CS-422 Enterprise Computing Preview

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CS-422Enterprise ComputingPreview
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Client Server Strategies

• CGI (Common Gateway Interface)
• Active Server Pages
• Personal Home Pages (PHP)
• MS Active Server Pages (ASP)
• Cold Fusion
• Java Servlets and JSP
• Enterprise Java Beans

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CGI

• Program run by web server in response to client
  request
• perl, C, C, VB, Java, python, tcl
• handles submitted HTML forms data and dynamically
  creates a web page in real time and returns it to
  the requesting client
• Old Technology pre- HTTP, rooted in gopher
• reliable
• resource hog

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CGI (more)

• Very useful used in conjunction with Java based
  clients for things like
• Report Generation (WebFocus)
• Data retrieval (files and RDBMS)
• Persistent object storage (files)
• Could almost be replaced by server side Java
• Hard to maintain program state
• must rely on programming tricks
• cookies, hidden variables

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CGI (more)
Static Web page with forms tags ltform
action/CGI-BIN/AAA.PLgt
Browser
Web Server
CGI Program
DB
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CGI (more)

• If another user requests a CGI while the CGI is
  already running the web server spawns a child
  process and runs another instance of the CGI
  there.
• For frequently run CGIs there may be many copies
  in the machine at the same time
• resource hog (web servers that run a lot of
  CGIs will use all of the memory you can afford)

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CGI (more)
Browser
Browser
Browser
Web Server
DB
CGI Program
CGI Program
CGI Program
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Active Server Page Technologies

• HTML pages that appear to be database aware
• HTML with an embedded scripting language and
  either CGI or proprietary server support are used
  to make forms objects appear to be database aware
• Main contenders
• PHP (Open Source)
• Microsoft Active Server Pages (OEM Product)
• Cold Fusion (OEM Product)
• Java Server Pages (Open licensing from Sun)

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PHP (Personal Home Pages)

• Core Technologies
• HTML
• PHP Script
• JavaScript
• Platforms
• Primarily LINUX, Apache
• Windows
• UNIX
• Databases
• Primarily used with MySQL (Open Source)
• Oracle, DB2 (MyODBC Open Source Database Driver))

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PHP (More)

• How it works
• PHP processor usually installs as a CGI that is
  invoked in response to a request for a .php file
  (on Windows NT can run as a service)
• the CGI retrieves the requested file, parses it
  looking for PHP tags
• PHP tags are resolved and the tag is replaces by
  that resolution
• Benefits
• Cheap, Open Source
• Easy to learn
• special HTML-like tags
• very reminiscent of C
• many Open Source, domain specific add ons
  available
• Problems
• Support is typical of Open Source (but quality is
  high)

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PHP (typical) Architecture
HTML
Apache Web Server
JavaScript
MySQL DB
PHP CGI
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Microsoft Active Server Pages

• Core technologies
• MS Internet Information Server
• MS Internet Explorer (IE4.0)
• VBScript
• Java
• ActiveX
• SQL Server Access
• DCOM

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Microsoft Active Server Pages

• Works only on Windows (NT Server and W2000
  Server)

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Microsoft ASP Architecture
HTML
IIS
JavaScript VBScript
VBScript
Java
ActiveX
IE 4.0
Data Base, (Access SQLServer)
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Microsoft ASP

• How it works
• IIS retrieves the requested file, parses it
  looking for Jscript/VBScript and resolves the
  script by replacing it with the resolution
  (values/text)
• Benefits
• A 100 MS solution, important for many corporate
  IS shops
• Easy to learn
• based on VB
• skills are readily available from the large
  number of VB programmers
• easy accessibility to Windows API and DLLs
• Problems
• Security has always been a problem due to MS
  frequent OS and product release cycle

