Disks partitioned into volumes

- Each volume owned by a computer

— If computer fails, another computer has ownership of the volume

takes over in case of

primary server failure

Clustering Method Description Benefits Limitations

Passive Standby A secondary server Easy to implement High cost because the

secondary server is unavailable for other processing tasks

The secondary server

is also used for processing tasks Reduced cost because

secondary servers can

be used for processing Increased complexity

and Limitations

_ \€lustering Methods: Benefits

Separate Servers Separate servers have | High availability High network and

their own disks Data server overhead due

is continuously copied to copying operations from primary to

secondary server

Servers Connected | Servers are cabledto | Reducednetworkand | Usually requires disk

to Disks the same disks but server overhead due muroring or RAID

each server owns its to elimination of technology to

disks If one server fails its disks are copying operations compensate for risk of

access to disks Reduced risk of Usually used with

downtime caused by disk mirroring or disk failure RAID technology

ej Operating System Design

— Fault-tolerant cluster ensures that all

resources are always available

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Uster Computer Architecture

Ỉ =a

SS

> *,*

- Cluster middleware services and functions

— Single entry point

— Single file hierarchy

— Single control point

— Single virtual networking

Uster Computer Architecture

Ỉ =a

SS

> *,*

- Cluster middleware services and functions

— Single memory space

— Single job-management system

— Single user interface

— Single I/O space

- \luster Computer Architecture

- Cluster middleware services and functions

- Single process space

- Checkpointing

- Process migration

High Speed Network/Switch

Figure 16.14 Cluster Computer Architecture [BUY Y99a]

Clusters Compared to SMP

- SMP Is easier to manage and configure

- SMP takes up less space and draws less

power

- SMP products are well established and

Stable

~~ Windows Cluster Server

- Cluster Service

-— Collection of software on each node that

manages all cluster-specific activity

App ¢ Failover Mgr - ‘ Other

Resource Resource Mgr “MẸ 7.“ Nodes

Resource Monitors) > > Resource

Management Interface App

Resource

luster-aware App

Figure 16.15 Windows Cluster Server Block Diagram [SHOR97]

Nê ` Sun Cluster Structure ;

Existing Solaris Kernel

5un Cluster File System

system system system system

Figure 16.17 Sun Cluster File System Extensions

—- Mass market commodity components

—- Dedicated processors (rather than scavenging cycles from idle workstations)

— Adedicated, private network (LAN or WAN or internetted combination)

- ÀBeowulf and Linux Clusters

- Key features

- Scalable l/O

- ATreely avallable software base

— Use freely available distribution computing tools with minimal changes

- Return of the design and improvements to the community

_ ——_— 8

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*

eric Beowulf Configuration

Distributed shared storage