Distributed News Aggregator

Fault tolerence distributed system written in Java, to comply with ATOM XML and HTTP

Features Implemented

• HTTP compliant messages passed between nodes (200, 201, 204, 400, 500)
• Semi-featured XML parsing
• Aggregation of Content Server entries into feed
• Thread safe reader-writer locks around resources in memory and disk
• Priority handling of single byte messages as probes
• Adaptive timeouts on clients waiting for responses
• Displaying feed received from server on GetClients
• Fault tolerance on server, will initialise back to the previous checkpoint
• Fault tolerance on content servers, restore cookie and last received hash
• Heartbeat from content serves using HTTP Head requests
• Removal of expired feeds from memory and file after 15 seconds
• Lamport clocks on all classes that are synchronising and updating on message passing
• Requests are queue and worker threads created by Lamport clock priority
• Support for event logging across components of the system
• Support for automated testing scenarios via stoppable threads

To Do

• Improve XML parsing to reflect full spec (Aggregate aggregates, not entries)
• GetClient Head requests to monitor changes to the feed
• Better handling of socket exceptions (Currently Ignored)

Changelog

• Support for event logging across components of the system
• Support for automated testing scenarios via stoppable threads
• Added several scenarios that can be run using the instructions below
• Refactored code and converted utility classes to static
• Added a file system lock for thread safe file acess
• Final Spellcheck

To Run Manually

• Compile all .java files in the assignment2 directory
• Launch separate VM instances for each of the nodes
• java AggregationServer
• Starts the server listening for requests
• java PutClient
• Starts a PutClient that loads the content.txt as its content
• java GetClient
• Starts a client that makes a get request to the server and prints out the received feed

Automated Testing

• By default all tests will run, comment tests out from the main of TestUtil as required
• Compile all .java files in the assignment2 directory
• java TestUtil
• Runs through the following scenarios:
  • Get request
  • Put without content
  • Put with content and heartbeat
  • Put with sequential Get
  • Multiple Puts then Get
  • Put with Multiple Gets
  • Multiple Puts with Multiple Gets
  • Interleaved Put and Get
  • Feed Expiries due to non-contact
  • Server Restart during uptime
  • Put Client Restart during uptime
  • Put Client failure without restart
• Logs for each of the actors in the distributed system are recorded in Testing Logs
• Each test scenario's logs are stored in a separate folder titled with the test