20215581 Topics in Computer Science G Distributed Object Programming

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202-1-5581 Topics inComputer Science
GDistributed Object Programming

• Ronen Kat
• Ben Gurion Univiersity 2003

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• Distributed System
• Overview

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Computer Systems

• Wish list
• Scalable
• Fast
• Reliable no faults
• Secure
• Easy and fast to program
• High data integrity

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Computer Systems (cont)

• Distributed
• Multiple computers working together
• Located far away
• Improve stability and availability
• Middleware
• Transactional
• Data integrity
• Secure communication and storage

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This Course

• The technology
• The methods and tools
• The problems
• The grade
• 60 Assignments
• 40 Quiz

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References

• Distributed Systems Principles and Paradigms /
  Tanenbaum, Van Steen
• Client/Server programming with JAVA and CORBA 2nd
  edition / Orfali, Harkey
• The Wide World Web

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Topics

• Remote access protocols
• Transaction Processing
• Database Technology
• Security
• Load-balancing and Scalability
• Distributed Application Architectures and
  Integration

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Topics (cont)

• Web Technology
• CORBA Technology and Systems
• COM/.NET and EJB
• XML/XSL/SOAP and the Web Services
• Grid computing

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Technology Background

• Uniprocessor / Multiprocessor machines
• Homogeneous/Heterogeneous systems
• Distributed OS
• Uniprocessor OS
• Multiprocessor OS semaphore and monitor

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Technology Background (cont)

• Multi computer OS
• Shared memory
• Message passing
• Network OS
• Global file systems
• Remote execution

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The Client Server Model

• Server a process implementing a specific
  service.
• Client a process that requests a service from
  servers by sending a request and waiting for a
  reply.

Client
Wait for service
Reply
Request
Server
Provide service
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File Server Example

• System constants
• File operations
• Result codes
• Message format

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File Server Example Server

• Main loop
• Receive message
• Block for message
• Per opcode handle message
• Return result at m2

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File Server Example File Copy

• Copy file SRC to DST on server
• Body
• Read block
• Write block
• Until end of file

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Application Layers

• Who is a Server?
• Who is a Client?
• User interface
• Processing business logic
• Data storage

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User Interface

• Implemented in clients
• Handles user interactions
• Examples
• Character based terminals
• Windowing software
• Internet browser

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Processing - Business Logic

• Business rules
• Data analysis
• The what to do with user interaction on data.

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Data Storage

• Maintains the actual data
• Provides persistent data
• Typically implemented on a server
• Consistency
• Constraints
• Meta data

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Client Server Architectures

• 2 tier applications
• Client vs Server
• Multi tier applications
• User interface
• Application
• Database
• A 3 tier implementation

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What is Middleware?

• Software plumbing
• and
• associated services
• for building
• distributed systems

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Models

• Distributed file systems
• Remote procedure calls (RPCs)
• Distributed Objects
• Distributed Documents

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Services

• Makes distributed computing look like local
  computing
• Hide networking and the complexities of
  distributed computing
• Provides high level services
• Extends storage and transactions across the
  network

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Middleware and Openness
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Middleware Technologies

• CORBA (objects)
• COM (components)
• Java RMI, EJB (components)
• DCE (procedures)
• Proprietary, ie
• Tuxedo, CICS, etc..
• MQ, MSMQ, etc..
• SOAP and Web Services friends

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So What is it Good For?

• Geek answer
• Middleware makes it feasible for mere mortals
  to build distributed software systems that are
• High-performance, scalable
• reliable, high availability
• Dont be fooled.
• Distributed systems are inherently difficult to
  build.

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Solving Business Problems with Middleware

• Legacy system access
• Data integrity
• Scalability
• Availability
• Client access
• Integration

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Legacy System Access
CICS\VSAM
AS400

• Ease legacy system integration by providing
  standard interfaces (wrappers)
• Hides details from clients
• Look like standard objects or components

CICS Gateway
MQ
Server
Server
Middleware Wrappers
Clients
Clients
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Data Integrity

• Ensuring data integrity across distributed
  databases requires transactions
• Transactions ensure ACID properties

Oracle
SQL Server
Server
Server
Clients
Clients
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Scalability

• Provide a framework to scale the system
  performance by service replication
• Requires design good architecture!

Server
Server
Clients
Clients
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Availability

• Replicating data and software to multiple
  machines enhances fault tolerance and improves
  availability
• Duting faults performance degradates, but it
  keeps running

Server
Server
Clients
Clients
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Client Access

• Client access enhanced due to
• Physical distribution
• Any program (or system) can access the middleware
  using a variety of access technologies and
  bridges.

Clients
HTTP
Web Server
Server
IIOP
RMI/IIOP
COM Bridge
Clients
Clients
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Integration

• Allow multiple middleware to interaction using
  standards.
• Standards
• CORBA
• Java
• EJB
• MTS/COM/.NET
• XML and SOAP

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CORBA

• OMG is vendor consortium
• Object Management Group
• Language neutral
• Interfaces defined in CORBA IDL
• Interacts with C, C, Java, Perl, etc...
• CORBA services
• Transactions, naming, events, security

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Java

• Language APIs Class Libraries
• Enterprise Java Beans (EJBs)
• Add declarative services patterns
• API standards
• Java Transaction Service (JTS)
• Java Naming and Directory Interface (JNDI)
• Java Messaging Service (JMS)

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EJBs

• EJBs capture design patterns
• Stateless Session Bean
• Stateful Session Bean
• Entity Bean (bean or container managed)
• Containers/EJB Servers provide
• transaction policies
• security policies
• database connection pooling
• Multi-threading

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MTS/COM/.NET

• Microsofts component architecture
• Pioneered declarative model for
• Transactions, object pooling, security, threading
• Integral part of Windows platform
• Stateless is default model
• .NET uses COM services
• New runtime model only

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XML and SOAP

• XML structured documents
• Standard way to exchange data
• User-defined tags
• Perhaps defined using schemas
• Perhaps displayed using stylesheets
• SOAP XML-based middleware
• RPC calls more in XML
• Wide industry support

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Summary

• Distributed technology
• Critical part in enterprise distributed systems
• Design issues
• Technology issues
• Hard issues
• Testing
• tolerating failures
• Maintaining consistency