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Cold Fusion

• Core Technologies
• Proprietary, tag based, embedded scripting
  language
• Javascript, Java
• Platforms
• NT, LINUX, Solaris
• Apache, Netscape/iPlanet, IIS
• Databases
• Access, MS SQL Server (NT W/2000 Only)
• Sybase, Oracle, DB2
• MySQL (requires MYODBC driver)

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Cold Fusion Architecture
HTML
Web Server
JavaScript
Java
ODBC JDBC Native
ColdFusion Server
Database
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Cold Fusion

• How it works
• Web server receives request for .cfm file and
  passes the request to the CF server. CF Server
  parses the file returning all non- CF tags to the
  requesting browser and resolving the CF tags into
  their resolved text/values
• Benefits
• Multi-platform
• Easy to learn
• tag based (looks like HTML, gives web community
  comfort that its just some additional tags)
• much support available via the web, wide
  following in the web community
• Problems
• OEM pricing (current price of 5K/server)

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Java Servlets

• Core Technologies
• Java
• HTML, Javascript
• Platforms
• NT, LINUX, Solaris
• Apache/Tomcat, Netscape/iPlanet, JRun
• Databases
• all JDBC enabled (DB2, Oracle, Sybase, Informix)

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Java Servlet Architecture
HTML
Web Server with servlet engine JRE
Servlet Cache
JavaScript
Database
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Java Servlets

• How it works
• Web server receives request for servlet (name is
  mapped to a class file by Java web server) .
  Servlet is loaded into cache and run in the JRE.
  HTML produced by servlet is returned to browser
  
• Benefits
• Cross platform as long as compliant servlet
  engine is availabe
• Easy to learn for Java/C programmers
• much support available via the web
• faster than interpretive technologies (like PHP,
  ASP, CF)
• Problems
• still hard to find skills
• still considered to be bleeding edge by many IS
  shops

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Java Server Pages

• Core Technologies
• Java
• HTML, Javascript
• Platforms
• NT, LINUX, Solaris
• Apache/Tomcat, Netscape/iPlanet, JRun
• Databases
• all JDBC enabled (DB2, Oracle, Sybase, Informix)

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JSP Architecture
HTML
Web Server with JSP engine JRE
Servlet Cache
JavaScript
Database
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What is a JSP

• Combination of HTML, Javascript, and a set of
  Java tags (5)
• Java tags allow java code and calls to Javabeans
  to be embedded in line
• Java tags also allow control of the Java runtime
  environment

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Java Server Pages

• How it works
• Web server receives request for .jsp. JSP engine
  converts the page to source code for a Java
  Servlet, source is compiled by javac and class is
  moved to cache for deployment
• Benefits
• Cross platform as long as compliant engine is
  availabe
• Allows Integrated Product Team development
• faster than interpretive technologies (like PHP,
  ASP, CF)
• Problems
• still hard to find skills
• still considered to be very bleeding edge by
  many IS shops

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Deployment Strategies
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2-Tier Client Server

• Java based Client application or applet
• JDBC
• Database

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2-Tier Client-Server - application
Java Client Application using JDBC APIs
JDBC Enabled Database
TCP/IP
This application architecture is simple but wont
scale to very many users
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2-Tier Client-Server - applet
Unix or Windows
Browser
HTML
Webserver
applet
JDBC Enabled DB
JVM
Webserver and DB must be on same IP address
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2-Tier Problems

• Client has to do everything
• DBs arent meant to handle large numbers of
  transient connections (connections are often more
  expensive than the db transaction being done)
• Good only for infrequently used apps

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3-Tier Client-Server

• Java based Client application or applet
• Server/middleware
• Database

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3-Tier Client Server
Sockets JavaIDL JavaRMI
JDBC Native
Client
Client
Server
DB
Client
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3-Tier Advantages

• Server can manage database connections
  efficiently
• Client can focus on business logic
• Server can preformat data for client
• Running server on high performance hardware can
  improve client perceived performance

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JavaIDL

• In Java we cannot separate a classs definition
  from its implementation as we can in C
• Header files
• Implementation files
• CORBA allows the separation of definition and
  implementation

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JavaIDL

• CORBA uses IDL for defining interfaces, language
  specific IDL compilers are available
• create target language skeletons and stubs to be
  used by developers for building CORBA clients and
  servers
• CORBA objects talk to each other via interfaces

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CORBA Object Communications
IIOP
Object A
Object B
Interface
Interface
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Conceptually ...
Client
Server
Client
Server
ORB
Client
Server
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What happens...

