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National Online Examination System: An Architectural Perspective:

National Online Examination System: An Architectural Perspective Pradeep Kumar , Pankaj Nirwan , P Govind Raj

Background:

Background NASSCOM Recommendation to the Government of India DIT realizing the initiative through C-DAC Objective: Design and Develop a robust, fault tolerant, secure, and scalable and an adaptive system through which examinations can be delivered on an “on demand” basis in selected examination centers spread across the country. Implementation Phases Phase 1: Software for conducting exams at National Levels to be rolled out. Phase 2: Collaborative environment for collecting Questions into the question bank.

Why not use Standard LMS ?:

Why not use Standard LMS ? Designed to deliver content and manage the teaching learning process. Not designed to handle large system loads Computer Adaptive Testing is not incorporated.

Functional Requirements :

Functional Requirements

Non Functional Requirements:

Non Functional Requirements No Vendor Lock in. Scale Out Vs Scale Up. Ease of Extendibility High System Throughput High Availability Security/Privacy Key Escrow Mechanisms

High Level Architecture:

High Level Architecture Blaze DS Remoting Tier Flash Player Browser/AIR UI on Flex Presentation Tier Business Tier ORM Hibernate DB Spring Core Context AOP Transaction JDBC Security ORM ORM Tier Data Tier Persistence Logging Tomcat on Tuned JVM

High Level Architecture:

High Level Architecture Blaze DS Remoting Tier Flash Player Browser/AIR UI on Flex Presentation Tier Business Tier ORM Hibernate DB Spring Core Context AOP Transaction JDBC Security ORM ORM Tier Data Tier Persistence Logging Tomcat on Tuned JVM AS3 VO Java

High Level Architecture:

High Level Architecture Blaze DS Remoting Tier Flash Player Browser/AIR UI on Flex Presentation Tier Business Tier ORM Hibernate DB Spring Core Context AOP Transaction JDBC Security ORM ORM Tier Data Tier Persistence Logging Tomcat on Tuned JVM AS3 VO

High Level Architecture:

High Level Architecture Blaze DS Remoting Tier Flash Player Browser/AIR UI on Flex Presentation Tier Business Tier ORM Hibernate DB Spring Core Context AOP Transaction JDBC Security ORM ORM Tier Data Tier Persistence Logging Tomcat on Tuned JVM AS3 VO Java VO

High Level Architecture:

High Level Architecture Blaze DS Remoting Tier Flash Player Browser/AIR UI on Flex Presentation Tier Business Tier ORM Hibernate DB Spring Core Context AOP Transaction JDBC Security ORM ORM Tier Data Tier Persistence Logging Tomcat on Tuned JVM AMF

Business Tier: Spring:

Business Tier: Spring Aspect Orientation Design Declarative Transaction Management Security Lightweight Use POJO’s to manage transactions , persistence , communication , job scheduling , batch processing etc. Productive Easy to learn. Jolt’s productivity Award 2006

Security Subsystem:

Security Subsystem

Security Subsystem Architecture:

Security Subsystem Architecture Request Login Credentials Login Credentials are put in Flex User Interface. BlazeDS Channel Authentication The BlazeDS Channel Authentication would be done using Spring Security by contacting a User Repository. FilterInvocationInterceptor URIInterceptor MethodSecurityInterceptor TransactionProxy Spring Security Interceptors

Role Based Access Control:

Role Based Access Control Access Decision through AcessDecisionManagers Affirmative Based Access decision Manager Role Voter Grant access of the resource to the user that has the same role as required by the resource

Deployment Architecture:

Deployment Architecture

Horizontal Clustered Environment:

Horizontal Clustered Environment L B L B Active Passive Clustered Load Balancer based on Apache mod_proxy , mod_proxy _balancer

Horizontal Clustered Environment:

Horizontal Clustered Environment L B L B Tomcat Application Server Load Balancing: ByByte / ByRequest Tomcat 1 Tomcat 1

Horizontal Clustered Environment:

Horizontal Clustered Environment L B L B Design Deviates from conventional HA Solution Tomcat 1 Tomcat 1 MYSQL

Horizontal Clustered Environment in NOES:

Horizontal Clustered Environment in NOES L B L B Tomcat 1 Tomcat 1 MYSQL T E R R A C O T A MYSQL

Transparent Clustering:

Transparent Clustering

Transparent Clustering:

Transparent Clustering HA is available as a service of JVM

Key Design Principles:

Key Design Principles

Typical Exam Session Performance:

Typical Exam Session Performance

Typical Exam Session Performance:

Typical Exam Session Performance No DB I/O during Exam

Typical Exam Session Performance:

Typical Exam Session Performance Hibernate 2 nd Level Cache

Typical Exam Session Performance:

Typical Exam Session Performance Async . Commit

Issues faced during implementation:

Issues faced during implementation

Integrating Flex and Spring:

Integrating Flex and Spring Integration Flex and Spring Not intuitive BlazeDS Extensions were designed Later , later 2009 community support Transaction MySQL Storage Engines Transaction Management for Non DB operations Use of Self Reference instead of this pointer

Conclusion and Future Work:

Conclusion and Future Work Exams Conducted C-DAC PG Examinations C-DAC Recruitment Exams Across the country in 10 C-DAC Centers for 10 days 300 successful runs of Exam Conduction DOEACC ‘CCC’ Examination at 4 Regional DOEACC Centers. Initial Stress Testing 5,000 users using 2 Tomcat Servers Trying to scale further Efforts in integration with Eucalyptus and federate across different C-DAC/DOEACC Data centres in the country. Using Query Optimization with Hibernate on the Fly.

Thank You:

Thank You

Aspect Orientated Design:

Aspect Orientated Design Module 1 Module 1 Module n

Aspect Orientated Design:

Aspect Orientated Design Module 1 Module 2 Module n Security Logging

Aspect Orientated Design:

Aspect Orientated Design Module 1 (core Concerns) Module 2 (Core concerns) Module n (Core Concerns) Security (Cross Cutting Concerns) Logging(Cross Cutting Concerns)

OOD to Model Cross Cutting Concerns:

OOD to Model Cross Cutting Concerns Module 1: Functional Req. Module 2: Functional Req. Cross Cutting Concern Cross Cutting Concern

OOD to Model Cross Cutting Concerns:

OOD to Model Cross Cutting Concerns Module 1: Functional Req. Module 2: Functional Req. Cross Cutting Concern Cross Cutting Concern Code Scattering Code Tangling

AOD to Model Cross Cutting Concerns:

AOD to Model Cross Cutting Concerns Module 1: Functional Req. Module 2: Functional Req. Cross Cutting Concern Aspect Weaved Weaved

Aspect Orientation at Business Tier:

Aspect Orientation at Business Tier Logging Transaction Management Declarative Transactions Annotations (@Transactional PROPOGATION_LEVEL) Access Control Mechanism Annotations based RBAC at method invocation level.

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