Web Architecture

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Web Architecture
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Introduction

• Architecture concept in software development
• From the point of the Unified Process
• Physical architecture
• Computational nodes distribution over the network
• Software component-computational node mapping
• Modern architecture concept
• Architectural design patterns
• Separation of concerns
• There is no way to represent the software
  architecture with current tools (UP-UML)

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Java Web Applications Propagation

• Strong support from software producers
• Sun Microsystems. JEE
• BEA Systems, Weblogic
• IBM, WebSphere
• Netscape (Sun) iPlanet
• Orion Oc4J Oracle 9IAS
• And Strong support from the open source world!
• www.apache.org Development of the apache web
  server, the most used in the world.
• Jakarta.apache.org. Frameworks and support
  classes to support server side web apps
  development over JEE.
• www.jboss.org EJB Container.

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Architectural Models Evolution

• Model 1
• Model 1.5
• Model 2
• Model 2X

Servlets/JSPs
MVC Model
Multichannel
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Architectural model 1 CGI Applications

• The most primitive ones.
• CGI Web apps.
• Presentation, business and persistence
  responsibilities mixed.
• The user state is stored in the client PC and
  each request is a complete transaction
  (Transaction Script)

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Architectural model 1.5JSP Servlets

• Separation of responsabilities
• JSPs for the presentation logic (Navegability,
  rendering, etc.)
• Embedded Beans implement business and persistence
  responsabilities.

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Architectural model 2MVC

• Evolution of the 1.5 model
• It incorporates the MVC pattern.
• Controller Navigability
• Business and Persistence Beans
• Presentation JSPs

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Architectural model 2MVC with Struts

• Struts the reference implementation of the MVC
  that apache provides to implement web apps.
• http//www.apache.org/struts

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Architectural model 2XMultichannel Applications

• Evolution of the model 2 to build multichannel
  applications
• Reference implementation STXX
• http//stxx.sourceforge.net/
• XML XSLTs based solutions

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General Aspects in Web Architecture

• Scalability
• Separation of Concerns
• Portability
• Componentize support services
• User session management, entity caching
• Design patterns use

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ScalabilityImportance?

• Main characteristic of Web applications
• Possible fast increasing of the number of users.
• Its important
• Right sizing of the system
• Adaptability of the system when the demand
  increases.
• Options
• Horizontal scalability
• Vertical scalability
• Cluster of Servers

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Horizontal Scalability

• We clone the system and balance the load

System
System
Internet users
System
System
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Horizontal Scalability. HW Balancer

• Selects the target machine for the HTTP request
  based on pre-configured algorithms (Round Robin,
  LRU, etc.)
• So, the clone is selected randomly.
• Problem No warranty that different request from
  the same user served by the same machine. -gt
  There is no session maintenance in the server -gt
  determines the design!
• Session must be managed by the developer
  explicitly by
• Cookies
• Database
• Its HW-gt Its FAST!

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Horizontal Scalability. SW Balancer

• They examine the request at HTTP level to
  guarantee user session maintenance.
• Different requests from the same user are managed
  by the same server.
• Slower then HW balancers
• Cheap solutions
• Ex., mod mod_jk for apache.

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Horizontal Scalability. HTTP HW Balancer

• HW devices that examines the request at HTTP
  level.
• In the middle of the other ones.
• Warranty of session maintenance.
• Faster than SWB but slower than HWB.

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VerticalScalability

• We implement logic separation of layers in a way
  that we can separate them physically.
• We need a kind of Middleware to allow remote
  invocation

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Scalability with Cluster of Serves

• Common in the commercial Application Servers
  (Weblogic, WebSphere, iPlanet, etc.).
• It can be defined as horizontal or vertical.
• Distributes and scale the system transparently to
  user and administrator.
• Guarantees that regardless of which server
  process the request, it will have access to the
  session of the user. (Session replication)
• Session replication is costly and can decrease
  system performance.

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Separation of concerns

• Base idea for the layer separation
• Different responsibilities should not be managed
  by the same class.
• Current trend in web app.
• n-layers architecture
• Based on the three layers model
• Presentation
• Business
• Persistence
• Independence between layers

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Separation of concerns

• 3 layers architecture

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Separation of concerns

• Brown model, n-layers

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Presentation layer

• All around presentation logic responsibilities
• Navigability
• Input data validation
• Output data formatting
• Internationalization
• Presentation composition.
• Etc.

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Business layer

• Business responsibilities or logic
• Its the result of the functional analysis
• The set of business rules obtained from the real
  world analysis..
• Must be independent of other layers

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Persistence layer

• Anything related with persistence logic, like
  operations
• insert
• delete
• update
• searches
• Etc.
• Not always based on relational databases.

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Portability

• An application should be able to be adapted to
  different physical deploying environments.
• The task of adapting to a new deploying
  environments should be reduced to configuration
  task.
• Example Customer that doesn't want to be forced
  to use EJB components.

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Componentize support services

• support or infrastructure services? Domain
  independent components
• Breaking separation of layers?
• Form the infrastructure layer
• Ex.
• Log service
• Pool JDBC
• Configuration Service
• Authorization service
• Etc.

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User Session Management

• Very Delicate Aspect!
• Entity caching in
• Httpsession object
• Application Context
• Information expiration
• Data refresh
• System performance? We are using server
  resources!

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Design patterns use

• What is a design pattern?
• GOF 94 Design Patterns
• Moreover of being an standard solution, they are
  a communication tool!
• Gets software development faster
• Turns maintenance easier.
• Starting to be integrated in the CASE tools(Rose,
  Together, etc.).

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Thanks!!!

• ?
• Dr. Daniel Fernández Lanvin
• University of Oviedo