• Server objects register their methods with the
  orb naming service
• Client binds to the orb naming server for a
  server object method
• Naming service returns location of server object
  and disconnects
• Client connects to server at returned location

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Really though...
Registration
ORB
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Client
Server
Services
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Client
Server
3
Client
Server
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This is very simplified

• Very

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Other ORB services...

• Depending on vendor implementation
• automatic failover for servers
• load balancing
• real time, online database

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Orb Info

• The Visigenics VisiBroker Orb is built into
  Netscape Communicator 4.0 to aviod having to
  download 100 Corba class files Netscape browser
  is ready to be a CORBA client
• Borland bought Visigenics
• Borlands and Visigenics vision is a CORBA based
  world
• Why didnt Microsoft buy Visigenics?

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Why MS didnt buyVisigenics

• Wrong vision
• MS Vision is DCOM not CORBA

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CORBA s -s

• Very robust and scalable
• Language independent
• Multi-platform
• very steep learning curve
• specification addresses functionality not a
  standardized API
• every ORB programs differently

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Remote Method Invocation

• Similar to C RPCs
• Instead of creating and instantiating an object
  on your machine create it on another machine and
  communicate with it as if it were a local object
• eliminates much CORBA overhead
• comes with JDK (unlike CORBA)

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RMI

• RMI classes let you generate stubs and skeleton
  layers like JavaIDL
• Remote reference Layer translates stub and
  skeletion calls to native transport calls on the
  host architecture and carries out remote
  reference protocols

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RMI Model
Client
Server
Stubs
Skeletons
Remote
Remote
Reference
Reference
Transport
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RMI

• Currently RMI uses its own on the wire protocol
  that is based on the Java serialization API
• IIOP over RMI is a currently an option for CORBA
  compatibility

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Enterprise Java Beans

• Java, server side component technology
• Application Server Based Technology (IBM
  Websphere, BEA Weblogic, Silverstream, Macromedia
  JRun
• Draws heavily on RMI, CORBA

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EJB Architecture
Application Server
EJB Container
Browser
Database
EJB Server
Transactions
Security
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Transaction Management

• EJBs are transactional by nature
• can be non-transactional but defined for
  distributed transactions
• two-phase commit protocol
• uses Java Transaction Service (JTS)
• Java binding for CORBA Object Transaction
  Service (OTS)
• spans multiple transactions across multiple
  database on multiple platforms
• insures interoperability with other EJB servers

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Persistance

• EJBs provide a simple programming model for
  managing object persistance
• beans can manage their own persistance
• persistance can be managed by the EJB container
• big improvement over active server page
  technologies

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Security

• Java policy based security
• J2EE
• built into JDK since ver 1.1

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EJB Server

• Provides services for the EJB container
• provides distributed transaction management

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EJB Container

• EJB Life cycle management (creation to
  destruction)
• implicit transaction control
• persistance management
• transparent distribution services
• security services
• isolates the developer from platform dependent
  APIs

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Standards based approach

• Based on industry standards (TCP/IP, IIOP, DCOM)
• the model applies to both small scale and large
  scale applications
• transparent access to backend databases (direct
  JDBC/JSQL access is allowed)

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Benefits

• Highly scaleable
• load balancing
• automatic failover
• managed persistance
• high transaction rates
• portability

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Problems

• High capital and software investment
• Steep learning curve
• Considered bleeding edgeand therefore high risk
  by most IS shops.