A Highly Reliable Fault-tolerant Airline Reservation System Zoheb Sait (zs29) Sandeep Varma (sv83)

 Platform:ASP.NET  Programming Languages:C# & VB  Database Server:MS SQL Server 2000  Group Communication System:Spread Software

Architecture Prototype used:  Two Web Servers  Two Database Servers  Single Load Balancer  -- Easily Scaleable

Failover  Database level:  Reads from any database server  Synchronous writes to all database servers through Spread  Transparent Failover  Auto-Reconfiguration and synchronization into group on recovery  Application Server level:  Load Balancer maintains list of available web servers  LB does transparent redirect of offline web server load to available web servers

Processes  The database replication is provided by a process named ‘SpreadListener’ a daemon which runs as a windows service  ‘HeartBeatMonitor’ provides transparent fail-over to available database servers  ‘Load Balancer’ distributes clients requests in round-robin manner, and provides transparent web server fail-over

Test: 500 users connecting in intervals of 2 sec in 5 users batch at a time Case 1: Replication Disabled v/s Enabled  Average Response time was 74ms with replication enabled  Average response time was 51ms with replication disabled Performance Tests

Case 2: LB and Replication v/s No LB and Repl  Average Response time was 51ms with load balancing and replication disabled  Average Response time dropped to 19ms with load balancing and replication. Performance Tests

 With replication disabled:  ~200 errors  With replication enabled:  ~400 errors  Maximum number of concurrent transactions without failure:  ~ 60 transactions/per sec without a load balancer  ~ 90 concurrent transactions per/sec with a load balancer Application Stress Test